Applied Microbiology: Food, Water, Soil, Industrial and Environmental
Introduction
This domain applies microbiology to food safety, water quality, soil fertility, industrial fermentation, and environmental management. The exam tests indicator organisms, preservation principles, and the difference between a microbial estimate and a health-risk conclusion.
Core rules
- Food spoilage and foodborne illness are controlled by temperature, water activity, pH, oxygen exclusion, preservatives, and HACCP-based process control.
- Drinking water is tested for coliforms and E. coli as indicators of faecal contamination; E. coli or thermotolerant coliforms should not be detectable in 100 mL of drinking water.
- MPN is a statistical estimate from a dilution series; membrane filtration gives a direct colony count for suitable volumes.
- Soil microorganisms drive nitrogen fixation, nitrification, decomposition, and bioremediation.
- Industrial microbiology uses controlled fermentation to produce antibiotics, enzymes, organic acids, and single-cell protein.
Worked example
A 100 mL drinking-water sample is filtered through a 0.45 µm membrane, incubated on a coliform-selective medium, and gives 30 typical colonies. Confirmatory tests identify 25 as coliforms. Report 250 coliforms per 100 mL. This exceeds the requirement of no detectable E. coli or thermotolerant coliforms in 100 mL, so the supply is not acceptable for drinking without treatment.
Traps
Coliforms are indicator organisms, not proof that every coliform is faecal. MPN is an estimate, not a direct count. A positive presumptive test needs confirmation. Not every industrial fermentation uses the same conditions; product yield depends on strain, medium, pH, temperature, and oxygen supply.