Transcript Microbiology

Microbiology
Unit 7
Chapter 37
Introduction to Microbiology
Copyright © 2015 by Mosby, an imprint of Elsevier Inc. All rights reserved.
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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Bacterial Cell Morphology
• Prokaryotic – no nuclear membrane
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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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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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Other Requirements
• pH – most live in the range of 6.5 to 7.5
• Nutritional
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Fastidious microbes – strict nutritional requirements
Agar medium
• Temperature
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Mesophiles – nearly all pathogenic bacteria in
animals grow best at 20° to 40° C
Psychrophiles – lower temperatures
Thermophiles – higher temperatures
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Morphology
• Classified by shape and arrangement
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Morphology (cont.)
• Classified by arrangement
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Spores
• Some genera of bacteria have
endospores
• Resistant to heat, desiccation, chemicals,
and radiation
• Location in cell helps classify
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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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Bacterial Growth (cont.)
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10
Fungal Characteristics
• Heterotrophs
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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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11
Fungi Reproduction
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12
Pathogenic Fungal Organisms
• Based on type of reproductive structures
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Basidiomycetes – mushrooms or club fungi
Ascomycetes – cup fungi
Zygomycetes – molds
Deuteromycetes – fungi imperfecti
• No known sexual stage occurs
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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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Virology (cont.)
• Isolation is expensive and time consuming
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May provide a diagnosis after death or recovery
In some instances, ID should be attempted
• Not seen before
• Public health issue
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Epizootic
• Testing
•
Collect aseptically, keep a 4° C, and take to
laboratory ASAP
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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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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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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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