Bacterial Basics
What are the three major bacterial shapes?
Cocci, bacilli, and spirilla.
Which biosafety level (BSL) is used in most veterinary diagnostic bacteriology labs?
BSL-2
Which antibiotic class inhibits bacterial cell wall synthesis?
Beta-lactams.
What is the most important principle when collecting a sample for bacteriology?
Avoid contamination.
What is the first step in bacterial infection?
Adhesion to host cells.
Gram-negative bacteria stain pink because of what structural feature?
A: Thin peptidoglycan and an outer membrane with lipopolysaccharide (LPS).
Define sterilization.
Complete destruction of all microbial life, including spores.
Aminoglycosides inhibit bacterial protein synthesis at which ribosomal subunit?
30S.
What type of swab is preferred for bacterial transport?
Sterile swab with transport medium (e.g., Amies).
Exotoxins differ from endotoxins in what key way?
Exotoxins = secreted proteins; endotoxins = lipid A of Gram− LPS.
A culture of Escherichia coli reveals motility. Which structure enables this?
Flagella
A disinfectant is applied to a stall surface, while an antiseptic is applied to a wound. What is the key difference between these processes?
Disinfection = inanimate objects; antisepsis = living tissue.
A dog is treated with a bacteriostatic antibiotic. What does this mean about its action?
It halts bacterial growth but doesn’t directly kill bacteria.
A fecal sample suspected for Clostridium must be transported. What special consideration is required?
Use anaerobic transport media to protect from oxygen.
Which bacterial component triggers septic shock in veterinary patients?
Endotoxin (LPS).
A calf with pneumonia is infected with a bacterium carrying multiple resistance genes. Which bacterial structure most likely mediates this resistance transfer?
Plasmids
A necropsy technician needs to inactivate Bacillus anthracis spores. Which chemical is most effective?
Chlorine compounds (e.g., bleach at proper concentration).
Which class of antibiotics should be dosed less frequently but at higher doses due to concentration-dependent killing?
Aminoglycosides.
Why are selective media critical in culturing veterinary samples such as feces?
They suppress normal flora while allowing pathogens to grow.
How do bacteria evade host immunity through antigenic variation?
They alter surface proteins, escaping immune recognition.
Which bacterial structure both enhances virulence and complicates vaccine development by preventing what?
Capsules.phagocytosis
Which part of the “chain of infection” is targeted by quarantine and movement restrictions, and why?
Host–environment interaction, by limiting transmission opportunities.
A horse with septic arthritis is placed on antibiotics. The veterinarian selects a drug with “four-quadrant coverage.” What does this term mean?
Covers Gram+, Gram−, aerobic, and anaerobic organisms.
A wound suspected to contain Clostridium perfringens is refrigerated before culture. What is the likely outcome?
Anaerobes will die due to increased oxygen solubility in cold storage.
What is quorum sensing, and why does it matter in pathogenesis?
Bacterial communication via signaling molecules that coordinate virulence gene expression.