Antimicrobial copper
By Jason Ren
Contents Page:Abstract……………………………………………………………………………………………………3Aim…………………………………………………………………………………………………………..3Background Information……………………………………………………………………………3Equipment………………………………………………………………………………………………17Hypothesis………………………………………………………………………………………………17Variables…………………………………………………………………………………………………18Controls…………………………………………………………………………………………………..18Procedure………………………………………………………………………………………………..18Risk assessment……………………………………………………………………………………….26Results……………………………………………………………………………………………………..27Calculations..………………………………………………………………………….…………………28Analysis……………………………………………………………………………………………...……30Discussion………………………………………………………………………………………………..34Conclusion………………………………………………………………………………………………..39Bibliography……………………………………………………………………………………………..40Appendix…………………………………………………………………………………………………..43
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Date: 9 June- 25 June
Abstract:
Antibiotic resistant bacteria are a prominent issue in modern day society and are
becoming more prevalent in many clinical environments such as hospitals.
Infections caused by antibiotic and non-antibiotic resistant bacteria are often
spread by contact surfaces such as handrails, door handles, taps, and toilet seats.
Copper surfaces have been suggested to have antimicrobial properties, killing up
to 90% of bacteria and has been proposed as an alternative to stainless steel and
plastic surfaces. Cells exposed to copper surfaces have been shown to suffer
extensive membrane damage and showed loss of cell integrity.
Aim:
To determine if copper surfaces can be used as an antimicrobial agent to limit
bacterial growth and if it has practical applications in clinical healthcare
environments such as hospitals
Background Information:
Bacterial cell structure
First seen under a microscope in 1676 by Anton Van Leeuwenhoek, bacterial
cells are much smaller then plant or animal cells. As microscope technology has
improved, scientists have come to understand bacterial cell structure in more
depth. A bacterial cell is made up of different parts such as the capsule, cell wall,
plasma membrane and the nucleoid1. The cell membrane is the semipermeable
membrane that surrounds the cytoplasm of a cell and has numerous roles. These
roles encompass a variety of functions such as energy generation and transport
of solutes as well as housing many enzyme systems2. The plasma membrane is
predominantly composed of phospholipids and proteins. Within the cell
membrane are the cytoplasm, ribosomes, mesosomes, plasmid and the nucleoid3.
1 Structure and Function of Bacterial Cells. 2015. Structure and Function of Bacterial Cells. [ONLINE] Available
at:http://textbookofbacteriology.net/structure.html. [Accessed 25 June 2015]
2 BBC - GCSE Bitesize: Plant and animal cells. 2015. BBC - GCSE Bitesize: Plant and animal cells. [ONLINE] Available at:http://www.bbc.co.uk/schools/gcsebitesize/science/add_edexcel/cells/cells2.shtml. [Accessed 25 June 2015]3 Bacterial DNA – the role of plasmids | Biotech Learning Hub. 2015.Bacterial DNA – the role of plasmids | Biotech Learning
Hub. [ONLINE] Available at:http://biotechlearn.org.nz/themes/bacteria_in_biotech/bacterial_dna_the_role_of_plasmids.
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The cytoplasm is where metabolic processes necessary for life occur. Ribosomes
are sites of protein synthesis, i.e. they are involved in the manufacture of
proteins. The nucleoid is the area that contains the cell’s DNA. Mesosomes play a
role in cellular respiration, which is a process that breaks down food to release
energy. The plasmid contains extrachromosomal genetic material. These genes
are usually not necessary for the bacterium’s day-to-day survival. Instead, they
help the bacterium overcome, for example, situations where it is exposed to
antibiotics. In these instances many plasmids, contain genes that when expressed
make the bacterium resistant to antibiotics. Other plasmids can also contain
genes that help the bacterium kill other bacteria. Without these important
structures such as ribosomes and mesosomes, the bacterial cell cannot function
properly and may quickly die.
Antibiotics
Antibiotics are medicines used to treat diseases or infections cause by bacteria.
Antibiotics differ in how they work and the types of bacteria they work against.
The main classes of antibiotics include: penicillins, cephalosporins4, macrolides,
aminoglycosides and fluoroquinolones5. Cephalosporins and penicillins kill
bacteria by destroying bacterial cell walls. Macrolides and aminoglycosides work
by binding to a specific subunit of ribosomes in susceptible bacteria, inhibiting
the formation of bacterial proteins6. This action in most organisms inhibits cell
growth, however in high concentrations it can cause cell death. The protein that
the antibiotic aims to inactivate is sometimes referred to as the target protein7.
Fluoroquinolonies can cause sever side effects in rare cases, and are therefore
[Accessed 25 June 2015]
4 Antibiotics Causes, Symptoms, Treatment - Types of Antibiotics - eMedicineHealth. 2015. Antibiotics Causes, Symptoms,
Treatment - Types of Antibiotics - eMedicineHealth. [ONLINE] Available
at:http://www.emedicinehealth.com/antibiotics/page2_em.htm. [Accessed 25 June 2015]
5 http://pharmaxchange.info/press/2011/05/mechanism-of-action-of-quinolones-and-fluoroquinolones/ (Akul, M.
(2011). “Mechanism of Action of Quinolones and Fluorquinolones”. 10th May)
6 Overview - Biology Online. 2015. Overview - Biology Online. [ONLINE] Available at:
http://www.biology-online.org/articles/aminoglycoside.html. [Accessed 13 August 2015].
7 What are antibiotics and how do they work? | NPS MedicineWise. 2015.What are antibiotics and how do they work? | NPS MedicineWise. [ONLINE] Available at: http://www.nps.org.au/medicines/infections-and-infestations/antibiotics/for-individuals/what-are-antibiotics-and-how-do-they-work. [Accessed 25 June 2015]
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not used for regular treatment of bacterial infections. They are used for more
resistant strains of bacteria and work by blocking DNA replication pathways of
bacteria thereby inhibiting bacterial replication.
Antibiotic resistant bacteria
Antibiotic medications are used to kill harmful bacteria, which can cause disease
and illness. They have made a major contribution to human health, however,
some bacteria have become resistant to commonly used antibiotics, an example
being Methicilim-resistant Syaphylococcus Aureus, better known as MRSA8.
Antibiotic resistance is a current public health problem and can cause serious
widespread disease. Some bacteria are naturally resistant to some antibiotics.
