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  • MICROBIOLOGY . 4 :Lec 1
  • Burton's Microbiology for the Health Sciences Chapter 4. Microbial Diversity Part 1: Acellular and Procaryotic Microbes
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  • Acellular Microbes Viruses Complete virus particles are called virions. Most viruses are from 10 to 300 nm in diameter. Viruses infect humans, animals, plants, fungi, protozoa, algae and bacterial cells. 4
  • Viral structure A typical virion consists of a genome of either DNA or RNA, surrounded by a capsid (protein coat) which is composed of protein units called capsomeres. Some viruses (enveloped viruses) have an outer envelope composed of lipids and polysaccharides. 5
  • Viruses have 5 properties that distinguish them from living cells: 1. They possess either DNA or RNA living cells possess both. 2. They are unable to replicate on their own. 3. Do not divide by binary fission, mitosis, or meiosis. 4. They lack the genes and enzymes necessary for energy production. 5. They depend on the ribosomes, enzymes, and metabolites of the host cell for protein and nucleic acid production. 6
  • Viruses are classified by: Type of genetic material (either DNA or RNA) Shape and size of capsid Number of capsomeres Presence or absence of an envelope Type of host it infects Disease it produces Target cell(s) Immunologic/antigenic properties 7
  • virus DNA Single-strand 8 Double-strand RNA Single-strand Double-strand
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  • Herpesviruses acquiring their envelopes as they leave a host cells nucleus by budding. Copyright 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins 12
  • FIGURE 4-4. Virus particle becoming enveloped in the process of budding from a host cell. 13
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  • Comparative sizes of virions, their nucleic acids, and bacteria. 15
  • Bacteriophages Viruses that infect bacteria are known as bacteriophages. There are two categories of bacteriophages: virulent bacteriophages and temperate bacteriophages. Virulent bacteriophages always cause the lytic cycle, which ends with the destruction of the bacterial cell. 16
  • Lytic process A partially lysed cell of Vibrio cholerae with attached virions of phage CP-T1. 17
  • Bacteriophages. The bacteriophage T4 is an assembly of protein components. 20 facets, filled with DNA Copyright 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins 18 Viral DNA enters the cell through the core.
  • Multiplication of animal viruses Animal viruses escape from their host cells either by lysis of the cell or budding. Viruses that escape by budding become 19 enveloped viruses.
  • Latent Virus Infections Viral infections in which the virus is able to hide from a hosts immune system by entering cells and remaining dormant. 20 Herpes viral infections are examples.
  • Antiviral Agents Antibiotics are not effective against viral infections. Antiviral agents are drugs that are used to treat viral infections. These agents interfere with virus-specific enzymes and virus production by disrupting critical phases in viral multiplication or inhibiting synthesis of viral DNA, RNA, or proteins. 21
  • Acellular Microbes, cont. Oncogenic Viruses Viruses that cause cancer. Examples include Epstein-Barr virus, human papillomaviruses, and HTLV-1. Human Immunodeficiency Virus (HIV) 22 The cause of acquired immunodeficiency syndrome (AIDS). It is an enveloped, single-stranded RNA virus. The primary targets for HIV are CD4+ cells. CD4+ cells = T-helper cells = WBC
  • Human Immunodeficiency Virus (HIV) 23
  • Viroids and Prions Viroids and Prions (smaller and less complex infectious particles than viruses) Viroids Viroids are short, naked fragments of single-stranded RNA, which can interfere with the metabolism of plant cells. Viroids are transmitted between plants in the same manner as viruses. 24
  • Prions Prions are small infectious proteins that cause fatal neurologic diseases in animals; examples: Scrapie, Bovine Spongiform Encephalopathy (Mad Cow Disease) and Creutzfeldt-Jacob disease. Of all pathogens, prions are the most resistant to disinfectants. 25
  • Bacteria
  • The Domain Bacteria Characteristics Bacteria are divided into 3 major phenotypic categories: 1. Those that are Gram negative and have a cell wall 2. Those that are Gram positive and have a cell wall 3. Those that lack a cell wall (Mycoplasma spp.) 27 Characteristics of bacteria used in classification and identification include: cell morphology, staining reactions, motility, colony morphology, atmospheric requirements, nutritional requirements, biochemical and metabolic activities, enzymes that the organism produces, pathogenicity, and genetic composition.
  • Cell Morphology There are 3 basic categories of bacteria, based on shape: 28 Cocci (round bacteria) Bacilli (rod-shaped bacteria) Curved and spiral-shaped bacteria
  • Cocci Cocci is round bacteria may be seen singly or in pairs (diplococci), chains (streptococci), clusters (staphylococci), packets of 4 (tetrads), or packets of 8 (octads). The average coccus is about 1 m in diameter. Some cocci have coccus in their name. 29
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  • Morphologic Arrangements of Cocci Gram-positive Staphylococcus aureus in clusters. 31 Streptococcus mutans illustrating cocci in chains.
  • Diagram Showing Various Forms of Bacteria That Might be Observed in Gram-Stained Smears 32
  • Bacilli Bacilli 33 They may occur singly, in pairs (diplobacilli), in chains (streptobacilli), in long filaments, or branched. Often referred to as rods; may be short or long, thick or thin, and pointed or with curved or blunt ends. An average sized bacillus is 1 x 3 m. Extremely short bacilli are called coccobacilli. Examples of medically important bacilli: Escherichia, Klebsiella, and Proteus spp, Pseudomonas, Haemophilus, and Bacillus spp.
  • Curved, Spiral-Shaped Bacteria Curved and Spiral-Shaped Bacteria Examples of curved bacteria: Vibrio spp. Campylobacter spp. Helicobacter spp. Examples of spiral-shaped bacteria: Treponema spp. Borrelia spp. 34
  • Staining Procedures Three Major Categories of Staining Procedures 1. 2. Simple stains Structural staining procedures Spore stains 3. Capsule stains Flagella stains Differential staining procedures 35 Gram and acid-fast staining procedures
  • Staining Procedures, cont. Bacterial smears must be fixed prior to staining The fixation process serves to: 1. 2. 3. kill organisms, preserve their morphology, shape anchors the smear to the slide The two most common types of fixation: 1. Heat-fixation; not a standardized technique; excess heat will distort bacterial morphology 2. 36 Methanol-fixation; a standardized technique; the preferred method
  • Simple Bacterial Staining Technique 37
  • The Gram Staining Procedure Divides bacteria into 2 major groups: Gram-positive (bacteria are blue-to-purple) Gram-negative (bacteria are pink-to-red) The final Gram reaction (positive or negative) depends upon the organisms cell wall structure. The cell walls of Gram-positive bacteria have a thick layer of peptidoglycan, making it difficult to remove the crystal violet-iodine complex. Gram-negative organisms have a thin layer of peptidoglycan, making it easier to remove the crystal violet; the cells are subsequently 38 stained with safranin.
  • Gram Staining 39