Microbiology Cheat Sheet
Food, Water, Milk & Air
Food, water, milk and air microbiology for NEET-PG: E. coli faecal indicator, MPN method, membrane filtration, MBRT, phosphatase test, and OT air standards.
MedNext Academy | 3 min read
Food, Water, Milk & Air
Food, water, milk and air microbiology for NEET-PG: E. coli faecal indicator, MPN method, membrane filtration, MBRT, phosphatase test, and OT air standards.
This topic covers the methods and significance of assessing microbial contamination of water, milk, and air in environmental and public health microbiology.
High-yield lines
- Indicator organisms are used to assess faecal contamination of water because direct detection of all waterborne pathogens is impractical.
- Total coliforms are lactose-fermenting Gram-negative bacilli at 37 degrees Celsius, indicating general environmental contamination.
- Escherichia coli, a thermotolerant coliform fermenting lactose at 44.5 degrees Celsius, is the most specific indicator of faecal contamination.
- The WHO drinking water standard is zero E. coli per 100 millilitres, a zero-tolerance criterion.
- The Multiple Tube Fermentation (MPN) method uses presumptive, confirmed, and completed tests, reporting results as most probable number per 100 millilitres.
- Membrane filtration passes a known water volume through a 0.45 micrometre membrane placed on selective medium, then counts colonies after incubation.
- The Standard Plate Count assesses milk quality, with Grade A pasteurised milk having fewer than 20,000 CFU per millilitre.
- The Methylene Blue Reduction Test indirectly measures milk bacterial load, with decolourisation time inversely proportional to bacterial count.
- The phosphatase test is the gold standard for pasteurisation quality control, as a positive result indicates inadequate pasteurisation.
- Milk-borne pathogens include Brucella, Mycobacterium bovis, Salmonella, Listeria monocytogenes, Campylobacter, and Coxiella burnetii.
- Air microbiology uses passive settle plates or active slit samplers, with the slit sampler being more accurate.
- Conventional operating theatre air standards permit up to 35 CFU per cubic metre, while ultraclean theatres with laminar airflow and HEPA filtration permit up to 10.
- Alkaline phosphatase is destroyed at pasteurisation temperatures, so its absence confirms adequate heat treatment.
- E. coli detection in water confirms faecal contamination, whereas total coliforms indicate only general environmental contamination.
Mapped competency codes
- MI8.8
Continue into the full chapter
This summary maps to MI8-zoonotic-diseases-and-miscellaneous.
Frequently Asked Questions
What is the WHO standard for E. coli in drinking water?
Zero E. coli per 100 millilitres, a zero-tolerance faecal contamination criterion.
Which test confirms adequate milk pasteurisation?
The phosphatase test, since alkaline phosphatase is destroyed at pasteurisation temperatures and a positive result indicates inadequate heating.
What are the two standard bacteriological methods for water testing?
The Multiple Tube Fermentation (MPN) method and membrane filtration.
Why is E. coli the best indicator of faecal contamination in water?
It is a thermotolerant coliform that ferments lactose at 44.5 degrees Celsius and is specific to faecal origin, unlike general environmental coliforms.
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