For example benzyl penicillin has very little effect on most organisms found in
the human digestive system. The first step in the emergence of resistance in
bacteria is a genetic change9. There are various ways this can happen; two
methods include spontaneous mutation in the bacterium’s DNA and transfer of
antibiotic-resistance genes. Many antibiotics, e.g. Penicillin, work by inactivating
an essential bacterial protein. Not only can a genetic change can remove that
protein, mutations in the target protein can prevent the antibiotic from binding,
or if its does bind; prevent it from inactivating the target protein10. To prevent
the antibiotic from binding with the target, some bacteria change the structure of
the target so that the antibiotic can no longer recognize it or bind to it. Genetic
change can also lead to increased production of the target enzyme of an
antibiotic, so that there are too many for the antibiotic to inactivate. Alternatively
the bacterium may produce an enzyme that inactivates antibiotics. An example is
an enzyme called beta-lactamases that “inactivate” penicillin. In addition, to stop
antibiotics form entering the cell, the bacterium may alter the permeability of its
cell membrane. The second method for a bacterium to gain resistance is by the
transfer of an antibiotic-resistance gene from one bacterium to another
8 Antibiotic resistant bacteria | Better Health Channel. 2015. Antibiotic resistant bacteria | Better Health Channel. [ONLINE] Available at:http://www.betterhealth.vic.gov.au/bhcv2/bhcarticles.nsf/pages/Antibiotic_resistant_bacteria. [Accessed 25 June 2015]9 How bacteria become resistant. 2015. How bacteria become resistant. [ONLINE] Available at:
http://www.abc.net.au/science/slab/antibiotics/resistance.htm. [Accessed 13 August 2015].
10 How do bacteria become resistant to antibiotics? - HowStuffWorks. 2015. How do bacteria become resistant to antibiotics? - HowStuffWorks. [ONLINE] Available at: http://science.howstuffworks.com/environmental/life/cellular-microscopic/question561.htm. [Accessed 13 August 2015].
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bacterium. Antibiotic resistance not only spreads due to the transfer of
antibiotic-resistance genes, but through the movement of bacteria form one host
to another, either indirectly or directly. In humans, when a course of antibiotics
is taken there is always the chance that there will be some bacteria with
resistance, as well as the fact that often the full course of antibiotics is not taken.
Those not killed are now free to multiply without any competition form weaker
strains. Friendly bacteria can also be wiped out by antibiotics, which would
otherwise compete with the resistant strain for resources.
In modern day society, bacteria are gradually increasing its resistance to
antibiotics. The world currently has a demand for a new antibiotic, but finding
one is proving to be a great challenge. However copper may be the key to killing
antibiotic resistant bacteria such as MRSA as well as improving general health by
limiting bacteria growth.
What is copper?
Copper (Cu) is one of the best electrical conductors of metals. Light red in colour
and easily oxidized to a green hue, copper can be formed and drawn to serve
many purposes from water pipes and circuit boards to jewellery and
architecture, and in the case of this project to possibly replace common contact
surfaces made out of materials such as plastic, to limit bacteria growth, in
hospitals.
Possible property of copper that kills bacteria
Properties of copper thought to kill bacteria include its high conductivity as well
as the release of copper ions when contact between bacteria and the metallic
surface occurs.
What differentiates copper from antibiotics?
In the context of killing bacteria, copper does not kill bacteria via “conventional”
methods used by antibiotics. In stead it uses other methods such as in causing
holes to appear in the cell membrane. The antibiotic penicillin causes a similar
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reaction in bacteria to kill bacteria. However it does so by targeting proteins and
enzymes in the membrane. Resistance to this action has already emerged and
can be spread easily. On the other hand a proposed method of how copper
creates holes is that copper essentially “Short circuits” the cell membrane11. This
is an example of how copper attacks bacteria from “another direction”, i.e. it kills
bacteria in in a different way, when compared to antibiotics. Another, perhaps
more important factor that differentiates copper form antibiotics, is that copper
can kill drug resistant “superbugs”. In other words, copper can kill some
antibiotic resistance bacteria. Studies conducted have shown that copper
surfaces can kill E.Coli, Clostridium difficile, Influenza A, Adenovirus, and
perhaps the most infamous of them all Methicillin-resistant Staphylococcus
aureus, better known as MRSA. In 2004 the University of Southampton research
team conducted an experiment that demonstrated copper inhibiting the growth
and replication of MRSA. This study found that “Faster antimicrobial efficacies
were associated with higher copper alloy content”, and that “stainless steel did
not exhibit any bacterial benefits”. Furthermore, in 2008, the United States
Environment Protection Agency (EPA)12, after evaluating a wide body of
research, granted a registration approval that certified “copper alloys kill more
that 99.9% of MRSA within two hours”13.
Proposed methods of how copper kills bacteria
Research has been conducted in the area of how copper kills bacteria, however
results are not certain and are subject to disagreement. The most conclusive and
evidence backed property of copper that kills bacteria is through contact killing.
Although the mechanism of contact killing is still not fully understood, recent
studies suggest that copper surfaces kill bacteria by a three-pronged attack:
damage of the bacterial membrane, extensive intracellular damage, and DNA
degradation. The sequence of these events is still under debate and may be
11 The Science behind Antimicrobial Copper. . 2015. The Science behind Antimicrobial Copper. . [ONLINE] Available at:http://antimicrobialcopper.com/us/scientific-proof/how-it-works.aspx. [Accessed 25 June 2015]12 Killing of Bacteria by Copper Surfaces Involves Dissolved Copper . 2015.Killing of Bacteria by Copper Surfaces Involves Dissolved Copper . [ONLINE] Available at:http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2893463/. [Accessed 25 June 2015]13 Antimicrobial properties of copper - Wikipedia, the free encyclopedia. 2015. Antimicrobial properties of copper - Wikipedia, the free encyclopedia. [ONLINE] Available at: https://en.wikipedia.org/wiki/Antimicrobial_properties_of_copper. [Accessed 13 August 2015].
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different depending on the microorganism. For many organisms, copper as a
trace element is an essential nutrient. Furthermore, in respiration, copper serves
as a cofactor and is thus needed for aerobic metabolism. However, when copper
is in excess and in high concentrations, it is highly toxic. Every cell’s membrane
including both multicellular and single celled organisms like bacteria contains a
stable electrical micro-current, often called “trans membrane potential” and is
essentially the voltage difference between the inside and outside of a cell. It is
suspected that when bacterium comes into contact with a copper surface, a
short-circuiting of the current in the cell membrane can occur. This may be due
to the high conductivity of copper. This short-circuiting weakens the membrane
and creates holes. Another method that holes may be opened in the membrane is
through the interaction of copper ions with lipids causing their peroxidation14.
The opening of holes in the cell membrane can compromise the integrity of the
cell, which can cause the leakage of essential solutes resulting in a desiccating
effect. Once the cell membrane has been breached, there is essentially an
unopposed stream of copper ions entering the cell. It is at this stage that most of
the damage is done to the cell. Copper readily catalyses reactions that result in
the production of hydroxyl radicals through Haber-Weiss and Fenton reactions.
