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3.growth and nutrition of bacteria

Bacteria like all cells, require nutrients for the maintenance of their metabolism and for cell division.

Fast growing bacteria divide approximately every 30 mins.

Chemically, bacteria consist of; protein, polysaccharide, lipid, nucleid acid , peptidoglycan .

Bacterial growth requires;

1.materials for the synthesis of structural components and for cell metabolism

2.energy

Bacteria differ widelyin their nutritional requirements. Some bacteria can syntesise all they requirefrom the simplest elements. Other including most pathogenic bacteria are unable to do this; they

need a ready made supply of some of the organiccompounds required for growth; other necessary

compounds can be syntesised from breakdown product of compleks macromolecules (eg, proteins,

nucleic acids) wich are taken into the cell and degraded by bacterial enzymes. This is illustrated

diagrammatically in figure.

Elements. Bacterial structural component and macromelocules for cell metabolism are

syntethesised from the elements shown in table 3.1. all are therefore necessary for bacterial growth

whether available simply as elements or as part of complex molecules.

The four most important elements are;

1.hydogren, oxygen,carbon, nitrgen

*hydrogen and oxygen

These are obtained from water essential for the growth and maintenance of any cell; water must

therefore be available in any situation 0f patential bacterial growth.

*carbon and nitrogen

Carbon and nitrogen are the principal elements for wich an external source must be foud .

Depending on their requirements, bacteria can be classified as;

1.autrotrophs; free-living, non parasitic bacteria, most of wich can use carbon dioxide as their

carbon source. The energy needed for their metabolism can be obtained from;

a.sunlightphotoautotrophs

b.heterotrophs; generally parasitie bacteria ; require more complex , organic compounds than

carbon and energy . sugars.

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Human phatogenic bacteria are heterotrophs; they are parasitic and have evolved to adapt

to an environment. The humman body in wich many of their nutrients are ready made in complex

form and freely available. Such bacteria have lost the biosynthetic mechanism necessary for a free-

living existence in a harsher anvironment , soil or water.

The principal source of carbon is carbohydrate sugars are degraded either by; 1.oxidatin 2.

Fermentation this provides energy in the form of adenosine triphosphate(atp)the universal enrgy

storage compound.The main source of nitrogen is ammonia ,usually in the form of an ammonium

salt; this is available either in the enviroment or produced by the bacterium as a result of amino

acids released from proteins.

*organic growth factors

These are organic compounds that cannot by synthesised by many bacteria; an exogenous supply is

therefore required. Although olten only in small amountts.

Some example are listed below;

1. Amino acids; required by many bacterial species which cannot synthesise them fromsimpler elements. Bacteria posses enzymes that degrade proteins to amino acids, these then

form an intracellular poll from which require the appropriate amino acid is withdrawn to

become incorporated into bacterial proteins,,

2. Purines and pyrimidines; the precursors of nucleic acids and coenzymes. In bacteria whichrequire them. They are converted into nucleosides and nucleotides before incorporation

into DNA and RNA.

3. Vitamins , many pathogenic bacteria lack ability to synthesise vitamins most of wich arerequired for the formation of coenzymes.

*prototrophs and auxotrophs

Prototrophs are wild type bacteria with normal growt requirement . auxototrophs are mutant

which require an additional growth factor not needed by the parentel or wild type strain ; the

growth factor may be different types of chemical compound , e,g. An amino acid. Pyrimidine

base.vitamin..

*NUTRIENT UPTAKE

Most nutrients are small molecules which diffuse freely across the bacterial cytoplasmic membrane

to enter the cell; some are at a higher concentration within the bacterial cell than in the external

environment , so that their uptake is an energydependent process. Sugars are nutrients of

relatively large size and therefore diffuse slowly into bacterial cell. Enzymes which facilitate of larger

nutrient molecules are present in many bacteria. Usually associated with the cell membrane and

energy dependent, the may be;

1, inducible produced only in the presence of the substrake, or

2, constitutive- prodused constantly and independently of the substrate

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ENVIRONMENTAL CONDITIONS GOVERNING GROWTH

1.WATER

Moisture is an absolute requirement for the growth of all bacteria. At least 80% of the bacterial cell

consist of water. The availability of water,for example, largely determines the size of that can be

supported by the skin.

2.oxygen

Bacteria differ in their need for molecular oxygen for growth or in the case of anaerobic bacteria

in their need for its exclusion ; this is illustrated in table 3.2.

3.carbon dioxide

Required by all bacteria and usually available as a product of metabolism. Slow growing or fastidious

organism may not generate enough carbon dioxide so that this muts be supplied exogenously; this

requirement becomes increased by environmental change , e,g.caused by the transfer of bacteria

from growth in vivo to culture in vitro.

Many pathogenic bacteria therefore require addition of 5-10% carbon dioxide to the

incubator atmosphere for primary isolation in vitro from clinical material.

4.temperature

Bacteria also differ with regard to the optimal temperature range for their growt;

Pasychrophile.........below 20 c

Mesophile .............between 25c and 40c

Thermophile ........between 55c and 80c

Most medically important species are mesophiles and grow best at temperatur around 37c.

5.hydrogen ion concentration

Not surprisingly, the optimal Ph for bacteria that have evolved in assciation with man is similar tophysiological Ph,i.c. pH 7.2. 7.4. A few species have evolved to become adapted to ecological

niches where the ph is either higher or lower than normal.

6.bacterial growth and division

Bacterial growth is the result of balanced increase in the mass of cellular constituents and structures

; the biosynthetic processes on wich this increase depends are fuelled by energy , usually from atp.

Cell division is initiated when the increase in cellular constituens and struktures reaches a

critical mass.

Bacteria divide by binary fission

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Bacteria chromosome; a circular double stranded DNA molecule . it replicates

semiconservatively and bidirectionally; the replicated genome segregates between the daughter

cells ; cross walls then form as the parent cell divides into the two daughter cells.s