Microbiology Unit 7 Chapter 37 Introduction to Microbiology

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 Copyright © 2015 by Mosby, an imprint of Elsevier Inc. All rights reserved. 2

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, p. H, oxygen tension, and nutrition • • Considered when collecting and preparing samples Used to help identify samples Copyright © 2015 by Mosby, an imprint of Elsevier Inc. All rights reserved. 3

Oxygen Requirements • Obligate aerobes – require O 2 to survive • Obligate anaerobes – growth inhibited or killed in the presence of O 2 • Facultative anaerobes – can survive in O 2 but growth is limited • Microaerophilic – prefer reduced O 2 tension • Capnophilic – require high levels of carbon dioxide Copyright © 2015 by Mosby, an imprint of Elsevier Inc. All rights reserved. 4

Other Requirements • p. H – 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 Copyright © 2015 by Mosby, an imprint of Elsevier Inc. All rights reserved. 5

Morphology • Classified by shape and arrangement Copyright © 2015 by Mosby, an imprint

Morphology (cont. ) • Classified by arrangement Copyright © 2015 by Mosby, an imprint

Spores • Some genera of bacteria have endospores • Resistant to heat, desiccation, chemicals, and radiation • Location in cell helps classify Copyright © 2015 by Mosby, an imprint of Elsevier Inc. All rights reserved. 8

Bacterial Growth • Contain a single DNA strand 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 Copyright © 2015 by Mosby, an imprint of Elsevier Inc. All rights reserved. 9

Bacterial Growth (cont. ) Copyright © 2015 by Mosby, an imprint of Elsevier Inc.

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 Copyright © 2015 by Mosby, an imprint of Elsevier Inc. All rights reserved. 11

Fungi Reproduction Copyright © 2015 by Mosby, an imprint of Elsevier Inc. All rights

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 Copyright © 2015 by Mosby, an imprint of Elsevier Inc. All rights reserved. 13

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 Copyright © 2015 by Mosby, an imprint of Elsevier Inc. All rights reserved. 14

Virology (cont. ) • Isolation is expensive and time consuming • • 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 Copyright © 2015 by Mosby, an imprint of Elsevier Inc. All rights reserved. 15

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 Copyright © 2015 by Mosby, an imprint of Elsevier Inc. All rights reserved. 16

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 Copyright © 2015 by Mosby, an imprint of Elsevier Inc. All rights reserved. 17

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 Copyright © 2015 by Mosby, an imprint of Elsevier Inc. All rights reserved. 18