1. Chapter 37 Introduction to Microbiology
Microbiology Unit 7
Chapter 37
Introduction to Microbiology
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2. Microbiology Basics
A basic understanding of the characteristics of bacteria, fungi, and viruses will aid the veterinary technician in collection, handling, and evaluation of samples
Identification of bacterial, fungal, and viral pathogens is the primary purpose of microbiologic examinations
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3. Bacterial Cell Morphology
Prokaryotic – no nuclear membrane
Most cellular organelles are absent, except cell walls, plasma membranes, and ribosomes
Some may contain capsules and flagella and can develop endospores
Small – 0.2 to 2.0 mcg
Have requirements for temperature, pH, oxygen tension, and nutrition
Considered when collecting and preparing samples
Used to help identify samples
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4. Oxygen Requirements Obligate aerobes – require O2 to survive
Obligate anaerobes – growth inhibited or killed in the presence of O2
Facultative anaerobes – can survive in O2 but growth is limited
Microaerophilic – prefer reduced O2 tension
Capnophilic – require high levels of carbon dioxide
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5. Other Requirements pH – most live in the range of 6.5 to 7.5
Nutritional
Fastidious microbes – strict nutritional requirements
Agar medium
Temperature
Mesophiles – nearly all pathogenic bacteria in animals grow best at 20° to 40° C
Psychrophiles – lower temperatures
Thermophiles – higher temperatures
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6. Morphology Classified by shape and arrangement
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7. Morphology (cont.) Classified by arrangement
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8. Spores Some genera of bacteria have endospores
Resistant to heat, desiccation, chemicals, and radiation
Location in cell helps classify
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9. Bacterial Growth
Contain a single DNA strand and reproduce primarily by binary fusion
4 phases
Initial – lag phase – adapting to new media
Exponential – doubling or rapid growth
Continues until nutrients are used up, waste products accumulate, or space is limited
Stationary – no net increase or decrease
Final – death phase
Spore formation occurs during this phase
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10. Bacterial Growth (cont.)
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11. Fungal Characteristics
Heterotrophs
Parasitic or saprophytic (decomposers)
Most multicellular – except yeast
Eukaryotic cells with cell walls of chitin
Large webs (mycelium) of slender tubes (hyphae)
Grow toward food sources
Digest food internally – enzymes
Yeasts reproduce by budding
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12. Fungi Reproduction
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13. Pathogenic Fungal Organisms
Based on type of reproductive structures
Basidiomycetes – mushrooms or club fungi
Ascomycetes – cup fungi
Zygomycetes – molds
Deuteromycetes – fungi imperfecti
No known sexual stage occurs
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14. Virology Most testing done in specialized laboratories
Include histopathologic and serologic, electron microscopy, and attempted isolation of the virus
Many viral diseases are diagnosed on clinical and pathologic grounds
Serologic tests
Paired serum samples collected 2 to 3 weeks apart
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15. Virology (cont.) Isolation is expensive and time consuming Testing
May provide a diagnosis after death or recovery
In some instances, ID should be attempted
Not seen before
Public health issue
Epizootic
Testing
Collect aseptically, keep a 4° C, and take to laboratory ASAP
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16. Cell Culture Viruses need living cells to grow and replicate
Animals’ cells grown in vitro
Continuous cell lines and a single cell type
Fetal kidney, embryonic trachea, skin from laboratory animals
Inoculated into the primary culture from the same species from which the specimen was taken
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17. Immunologic and Molecular Diagnostics Examination
Clinical signs and cell culture may identify the virus to a family level and maybe genus and species level, but definitive ID requires serologic procedures
In-house tests are available for some viral pathogens
Molecular testing – PCR is also used to ID pathogens
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18. Summary
Bacterial morphologic characteristics are based on shape and arrangement of cells
Bacteria vary in requirements for oxygen, temperature, and nutrients
Some bacteria have specialized structures that can aid in identification
Different fungal groups produce different spores
Yeasts reproduce by budding – not spores
Fungi are classified by reproductive structures
Viral culture is performed in specialized laboratories
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