Hydroxyl radicals can damage virtually all types of macromolecules; some
examples include nucleic acids, amino acids and lipids. The formation of radicals
can also inactivate viruses. Highly reactive oxygen intermediates causes lipid
peroxidation and oxidation of proteins. In other words, in this process, lipids and
proteins are degraded by oxidation. Copper ions inactivate proteins by damaging
Fe-S clusters as well as by replacing the respective metals in metalloproteins
with copper. Copper ions may also disrupt enzyme structures and functions by
binding to sulphur. To put it simply, copper ions entering cells puts vital
processes inside the cell in danger. Copper can obstruct cell metabolism as well
as stopping enzymes inside the cell from performing vital functions. This occurs
when the copper ions make molecular bonds with these enzymes. For
Escherichia coli (E-Coli) in particular, copper damage to the respiratory chain in
14 Antimicrobial metallic copper surfaces kill Staphylococcus haemolyticus via membrane damage. 2015. Antimicrobial
metallic copper surfaces kill Staphylococcus haemolyticus via membrane damage. [ONLINE] Available
at: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3426407/. [Accessed 25 June 2015]
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E-Coli cells has been linked with impaired cellular metabolism. Recently in 2014,
live/dead staining performed in various studies indicated that cell membrane
damage occurred in cells on copper surfaces but not steel surfaces. These
findings suggest that metallic copper does not kill via DNA damage. In contrast,
membranes are most likely the Achilles heel of cells exposed to copper. Although
copper may not kill via DNA damage it still may degrade DNA when “attacking”
cells.
Further studies of antimicrobial properties of copper found that the surface
structure of copper as well as the environment that it was in affected the rate at
which bacteria was killed15. The importance of the release of copper ions in the
killing of bacteria implies that the surface structure of a copper surface is a factor
in the rate at which bacteria is killed. A study performed by the National Centre
for Biotechnology Information (NCBI) found that contact killing of bacteria in
copper is essentially supressed if bacterial contact with metal is prevented16.
This is an important issue as over time, copper corrodes to develop a green
verdigris (or patina). This layer of verdigris may inhibit the ability of copper to
kill bacteria. On the other hand, the more contact a copper surface has with
bacteria, the higher the rate at which bacteria is killed. A possible explanation for
this is that the more contact the copper surface has with bacteria the faster it
corrodes. Faster corrosion rates have been correlated with faster inactivation of
microorganisms. The rational behind this is that a higher corrosion rate means a
increased availability of cupric ions (copper ions with a +2 charge), which is
believed to be one of the factors responsible for copper’s antimicrobial action.
Bacteria-metal contact can also be prevented by a build up of dead bacteria. This
dead bacteria can act as a barrier between the “healthy and alive” bacteria and
the copper surface. As discussed above, if bacterial-metal contact is prevented
then the killing of bacteria is supressed. However, the barrier of dead bacteria 15 Surface structure influences contact killing of bacteria by copper. 2015.Surface structure influences contact killing of bacteria by copper. [ONLINE] Available at: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4082706/. [Accessed 25 June 2015]16 Contact Killing of Bacteria on Copper Is Suppressed if Bacterial-Metal Contact Is Prevented and Is Induced on Iron by
Copper Ions. 2015. Contact Killing of Bacteria on Copper Is Suppressed if Bacterial-Metal Contact Is Prevented and Is
Induced on Iron by Copper Ions. [ONLINE] Available at: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3623184/.
[Accessed 13 August 2015].
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will eventually be broken down and new bacteria will come into contact with the
copper surface. Dead bacteria can also be removed by cleaning the copper
surface. Furthermore, dry copper surfaces killed bacteria faster and in larger
numbers then moist copper surfaces. An explanation is that the intake of copper
ions is faster form dry copper than from moist copper17. In addition, moist
surfaces promote bacterial growth, whereas dry surfaces do not.
Bacterial growth
Bacterial growth is generally dependent on the existence of water, however
there are some parameters for optimum bacterial growth.
1. Supple of suitable and retrievable nutrients- the nutrients present should
be in a form that allows the bacterial cell to passively or actively intake
them18
2. Existence of water- as mentioned above, bacterial growth is strongly
dependent on water. Dry surfaces doe not promote bacterial growth
3. Presence of a source of carbon or other forms of energy- all life forms that
exist take up some form of energy to survive. For example,
microorganisms that perform photosynthesis and receive primary energy
from sunlight, require the gas carbon dioxide as a carbon source
4. Existence of appropriate temperature- different microorganisms have
different requirements regarding temperature for optimum growth. E-
Coli falls into the category of mesophiles and has an optimum growth
temperature of 370C. Mesophiles are bacteria that can grow and divide
between 100C-450C19
5. Appropriate pH of the environment- most microorganisms including E-
Coli, grow best when the pH is around 7(neutral pH)
Methods of sterilisation and disinfecting
17 Bacterial Killing by Dry Metallic Copper Surfaces . 2015. Bacterial Killing by Dry Metallic Copper Surfaces . [ONLINE] Available at:http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3028699/. [Accessed 25 June 2015].18 New Page 2. 2015. New Page 2. [ONLINE] Available at: http://classroom.sdmesa.edu/eschmid/Lecture4-Microbio.htm. [Accessed 13 August 2015].19 Growth Requirements of E. coli. and Auxotrophs - Video & Lesson Transcript | Study.com. 2015. Growth Requirements of E. coli. and Auxotrophs - Video & Lesson Transcript | Study.com. [ONLINE] Available at: http://study.com/academy/lesson/growth-requirements-of-e-coli-and-auxotrophs.html. [Accessed 25 June 2015]
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Disinfecting is a process of reducing or eliminating harmful microorganisms.
Sterilisation refers a chemical or physical process that completely removes or
destroys all viable microorganisms20. The destroying of all microorganisms is the
main difference between disinfecting and sterilizing. Disinfecting can be
performed by application of bleach, detergents and alcohols. Alcohols with a
concentration of 70% can be used to quickly and efficiently disinfect surfaces21.
In contrast to external surfaces, internal surfaces such as the inside of a pipe may
be harder to reach and may take longer to clean. Due to the rapid evaporation of
alcohol, extended contact times are more difficult to achieve. Consequently,
submersion of the item in alcohol is suggested when trying to clean internal
surfaces with alcohol. This property of alcohol makes it useful for cleaning
objects such as copper and PVC tubing. Heat is both a method that can be use to
disinfect or sterilize. However, using heat to disinfect copper and plastic surfaces
would not be a practical method in this project. In contrast, the use of heat is
useful to sterilize inoculation loops. In a process called flaming, inoculation loops
are sterilised before and after the retrieval of bacteria. It is also recommend that
when transferring bacteria from a slope to an external location such as a broth,
the mouth of the container, if it is made of glass, should be flamed prior to and
after the bacteria is transferred22.
Aseptic technique in microbiology
Some practices of microbiology relevant to this experiment include setting out
the workspace, inoculating agar plates and flaming inoculation loops and necks
of bottles.
