Veterinary Biology – Microbiology Final Exam Study Guide

These flashcards cover key vocabulary terms and definitions from the Veterinary Biology - Microbiology final exam study guide.

Sanitation

Reduces microbial load in kennels, stalls, and clinical areas.

Sterilization

Eliminates all microorganisms; used for surgical tools.

Disinfection

Removes most pathogens on surfaces, not spores.

Antiseptics

Safe for animal skin, examples include iodine and chlorhexidine.

Biofilms

Cause chronic infections and resist antibiotics, commonly found in ears, teeth, and catheters.

Gram-positive bacteria

Have thick peptidoglycan layers; common in skin infections.

Gram-negative bacteria

Characterized by an outer membrane containing LPS; more drug-resistant.

LPS (endotoxin)

Causes fever, inflammation, and shock in animals.

Anaerobes

Bacteria that grow without oxygen; common in abscesses.

Facultative anaerobes

Bacteria that can grow with or without oxygen.

Mycoplasma

Bacteria that lack cell walls and resist penicillin.

Spirochetes

A type of bacteria, like Leptospira, that are zoonotic.

Viruses

Obligate intracellular parasites that require a host to replicate.

Enveloped viruses

Viruses that are fragile; non-enveloped viruses are very stable.

Rabies

A fatal zoonotic RNA virus.

Prions

Infectious agents that cause fatal neurologic diseases, such as mad cow disease.

Fungi

Eukaryotic organisms with chitin cell walls.

Ringworm

A contagious zoonotic fungal infection.

Yeasts

Common in causing ear infections in dogs.

Opportunistic fungi

Infect immunocompromised animals.

Virulence factors

Attributes of pathogens that increase disease severity.

Zoonoses

Diseases that transmit from animals to humans.

Innate immunity

Nonspecific immune response.

Adaptive immunity

Specific immune response that develops over time.

Vaccines

Medical preparations that create immune memory.

Antibiotics

Drugs that target bacterial structures and metabolism.

Resistance

Arises from the misuse and overuse of antibiotics.

Aseptic technique

Methods used to prevent contamination in laboratory settings.

Culture and sensitivity testing

Laboratory tests that guide treatment by identifying pathogens and their sensitivities.

Kirby-Bauer test

A method that measures antibiotic susceptibility.

Module 2: Sanitation vs. Disinfection

1. Sanitation: Reducing microbial populations to levels considered safe by public health standards (99.9\% reduction).

2. Disinfection: Destruction of most pathogenic organisms on inanimate objects; does not typically eliminate bacterial spores.

Module 2: Sterilization Standards (Autoclaving)

The standard protocol for sterilization using pressurized steam is 121^{\circ}C (250^{\circ}F) at 15 psi for at least 15 minutes. This process effectively kills all microorganisms, including highly resistant endospores.

Module 2: Biofilm Formation Stages

1. Reversible Attachment: Bacteria adhere to a surface using pili or fimbriae.

2. Irreversible Attachment: Microbes produce an extracellular polymeric substance (EPS).

3. Maturation: The biofilm thickens and develops complex architectures.

4. Dispersion: Planktonic cells are released to colonize new sites.

Module 2: Factors affecting Germicidal Activity

1. Contact Time: Longer exposure increases efficacy.

2. Temperature: Higher temperatures usually enhance chemical activity.

3. Organic Matter: Blood, feces, or soil can neutralize disinfectants.

4. Concentration: Over-dilution reduces effectiveness; however, some agents (like 70\% alcohol) require water to work.

Module 2: Quaternary Ammonium Compounds (Quats)

Cationic detergents used as disinfectants that disrupt the cell membrane. They are effective against Gram-positive bacteria and enveloped viruses but ineffective against spores and many Gram-negative bacteria like Pseudomonas.

Module 3: Peptidoglycan Structure

A mesh-like polymer consisting of sugars (NAG and NAM) cross-linked by short peptides.

• Gram-positive: Contains many layers (20-80 nm).

• Gram-negative: Contains a single, thin layer (2-7 nm).

