Overview
Total Viable Count (TVC) testing is used to assess the overall level of aerobic bacteria present in water systems. It is commonly carried out on final rinse water samples to help monitor hygiene, cleanliness, and microbiological quality.
All TVC testing is performed in accordance with UKAS accredited methods, ensuring reliable and recognised results.
Sample receipt and preparation
A 200 mL final rinse water sample is received by the laboratory and logged into the system upon arrival to ensure full traceability.
The sample is processed using a membrane filtration method to concentrate any microorganisms present.
The procedure involves:
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Placing a 0.45 micron nitrocellulose membrane filter onto a sterile filtration manifold
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Passing the measured water sample through the membrane
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Capturing bacteria on the surface of the filter
Following filtration, the membrane is aseptically transferred onto an agar plate for incubation.
Culture and incubation
Samples are cultured on R2A agar, the primary medium recommended in Health Technical Memorandum guidance for water testing.
R2A agar is a low-nutrient medium designed to:
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Support recovery of stressed or slow-growing bacteria
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Mimic the nutrient conditions found in water systems
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Promote the growth of a broad range of aerobic waterborne organisms
This makes it particularly suitable for routine monitoring of water quality.
Plates are incubated:
- At 30°C
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For 5 days
This extended incubation period allows visible colonies to develop, enabling accurate enumeration and assessment of microbial levels.
Results and reporting
After incubation, colonies are counted manually.
- Each visible colony represents one viable bacterium present in the original sample
- Results are calculated using duplicate plates to improve accuracy
- Final results are reported as colony forming units (CFU)
Results are reviewed in line with HTM guidance, and any results outside recommended limits can be highlighted and explained.
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