Setting out the workspaces
20 2.1 Cleaning, Disinfection & Sterilisation . 2015. 2.1 Cleaning, Disinfection & Sterilisation . [ONLINE] Available
at:http://www.health.qld.gov.au/EndoscopeReprocessing/module_2/2_1.asp. [Accessed 25 June 2015]
21 Disinfectants and Sterilization Methods | Environmental Health & SafetyEnvironmental Health & Safety | CU-Boulder .
2015. Disinfectants and Sterilization Methods | Environmental Health & SafetyEnvironmental Health & Safety | CU-Boulder .
[ONLINE] Available at:http://ehs.colorado.edu/resources/disinfectants-and-sterilization-methods/. [Accessed 25 June
2015]
22 Aseptic techniques | Nuffield Foundation. 2015. Aseptic techniques | Nuffield Foundation. [ONLINE] Available at:http://www.nuffieldfoundation.org/practical-biology/aseptic-techniques. [Accessed 25 June 2015]
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- To reduce the chance that air might be disturbed by a draught, all
windows and doors should be closed
- The experiment should only begin once all apparatus and materials are
within immediate reach
Inoculating agar plates
- Inoculation and transfer of microbes should be conducted under a
laminar flow
- A laminar flow is where air currents are drawn upwards, this can be
achieved by working close to a Bunsen burner flame
- Transfer of microbes between surfaces should be conducted as quickly as
possible with the agar plate being open to the air for least amount of time
possible
Flaming inoculation loops and necks of bottles
- Inoculation loops should be flamed prior to and after use
- The loop should be flamed by passing the wire through the hottest region
of the flame, and held in the flame until the wire is red-hot. All parts of the
wire should flamed. The image below is a visual representation of the
flaming process
- After the loop is flamed allow it to cool for a few seconds in the air before
using it immediately
- Note: The flaming procedure should heat the wire of the loop gradually, as
after use, it will most likely contain some sort of residue which may
splutter on rapid heating. This may result in small particles of the residue
becoming airborne.
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- Flaming of neck of bottles aims the ensure that no microorganisms
contaminate the medium or culture by entering the mouth of the
container
- Passing the mouth of the bottle through a flame produces a convection
current away from the opening, which helps prevent contamination
Calculating CFU/ml
Colony Forming Units per ml (CFU/ml) can be used as a method to measure
viable bacterial or fungal cells23. It is important to note that CFU only measures
viable cells. Viable cells can be defined as the number of cells in a given area of
volume that are thriving24. CFU/ml can be calculated using the formula:
CFU/ml= (number of colonies)/(Volume of culture plated x Dilution factor)
The number of colonies can be found by counting the number of colonies in the
culture plate, i.e. an agar plate. The dilution factor is essentially a measure of how
diluted a solution is and is usually measured by “factors of ten”25, for example, a
solution would be diluted “by a factor of ten or a hundred”, rather than a factor of
50.
The dilution factor can be calculated by using the formula
C1V1=C2V2
Where:
V1= Volume of stock solution needed to make new solution
C1= Concentration of stock solution
V2= Final volume of new solution
23 efinition of viable cell count by Medical dictionary. [ONLINE] Available at: http://medical-
dictionary.thefreedictionary.com/viable+cell+count. [Accessed 25 June 2015]
24 Bio-Resource: CFU: Colony Forming Unit & Calculation. 2015. Bio-Resource: CFU: Colony Forming Unit & Calculation. [ONLINE] Available at:http://technologyinscience.blogspot.com.au/2011/11/cfu-colony-forming-unit-calculation.html#.VYFXGEKaK2R. [Accessed 25 June 2015]25 Dilutions: Explanations and Examples of Common Methods | Quansys Biosciences. 2015. Dilutions: Explanations and Examples of Common Methods | Quansys Biosciences. [ONLINE] Available at:http://www.quansysbio.com/dilutions. [Accessed 25 June 2015]
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C2= Final concentration of new solution, i.e. how much it is diluted by. For
example if C2=0.1 then new solution would be diluted by a factor of 10.
Actual studies conducted
Various studies have been conducted by reliable sources such as governments
and reputable academic journals in the area of antimicrobial copper. Of the
studies researched, all came to a conclusion, which contained essentially the
same theory, that copper inhibits the growth of bacteria. A study published by
The Journal of Hospital Infection, demonstrated that installing copper surfaces in
healthcare environments reduces the risk of acquiring HCAI26. Another extensive
study published by The University of Chicago Press on behalf of The Society for
Healthcare Epidemiology of America found that copper alloys containing more
than 60% copper reduced amount of bacteria on solid surfaces in an outpatient
environment by 99.9% within 2 hours27. This study also found that copper
surfaces were able to diminish bacteria levels to below those considered a risk
for patients for acquiring an infection. The study was conducted by replacing
common touch surfaces on phlebotomy chairs in an outpatient infectious disease
clinic such as armrests and plastic trays with a copper alloy metal containing
90% copper and 10% nickel. A total of 437 patients using the chairs over a 15-
week study period were recorded. The results showed that copper surfaces
reduced the bacterial population present on the arm surfaces and trays. A
reduction of 90% on copper arm rests for total aerobic bacteria and an 88%
median reduction on copper trays was observed. This study did take into
account outliers with 17 data points being removed from the analysis. Some data
was removed due to no patients using a particular chair on that day and other
data was removed due to sample damage.
26 DEFINE_ME_WA. 2015. DEFINE_ME_WA. [ONLINE] Available at:http://www.journalofhospitalinfection.com/article/S0195-6701(12)00165-X/abstract. [Accessed 25 June 2015]27 2015. . [ONLINE] Available at: http://www.asminternational.org/eNews/copper_hospchair.pdf. [Accessed 14 August 2015].
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Amount of bacteria (CFU/100cm2) on two phlebotomy chairs sampled in the experiment
Another study which has its initial results presented at the World Health
Organization’s first International Conference on Prevention and Infection
Control (ICPIC) in Geneva, Switzerland on 1 July 2001, showed that from a
comprehensive, multi-site clinical trial in the United States, copper surfaces in
intensive care unit rooms demonstrated a 40.4% reduction in the risk of
acquiring a hospital infection28. Researches in the three hospitals involved in the
clinical trial; Memorial Sloan Kettering Cancer Centre in New York, the Medical
University of South Carolina, and the Ralph H. Johnson VA Medical Centre,
replaced commonly touched surfaces such as bed rails, tray tables, IV poles and
nurse call buttons with antimicrobial copper versions. The rooms with copper
surfaces demonstrated a 97% reduction in surface pathogens, which is the same
level achieved by terminal cleaning, a process conducted after a patient vacates a
room. A study conducted in the United States over four-years has shown that the
use of antimicrobial copper surfaces in hospital rooms can reduce the number of
28 [ONLINE] Available at: http://web.b.ebscohost.com.newington.idm.oclc.org/ehost/pdfviewer/
pdfviewer?sid=dbaebc08-7ad3-4341-910c-3ae3a0f24740%40sessionmgr198&vid=1&hid=128. [Accessed
18 August 2015].
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health care acquired infection (HAIs) by 58% when compared to rooms without
copper surfaces29. The study also confirmed that antimicrobial copper surfaces
could continuously kill 83% of bacteria that cause HAIs with two hours,
including drug resistant “superbugs”. The idea that copper inhibits bacterial
growth is further backed in a cross-over study published by the US National
Centre for Biotechnology Information, which found that copper surfaces in a
medical ward harboured between 90% and 100% lower median numbers of
microorganisms. Among these studies, other extensive studies have also been
conducted in Japan, South Africa, Chile, and United Kingdom & Ireland. While
these studies have been conducted with different aims and methods, all of them
show evidence that copper can inhibit bacterial growth.
