Microbiology and Applied Microbiology
Microbiology and Applied Microbiology tests cultivation, control, enumeration, and identification of microorganisms, plus their industrial and environmental uses.
Core rules
- Media may be selective, differential, or both. Sterilization kills all viable organisms; disinfection reduces pathogens on surfaces; sanitization lowers counts to a public-health standard.
- Bacterial growth in batch culture passes through lag, log, stationary, and death phases. Stationary phase reflects nutrient limitation and waste accumulation.
- A viable count assumes each colony arises from one colony-forming unit; counts are reliable in the 30-300 colony range.
- Gram staining distinguishes thick peptidoglycan Gram-positive cells from thin-peptidoglycan, outer-membrane Gram-negative cells; it is not a taxonomic proof.
- Industrial microbiology uses pure cultures, inoculum development, containment, and downstream processing.
Worked example
A 0.1 mL sample of a 10^-5 dilution is spread on an agar plate, and 120 colonies develop. CFU/mL = colonies / (dilution x volume plated) = 120 / (10^-5 x 0.1) = 1.2 x 10^8 CFU/mL. The result is a viable count, not a total cell count. If the plate had 350 colonies, the count would be outside the reliable range and the dilution should be repeated.
Traps
Do not report CFU as exact cells; clumps and chains count as one unit. Do not autoclave heat-labile media or antibiotics. Do not confuse selective with differential media. Do not use a single plate count outside 30-300 without justification. Do not assume a clear zone always means susceptibility in a disc test without standard conditions.