Module 3: Gram Stain Reagents and Order

1. Primary Stain: Crystal Violet (stains all cells purple).

2. Mordant: Iodine (forms CV-I complex).

3. Decolorizer: Alcohol or Acetone (extracts lipids from Gram-negative walls).

4. Counterstain: Safranin (stains decolorized Gram-negative cells pink/red).

Module 3: Lipopolysaccharide (LPS) Components

Found in the outer membrane of Gram-negative bacteria, consisting of:

1. Lipid A: The toxic moiety (endotoxin).

2. Core Polysaccharide: Provides structural stability.

3. O-Antigen: Extends outward; used for strain identification (serotyping).

Module 3: Porins and Drug Resistance

Channel-forming proteins in the outer membrane of Gram-negative bacteria. Mutations in porins can exclude certain antibiotics (like Beta-lactams), preventing them from reaching their targets in the periplasm.

Module 3: Teichoic and Lipoteichoic Acids

Anchored in the Gram-positive cell wall. They provide negative charge to the cell surface, assist in binding cations, and play roles in cell wall maintenance and attachment to host tissues.

Module 4: Obligate vs. Facultative Anaerobes

• Obligate Anaerobes: Lack enzymes like Superoxide Dismutase (SOD) or Catalase; oxygen is toxic to them (e.g., Clostridium).
• Facultative Anaerobes: Can utilize oxygen for aerobic respiration but switch to fermentation/anaerobic respiration when oxygen is absent (e.g., Escherichia coli).

Module 4: Mycoplasma Characteristics

Bacteria that naturally lack a cell wall.

• They contain sterols in their plasma membrane for stability.
• They are pleomorphic (variable shape).
• Inherently resistant to antibiotics targeting cell wall synthesis (e.g., Penicillins).

Module 4: Spirochetes Morphology and Movement

Long, slender, spiral-shaped bacteria that use endoflagella (axial filaments) located in the periplasmic space. This allow them to move in a corkscrew fashion through viscous fluids (e.g., Leptospira, Borrelia).

Module 4: Obligate Intracellular Bacteria

Bacteria that must live inside a host cell to replicate, as they rely on the host for ATP or other metabolites. Examples include Chlamydia and Rickettsia.

Module 4: Endospore-Forming Bacteria

Primarily Bacillus and Clostridium species. They produce highly resistant dormant structures (spores) in response to environmental stress, allowing survival for decades.

Module 5: Viral Structure (Capsid and Envelope)

• Capsid: Protein shell surrounding the viral genome (DNA or RNA).

• Envelope: Lipid bilayer derived from the host cell membrane; contains viral glycoproteins (spikes) used for attachment.

Module 5: Viral Replication Cycle

1. Attachment: Binding to specific host receptors.

2. Entry/Penetration: Endocytosis or membrane fusion.

3. Uncoating: Release of genome from capsid.

4. Biosynthesis: Replication of genome and protein synthesis.

5. Assembly: Packaging of new virions.

6. Release: Budding (enveloped) or Lysis (non-enveloped).

Module 5: Retroviruses and Reverse Transcriptase

RNA viruses (e.g., FeLV, FIV) that carry the enzyme Reverse Transcriptase. This converts their RNA genome into DNA, which is then integrated into the host's genome as a provirus.

Module 5: Prion Pathogenesis (PrPSc)

Prions occur when normal cellular protein (PrP^{C}) is converted into an abnormal, protease-resistant isoform (PrP^{Sc}). This promotes a chain reaction of misfolding, leading to amyloid plaques and spongiform changes in the brain.

Module 5: Bacteriophages

Viruses that infect bacteria specifically.

• Lytic Cycle: Directs cell to produce new phages and eventually lyses (kills) the host.

• Lysogenic Cycle: Integrates into the bacterial chromosome as a prophage, replicating along with the host.

Module 6: Ergosterol in Fungi

The primary sterol in fungal cell membranes (analogous to cholesterol in animals). It is the major target for many antifungal drugs, such as Amphotericin B and Azoles.

Module 6: Dimorphic Fungi

Fungi that can exist in two forms depending on environmental conditions (usually temperature):

• Yeast form at body temperature (37^{\circ}C).

• Mold (hyphal) form at environmental temperatures (25^{\circ}C).

Module 6: Hyphae Types

• Septate: Hyphae with cross-walls (septa) dividing cells.

• Aseptate (Coenocytic): Hyphae lacking cross-walls, appearing as long continuous cells with multiple nuclei.

Module 6: Dermatophytosis (Ringworm)

A superficial fungal infection of keratinized tissues (skin, hair, nails). Caused by Microsporum or Trichophyton. It is highly zoonotic and spreads via arthrospores.