Application of copper in clinical environments
Worldwide, HAIs are a major and growing problem. In Australia around 9000
people die form health related infections each year. While copper has been
linked with antimicrobial properties, recent studies have concluded that copper
can reduce the risk of acquiring a health care related infection. The reduction of
picking up HAIs would save lives and cut healthcare costs. The primary
installation of copper in hospitals would most likely be more expensive than
traditional surfaces such as plastic. However, studies have shown that some
hospitals are underfunded to deal with infection. According to the World Health
Organization, healthcare facilities around the world, seven million infections
occur every year and cost more that $80 billion globally. By reducing the risk of
infections, overtime the cost of installing copper surfaces would be offset by the
costs saved when risk of infections are reduced, which is to not exclude the fact
that many lives would be saved in the process. Antimicrobial copper surfaces
and products are currently being manufactured worldwide. An increasing
number of aged care facilities, medical clinics and hospitals are employing the
use of these copper products as part of various infection control strategies.
Equipment:29 [ONLINE] Available at: http://web.b.ebscohost.com.newington.idm.oclc.org/ehost/pdfviewer/pdfviewer?
sid=1e7802be-ffc9-492d-b95d-7948c4b7c0fb%40sessionmgr110&vid=1&hid=128. [Accessed 18 August 2015].
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Item Number requiredCopper Tubing (15cm) 1Stainless Steel Tubing (15cm) 1PVC Tubing (15cm) 1Agar Plates 27Beakers (250ml) 12Beakers (1L) 2Retort Stand with Boss Head Clamp 3Distilled Water 2LSterile Swabs Pack of 10070% Alcohol Solution 500mlStopwatch 1Sharpie 1Sticky Tape 1 rollPencil 1Ruler (15cm) 1Thermometer 1Scissors 1Glass Stirring Rod 1Detergent 50mlGlass Jar (Height>15cm, Diameter>8cm) 1Pipets 20Bacteria E-ColiLatex gloves 4Safety glasses 1Glass pipette (6ml) 1Glass pipette (1ml) 1Bunsen burner 1Matches 1 boxInoculation loop 2
Hypothesis:The copper in comparison to the stainless steel and PVC should have a much
lower CFU/ml count when the agar plates are cured and the bacteria allowed to
grow. This would not only show that copper is a effective antimicrobial agent, it
would show that in comparison with commonly used materials in hospitals such
as plastic and stainless steel surfaces, copper is more effective in killing bacteria
which may reduce the risk of healthcare- associated infections (HAI). This
property of copper would be a reason why it would have practical applications in
clinical environments such as hospitals in reducing HAIs.
Variables:
Controlled Variables
- Temperature of distilled water
- Time the tubing is allowed to set in the bacterial solution
- Time intervals at which swabs are taken at
Independent Variables
17
- Concentration of the bacterial solution
Dependent Variables
- Amount of viable bacteria on the three types of surfaces
Controls to be tested:
- Bacterial solution without any contact with external surfaces such as
swabs30
- Swabs themselves (This is to see how sterile they are)
Procedure:
Initial Preparation/sterilization of tubing:
1. Mark a horizontal line 5cm from the bottom of each tube, see fig.1 for
reference
Fig.1
2. Fill the glass jar with distilled water until it is about 75% full
3. Pour detergent into the distilled water
4. Use the glass stirring rod to stir the mixture until the detergent and the
water have mixed, i.e. there should not be any “globs” of detergent in the
solution
5. Put all three tubes into the glass jar, and then proceed the fill the glass jar
with distilled water until the tubes are submerged, screw the top back
onto the jar
6. Leave the tubes in the detergent solution for two hours
30 2015. . [ONLINE] Available at:http://www.epa.gov/oppad001/pdf_files/test_meth_residual_surfaces.pdf. [Accessed 25 June 2015]
The marked lines5cm
18
7. After two hours take the three tubes out of the solution and thoroughly
wash under a running tap until all residue of the detergent solution has
been washed off
NB- the tubes do not need to be dried
8. Put the tubing in a clean 250ml beaker with the bottom of the tubes
touching the bottom of the beaker as shown in fig.2
Fig.2
9. Fill the beaker with 160ml 70% alcohol
10. Label this beaker “Alcohol”
11. Leave the tubing in the alcohol for 10 minutes
12. After 10 minutes, put each individual tube in a retort stand with the
bottom of the tubing facing down, and as shown in fig.3
Fig.3
Note the position of the marked lines
The bottom of the tubes touching the bottom of the beaker
19
13. Move the retort stand so that the tubes are overhanging a sink or basin as
shown in fig.4
NB- At this stage the 250ml beaker labeled with “Alcohol” should be put
aside and covered with Cling Wrap, or a paper towel to prevent the
alcohol from evaporating
Fig.4
14. Let the tubes dry for 10min
Carrying out the experiment
15. Put on gloves and safety glasses
16. Fill a 6ml glass pipet with 5ml of the E-Coli broth
17. Release the 5ml of E-Coli broth into a 500ml beaker
18. Fill the 1L beaker until the it is 500ml full with distilled water by tilting
the beaker on its side and then pouring the water down its side as shown
in fig.5
Fig.5
The marked line should be “hanging” downward
20
19. When the beaker is about 450ml full use a squirt bottle filled with
distilled water to gradually fill the beaker up to the 500ml mark, this is
your bacterial solution
20. Light a Bunsen burner and flame an inoculating loop as shown in fig.6
NB- the inoculating loop should be held above the tip of the blue flame as
this is where it is the hottest
Fig.6
21. Wait about 30sec for the inoculating loop to cool down before using it to
stir the bacterial solution to ensure that the bacterial broth is mixed with
the distilled water
22. After you have stirred the solution, flame the inoculating loop once again
to sterilize it
23. Gently pour 150ml of the bacterial solution into three beakers, after this
you should have 50ml of the solution left in the 1L beaker
24. Cover the 4 beakers with cling wrap to prevent contamination and set
them aside
21
25. Get 5 agar plates
26. Divide the first three agar plates into 3 equal sections
27. Label the three sections in each agar plate “5min”, “10min” and “20min”,
as shown in fig.7
Fig.7
28. Near the edge of the three plates, label them as which test they are, the
surface from which swabs are taken from and the dilution factor, i.e. For
the FIRST test you would label the plates, “Test 1 Dilution factor 10-2”, and
then label the plates “Copper”, “Steel” and “PVC”, an example can be seen
in fig.8, these are your “Agar plates to test surfaces”
Fig.8
29. Label one other plate “Control test: Swab only” and another plate “Control
test: Bacterial solution only”
30. Select a random swab from the pack of 100 swabs and streak the agar
plate labeled “Control test: Swab only” in a “zigzag” pattern as shown in
fig.9
Fig.9
22
31. Seal this agar plate with sticky tape
32. Get the 1L beaker with the remaining 50ml bacterial solution in it, remove
the cling wrap and pour about 10 drops into the agar plate labeled
“Control test: Bacterial solution only”
33. Close the plate and “swish” the bacterial solution around in the agar plate
by moving the plate in a figure eight pattern.
