Medical Microbiology (Bacteriology, Virology, Mycology)
Domain focus
Medical microbiology tests bacteriology, virology and mycology: specimen selection, Gram stain, culture, identification, antimicrobial susceptibility testing, and interpretation of TB, HIV viral load and fungal investigations relevant to Cambodia.
Core rules
- Collect specimens before antibiotics whenever possible and transport in the correct medium and temperature.
- A Gram stain is a rapid guide, not a final identification; correlate with culture.
- Use standardised AST methods (disk diffusion or MIC) and current interpretive tables; report only tested and relevant agents.
- For sputum AFB, use concentrated smears and culture or molecular testing; a negative smear does not exclude TB.
- Interpret viral load trends, not single values, and use plasma EDTA for HIV RNA testing.
Worked example
A CSF sample from a febrile child shows many neutrophils and Gram-negative diplococci. The report should state 'Gram-negative diplococci seen - suggestive of Neisseria meningitidis; culture pending'. The reasoning is that morphology plus CSF pleocytosis supports presumptive meningococcal meningitis, but identity and susceptibility require culture or PCR. Clinicians need the provisional result immediately.
Traps
- Calling a contaminated sputum culture a pathogen without assessing squamous epithelial cells.
- Reporting an ESBL or carbapenemase phenotype without confirmatory testing.
- Using a urine colony count alone to diagnose infection in a catheterised patient.
- Ignoring the window between antibiotic dose and culture collection.