Bacteriolgy

What is the importance of proper specimen collection in clinical bacteriology?

To avoid contamination, ensure accurate diagnosis, and improve pathogen recovery.

Give an example of a sterile site for specimen collection.

Blood, cerebrospinal fluid (CSF), pleural fluid.

How should cerebrospinal fluid (CSF) be transported to the lab?

Immediately at body temperature (37°C) to prevent bacterial death.

What is the purpose of selective media?

To inhibit unwanted bacteria and allow growth of the target pathogen (e.g., MacConkey agar for Gram-negative bacteria).

What is the function of Blood Agar?

Enriched & differential – Detects hemolysis patterns (α, β, γ).

What medium is used for Vibrio cholerae?

TCBS agar (Thiosulfate Citrate Bile Salts Sucrose) – Yellow colonies indicate sucrose fermentation.

What color do Gram-positive and Gram-negative bacteria appear on a Gram stain?

Gram-positive: Purple; Gram-negative: Pink.

What is the oxidase test used for?

Differentiates oxidase-positive bacteria (e.g., Pseudomonas, Vibrio) from oxidase-negative ones (e.g., Enterobacteriaceae).

Which bacteria are coagulase-positive?

Staphylococcus aureus (used to differentiate from Staphylococcus epidermidis).

What are the two main methods of Antibiotic Susceptibility Testing (AST)?

Disk Diffusion (Kirby-Bauer Test) – Measures zone of inhibition; Minimum Inhibitory Concentration (MIC) – Determines the lowest concentration that inhibits bacterial growth.

Which test detects MRSA?

Cefoxitin disk diffusion test or PCR for the mecA gene.

What does an ESBL-producing bacterium indicate?

Extended-spectrum beta-lactamase (ESBL) production = resistance to 3rd gen cephalosporins (e.g., E. coli, Klebsiella).

Which bacterium causes "rice-water stools"?

Vibrio cholerae.

What is the primary pathogen in cystic fibrosis lung infections?

Pseudomonas aeruginosa (forms biofilms).

What are the most common non-glucose fermenting Gram-negative bacilli?

Pseudomonas aeruginosa, Acinetobacter baumannii, Burkholderia cepacia.

Name two hospital-acquired infections caused by Acinetobacter baumannii.

Ventilator-associated pneumonia (VAP) and bloodstream infections.

Name two strategies to prevent hospital-acquired bacterial infections.

Hand hygiene & disinfection; Antibiotic stewardship programs.

How can hospitals reduce Clostridioides difficile infections?

Use of soap and water instead of alcohol-based sanitizers; Judicious antibiotic use (avoiding broad-spectrum antibiotics).

What is the role of antimicrobial stewardship programs?

To promote rational antibiotic use, reduce resistance, and improve patient outcomes.