34. Seal this agar plate with stick tape
35. The 1L beaker should be disposed by giving it to a teacher or supervisor
for sterilization
36. Set up the three 250ml beakers with the bacterial solution and the three
retort stands with the clean tubing as shown in fig.10
Fig.10
37. Lower the tubing into the bacterial solutions so that the bottom of the
tubes sit on the bottom of the beakers as shown in fig.11, leave the tubes
in the solution for 10 min
Fig.11
23
38. After 10 min raise the tubes above the beakers as shown in fig.12, start
the stopwatch
Fig.12
39. When the stopwatch has reached 5 min, i.e. the tubes have dried for 5
minutes, take swabs of the three surfaces and streak the respective agar
plates in the 5 min section, i.e. a swab taken from the copper surface
should be streaked on the 5 min section in the agar plate labeled
“Copper”, swabs should also be streaked in a zigzag pattern, as shown in
fig.13 (next page)
NB- Swabs should be taken from an area below the marked line
- Used swabs should be put into a clean beaker for disposal once the
experiment is completed
Fig.13
24
40. When the stop watch has reached 10 min, take a swab of all three surfaces
again and streak the swabs in the “10min” section on the respective agar
plates
41. When the stopwatch has reached 20min, take a swab of all three surfaces
and streak the swabs in the “20min” section on the respective agar plates.
42. Seal all three agar plates with sticky tape
43. Put the 5 agar plates into an incubating oven
44. Detach the three tubes and put them in the beaker labeled alcohol to
sterilize them
45. Repeat steps 11-44, however the “Agar plates to test surfaces”, should be
labeled “Test 2 Dilution factor 10-2”
46. Repeat steps 11-44, however the “Agar plates to test surfaces”, should be
labeled “Test 3 Dilution factor 10-2”
47. Repeat steps 11-46 with a dilution factor of 10-3, i.e. only 0.5ml of the E-
Coli broth should be put into the bacterial solution
Risk Assessment:
Risk Risk reduction Accident responseE-Coli bacteria can be easily
spread if contact with it
occurs, this will cause
health issues and is a major
problem is it is wide spread
All surfaces and objects
should be sterilised before
and after use. Personal
protective equipment
(PPE) such as latex gloves
should be used throughout
the whole experiment.
Isolate affected areas as
well as people. A
professional biohazard
clean-up organisation
should be contacted to
safely clean contaminated
surfaces and to help treat
25
affected people.
E-Coli can grow to
hazardous levels once
incubated, if spores have
formed, opening the agar
plate it is inoculated on
may result in E-Coli
bacteria becoming air born.
Once incubated, agar plates
inoculated with E-Coli
bacteria should not be
opened.
Immediately isolate the
affected area and turn off
systems such as air-
conditioning, which may
disturb the air. A
professional biohazard
clean-up organisation
should be contacted to
safely clean contaminated
surfaces and to help treat
affected people.
Results:For dilution factor 10-2, refer to appendix for pictures of tests
Test #1 Dilution factor: 10-2
Time after tubing has been lifted out of bacterial solution (min)
Copper (CFU)
Stainless Steel (CFU)
PVC (CFU)
5 N/A 31 1110 N/A 26 920 N/A 21 8
Test #2 Dilution factor: 10-2
Time after tubing has been lifted Copper Stainless Steel PVC (CFU)
26
out of bacterial solution (min) (CFU) (CFU)5 60 176 78
10 41 152 7020 1 126 58
Test #3 Dilution factor: 10-2
Time after tubing has been lifted out of bacterial solution (min)
Copper (CFU)
Stainless Steel (CFU)
PVC (CFU)
5 71 98 7210 19 16 6620 1 81 59
Test #1 Dilution factor: 10-3
Time after tubing has been lifted out of bacterial solution (min)
Copper (CFU)
Stainless Steel (CFU)
PVC (CFU)
5 0 0 010 0 0 020 0 0 0
Test #2 Dilution factor: 10-3
Time after tubing has been lifted out of bacterial solution (min)
Copper (CFU)
Stainless Steel (CFU)
PVC (CFU)
5 0 0 010 0 0 020 0 0 0
Test #3 Dilution factor: 10-3
Time after tubing has been lifted out of bacterial solution (min)
Copper (CFU)
Stainless Steel (CFU)
PVC (CFU)
5 0 0 010 0 0 020 0 0 0
Calculations:
CFU/ml=
Test #1- Stainless Steel- Dilution factor 10-2- 5 minute
CFU/ml=
Test #1- Stainless Steel- Dilution factor 10-2- 10 minute
CFU/ml=
27
Test #1- Stainless Steel- Dilution factor 10-2- 20 minute
CFU/ml=
Test #1- PVC- Dilution factor 10-2- 5 minute
CFU/ml=
Test #1- PVC- Dilution factor 10-2- 10 minute
CFU/ml=
Test #1- PVC- Dilution factor 10-2- 20 minute
CFU/ml=
Test#2- Copper- Dilution factor 10-2- 5 minute
CFU/ml=
Test#2- Copper- Dilution factor 10-2- 10 minute
CFU/ml=
Test#2- Copper- Dilution factor 10-2- 20 minute
CFU/ml=
Test#2- Stainless Steel- Dilution factor 10-2- 5 minute
CFU/ml=
Test#2- Stainless Steel- Dilution factor 10-2- 10 minute
CFU/ml=
Test#2- Stainless Steel- Dilution factor 10-2- 20 minute
CFU/ml=
Test#2- PVC- Dilution factor 10-2- 5 minute
28
CFU/ml=
Test#2- PVC- Dilution factor 10-2- 10 minute
CFU/ml=
Test#2- PVC- Dilution factor 10-2- 20 minute
CFU/ml=
Test#3- Copper- Dilution factor 10-2- 5 minute
CFU/ml=
Test#3- Copper- Dilution factor 10-2- 10 minute
CFU/ml=Test#3- Copper- Dilution factor 10-2- 20 minute
CFU/ml=
Test#3- Stainless Steel- Dilution factor 10-2- 5 minute
CFU/ml=
Test#3- Stainless Steel- Dilution factor 10-2- 10 minute
CFU/ml=
Test#3- Stainless Steel- Dilution factor 10-2- 20 minute
CFU/ml=
Test#3- PVC- Dilution factor 10-2- 5 minute
CFU/ml=
Test#3- PVC- Dilution factor 10-2- 10 minute
CFU/ml=
Test#3- PVC- Dilution factor 10-2- 20 minute
CFU/ml=
29
Analysis:Outliers (anomalies) are not included in average CFU/ml calculations.