Module 6: Mycotoxicosis

Diseases caused by the ingestion of toxic secondary metabolites (mycotoxins) produced by fungi, such as Aflatoxin produced by Aspergillus species often found in moldy feed.

Module 7: Microbial Adhesins

Surface molecules (lectins, fimbriae, capsules) that allow pathogens to bind to specific host cell receptors. This is the critical first step in establishing an infection.

Module 7: Exotoxins vs. Endotoxins

• Exotoxins: Proteins secreted by living cells (usually Gram-positive); highly potent and target specific organs (e.g., Tetanus toxin).

• Endotoxins: LPS released from dead Gram-negative bacteria; cause systemic effects like fever and shock.

Module 7: Phagocytosis Steps

1. Chemotaxis: Movement toward the microbe.

2. Adherence: Attachment of the phagocyte (e.g., Neutrophil) to the microbe.

3. Ingestion: Formation of a phagosome.

4. Digestion: Fusion with lysosome to form a phagolysosome.

5. Exocytosis: Elimination of waste.

Module 7: Antibody Isotypes in Animals

1. IgG: Most abundant in serum; provides long-term immunity.

2. IgM: First antibody produced in a primary response.

3. IgA: Found in mucosal secretions (milk, tears, saliva).

4. IgE: Involved in allergic reactions and parasite defense.

Module 7: MHC Molecules

• MHC I: Found on all nucleated cells; presents endogenous antigens to CD8+ T cells (cytotoxic).

• MHC II: Found on specialized Antigen-Presenting Cells (APCs); presents exogenous antigens to CD4+ T cells (helper).

Module 8: Mechanism of Action: Beta-Lactams

Antibiotics (e.g., Penicillin, Cephalosporins) that inhibit Transpeptidase enzymes responsible for cross-linking peptidoglycan chains. This results in a weakened cell wall and osmotic lysis of the bacterium.

Module 8: Bacteriostatic vs. Bactericidal

• Bacteriostatic: Inhibits bacterial growth and reproduction (e.g., Tetracyclines) allowing the immune system to clear the infection.

• Bactericidal: Directly kills the bacteria (e.g., Aminoglycosides, Fluoroquinolones).

Module 8: Antibiotic Resistance Mechanisms

1. Target Modification: Changing the binding site (e.g., MRSA).

2. Enzymatic Inactivation: Breaking the drug down (e.g., Beta-lactamases).

3. Efflux Pumps: Pumping the drug out of the cell.

4. Reduced Permeability: Closing porins to block drug entry.

Module 8: Horizontal Gene Transfer (HGT)

Methods by which bacteria share resistance genes:

1. Conjugation: Transfer via sex pilus (Plasmids).

2. Transformation: Uptake of DNA from the environment.

3. Transduction: Transfer via bacteriophages.

Module 8: Therapeutic Index (TI)

The ratio of the dose that is toxic to the host to the dose that is effective against the pathogen. A high TI suggests the drug is safer for the animal.

Module 9: Differential vs. Selective Media

• Selective: Contains inhibitors that allow only certain microbes to grow (e.g., MacConkey agar inhibits Gram-positives).

• Differential: Contains indicators that reveal metabolic differences (e.g., Blood agar shows hemolysis patterns).

Module 9: Catalase and Coagulase Tests

• Catalase: Differentiates Staphylococcus (+) from Streptococcus (-).

• Coagulase: Differentiates pathogenic Staph. aureus (+) from less virulent Coagulase-negative staphylococci.

Module 9: Hemolysis Patterns on Blood Agar

1. Alpha (\alpha): Partial clearing/greenish discoloration.

2. Beta (\beta): Complete clearing (lysis) of red blood cells.

3. Gamma (\gamma): No hemolysis (no change in media).

Module 9: Kirby-Bauer Method (Disc Diffusion)

A standardized test where antibiotic discs are placed on a Mueller-Hinton agar plate inoculated with a bacterial lawn. The Zone of Inhibition is measured (mm) and compared to a chart to determine 'Susceptible', 'Intermediate', or 'Resistant'.

Module 9: PCR (Polymerase Chain Reaction)

A molecular technique used to amplify specific segments of DNA. It consists of three steps: Denaturation, **Anne