Surface: Copper Dilution factor: 10-2
Time after tubing has been lifted out of bacterial solution (min)
Test #1 (CFU/ml)
Test#2 (CFU/ml)
Test#3 (CFU/ml)
Average CFU/ml
5 N/A 6000 7100 710010 N/A 4100 1900 300020 N/A 100 100 100
Surface: Stainless steel Dilution factor: 10-2
Time after tubing has been lifted out of bacterial solution (min)
Test #1 (CFU/ml)
Test#2 (CFU/ml)
Test#3 (CFU/ml)
Average CFU/ml
5 3100 17600 9800 1016710 2600 15200 1600 890020 2100 12600 8100 7600
Surface: PVC Dilution factor: 10-2
Time after tubing has been lifted out of bacterial solution (min)
Test #1 (CFU/ml)
Test#2 (CFU/ml)
Test#3 (CFU/ml)
Average CFU/ml
5 1100 7800 7200 536710 900 7000 6600 483420 800 5800 5900 4167
No bacteria grew on the agar plates when the dilution factor of the bacterial
solution was 10-3. This result will be discussed in the discussion section.
30
Test # 1 Test # 2 Test # 30
1000
2000
3000
4000
5000
6000
7000
8000
9000
PVC Surface
5 minutes10 minutes20 minutes
Am
oun
t of
via
ble
bac
teri
a on
su
r-fa
ces
(CFU
/ml)
5 10 200
2000
4000
6000
8000
10000
12000
Average CFU/ml on Surfaces after tubes have been unsubmerged
Stainless SteelPVCCopper
Time after tubing has been raised out of bacterial solution (minutes)
Am
oun
t of
via
ble
bac
teir
a on
su
rfac
es
(CFU
/ml)
Test #1 Test #2 Test #30
1000
2000
3000
4000
5000
6000
7000
8000
Copper surface
5 minutes10 minutes 20 minutes
Am
oun
t of
via
ble
bac
teri
a on
su
r-fa
ces
(CFU
/ml)
31
25%
75%
Surface: Stainless SteelAmount of Viable Vacteria Killed from 5-minute Mark to
the 20-minute Mark
% of Bacteria Killed% of Viable Bacteria still remaning
23%
77%
Surface: PVCAmount of Viable Vacteria Killed from 5-minute Mark to
the 20-minute Mark
% of Bacteria Killed% of Viable Bacteria still remaning
98%
2%
Surface: CopperAmount of Viable Bacteria Killed from 5-minute Mark to
the 20-minute Mark
% of Bacteria Killed% of Viable Bacteria still remaning
32
Discussion
Trend in results
The second and third tests when the dilution factor was 10 -2 were carried out a
day after the first test was conducted. The results show that the first test had a
considerably lower CFU/ml with an average of 1766, when compared to the
second and third tests, which had averages of 8466 and 5838 respectively. The
most likely reason for this result is that when the bacterial solutions were left
overnight, the bacteria had a chance to reproduce. This would have increased
bacterial concentration of the bacterial solutions, i.e. there are greater numbers
of E-Coli in the solutions. As the amount of bacteria in the second and third test
killed by the surfaces would most likely remain the same as the first test, the
reason that a substantial increase in the number of viable bacteria on the three
surfaces has occurred, can be linked with higher amounts of bacteria in the
bacterial solutions when the tests were taken.
During the second test for Stainless Steel when the dilution factor was 10-2, an
abnormally large amount of water residue was observed on surface when
compared to all other tests conducted at that time. The results show that when
the agar plates were cultured this particular test had a significantly increased
CFU/ml count. As bacteria are so small, the water residue can contain millions of
bacteria cells. The main reason as to why there was an increased CFU/ml count
in this test was that the increased water residue suspended the E-Coli bacteria in
33
an aqueous solution, which not only provided a moist environment, which
encourages bacterial growth, but also prevented a vast majority of the bacteria
from coming into contact with copper surface. Referring to the background
information, in general, bacteria that are not in contact with the copper surface
are not killed.
When the dilution factor was 10-2, in all three tests for the Stainless Steel and PVC
surfaces the amount of viable bacteria present, declined at a slower rate when
compared to the copper surface. For the Stainless Steel surface and the PVC
surface, the amount of viable bacteria declined by an average of 2567 and 3600
from the 5-minute mark to the 20-minute mark. In comparison, the amount of
viable bacteria on the copper surface declined by an average of 6450 from the, 5-
minute mark to the 20-minute mark, which is more than a 160% increase than
its closest competitor which was the PVC surface. Furthermore, the percentage
decrease of viable bacteria taken from the 5-minute mark and compared with the
20-minute for the Stainless Steel and PVC surfaces was only 25.25% (4sig.fig.)
and 22.36% (4sig.fig.). However, the copper surface had a percentage decrease of
98.47% (4sig.fig). The decrease in viable bacteria on all three surfaces would
have been caused by factors such as the surface drying out. However, the
significant percentage decrease on the copper surface, would not have only been
caused by the surface drying out, as if it was the case then either the other two
surfaces would have had a percentage decrease similar to that of the copper
surface, or the copper surface would have had a percentage decrease similar to
that of the other two surfaces. From this result it can be concluded that there is
another factor involved in the killing of bacteria on the copper surface.
The tests conducted when the dilution factor was 10-3, did not show any bacterial
growth. While this result is undesirable it shows that the less bacteria there is in
an area, the lower the survival rates of the bacteria. This concept in addition with
copper’s ability to limit and reduce bacterial growth provides firm grounding for
its applications in clinical health care environments.
34
From the results and the background information (refer to “Actual studies
conducted”), this experiment has shown that copper can reduce the risk of
acquiring health related infections. The process by which copper does this can be
shown as follows:
Copper kills bacteria Bacterial growth is not only limited, but reduced
Lower numbers of bacteria present in an area mean that there is less of a chance
of bacteria surviving and remaining on surfaces in that area Less bacteria on
surfaces in an area results in a lowered risk of acquiring infections
Sources of error
After the agar plates were cured, some plates had some mould growth. This
means that either the plates were contaminated during the preparation process
of the agar plates or that the plates were contaminated during the inoculation
process when the agar plates were being streaked with the swabs. The chance of
contamination in the inoculating process could be reduced by working under a
laminar flow. Tests where the dilution factor was 10-2 were not conducted under
a laminar flow due to lack of knowledge. However, after further research
regarding aseptic technique, tests run where the dilution factor was 10-3
incorporated this technique. Evidence for working under a lamina flow actually
reducing contamination can be seen in these two agar plates.
An agar plate not inoculated under a lamina flow An agar plate inoculated under a lamina flow
35
The bacterial colonies growing in the agar plate what was not inoculated under a
lamina flow can be identified as E-Coli colonies by comparing them to one of the
controls, which was conducted by directly pouring the bacterial solution onto an
agar plate. The colonies in the control are similar to the colonies growing in the
example on the previous page in terms of shape and colour, which for this
project is enough to say that those colonies in the agar plate not inoculated
under a lamina flow are indeed E-Coli colonies
A control inoculated with the E-Coli bacterial solution only
The reason why working a laminar flow would reduce the risk of contamination
is that the air around a flame rises, i.e. hot air rises. There are mould particles in
the air around us and when this experiment is conducted in such an environment
there is always the risk that some mould particles or other contaminants may
“fall” into the agar plates. By causing the air around the agar plate to rise,
contaminants are “pushed” upwards, which reduces the chance of a contaminant
falling into the agar plate.
Another mistake that could have been made is that the surfaces were not
swabbed in the same area for the same test, i.e. when the timer counts to 5
minutes a swab is taken, however when it counts to 10 minutes a swab is taken
from the other side of the tubing. This may affect results as different areas may
Mould growing on the agar plate
36
have varying amounts of moisture on them. As written in the background
knowledge section, moist areas promote more bacterial growth than dry areas.
This may account for the 3rd test for stainless steel when the dilution factor was
10-2, where the CFU/ml was significantly lower at 10 minutes than at 20minutes.
In this case there an obvious mistake has occurred, as usually, on dry surface
bacteria numbers will decline over time instead of increase. Here, a swab for the
10-minute section may have been accidentally taken from an area that dried out
in the first few minutes, but was not swabbed for the 5-minute section or the 20-
minute section.
After the agar plates had been incubated, some of the plates were completely
dried out. Such is the case with the 1st test for copper when the dilution factor
was 10-2, where due to the agar drying out, no results were able to be obtained
regarding bacterial growth save for the fact that dry conditions do not encourage
bacterial growth. A possible cause of the agar plates drying out may be due to the
layer of agar not being poured thick enough, which is a human error.
The contamination of some of the agar plates was also partly due to a scientific
error. The amount of contaminants such as mould particles in the air could not
be controlled in the environment that these tests were carried out in. However,
this error can be avoided by working in a sterile environment such as a structure
with air locks, which requires multiple sterilisation stages before entry can be
granted. This measure would not be practical for this project due to the cost
factors involved.
Some bias also occurred in the experiment. Due to a lack of materials, bacterial
solutions were used repetitively, which may have affected the amount of bacteria
present in the solutions. This would affect results as, by lowering the amount of
bacteria in a solution, the bacteria may be killed in greater numbers. Evidence for
this rational can be seen in the background research section.
Reliability, validity, and accuracy of data
37
The data in this experiment was made reliable by repeating the experiment
multiple times. All data obtained in this experiment was reliable as all except two
results followed a general trend, i.e. data for the Copper, Stainless Steel, and PVC
surface, followed individual trends for the respective surfaces. The general trend
was that as the time period, in which the surfaces were unsubmerged, increased,
the CFU/ml on the surfaces decreased. Of the two anomalies the first was that
the agar plate containing the first test for the copper surface when the dilution
factor was 10-2 had completely dried up in the incubating oven. However, just
because no bacterial growth could be observed, it does not show that there was
no bacterial growth at all. Perhaps there was some bacterial growth but it
disappeared after the agar dried out. The second anomaly was the swab taken at
the 10-minute mark for the third test of Stainless Steel when the dilution factor
was 10-2.
The validity of the data collected in this experiment was affected by one main
factor, the repeated use of bacterial solutions. Due to a lack of materials a
bacterial solution could not be made for each individual test. As a result the same
bacterial solution had to be used for three tests, i.e. the bacterial solution with a
dilution factor of 10-2 was used for three tests before being disposed of. After the
initial use of the bacterial solutions, there may be different amounts of bacteria
in the solutions themselves. This would decrease the validity of the experiment
as during the second and third use of the bacterial solutions, different amounts of
bacteria would be being put onto the surfaces. A possible reason as why there
would be different amounts of bacteria in the solutions would be that, for
example in the case of copper it may kill more bacteria while it is submerged in
the E-Coli solution than the Stainless Steel surface or the PVC surface.
As there are no set results (“real results”, an example being Acceleration due to
gravity), to compare this experiment with, it would not be appropriate to
comment on the accuracy of the data collected.
Future Studies
38
This experiment could be further extended by testing a wider range of bacteria in
a wider range of dilutions, i.e. 10-1, 10-1.2, 10-1.4, 10-1.6, 10-1.8, 10-2, 10-2.2. With the
different types of bacteria, antibiotic resistant bacteria such as MRSA could be
tested to see if the effect of copper was different between antibiotic resistant
bacteria and non-antibiotic resistant bacteria. Copper alloys with different
percentages of copper could also be tested to see which percentage of copper
was most effective in limiting bacterial growth and was most cost effective.
Conclusion:
From these results and the discussion a conclusion can be reached, which is that,
copper can be used as an antimicrobial agent to limit bacterial growth. These
results also show that copper has practical applications in clinical healthcare
environments such as hospitals, as by lowering the amount of bacteria present,
you lower the risk of infections.s
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Appendix:
Glossary of terms
Convection current- a current in which warm air rising and cooler falling
Bactericide- substance that kills bacteria
Phospholipid- a class of lipids that are a major component of all cell membranes
Solutes- substance dissolved in another substance known as a solvent
Extrachromosomal DNA- DNA found outside of the nucleus that are not required
to perform day to day functions but have important biological functions
Subunit- A subdivision of a larger unit
Haber-Weiss and Fenton reaction- A reaction in which hydroxyl radicals are
produced
Macromolecules- Very large molecules commonly created by the merging of
smaller subunits
Lipid peroxidation- A process in which free radicals cause cell damage, resulting
in the oxidative degradation of lipids
Metalloproteins- A protein that contains metal ions as a cofactor
HCAI- Health Care Associated Infections
Desiccating- the removal of moisture from something
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