Nutrient Agar w/Trypan blue is recommended by APHA for detection and enumeration of aerobic endospore formers from water samples by membrane filtration. The water samples under test is exposed to heat treatment wherein vegetative cells are destroyed and aerobic spores remain unaffected. The water sample is then filtered through membrane filter and placed on Agar plate. Incubate at 35±0.5°C for 24 ± 2 hours. Further incubation up to 5-7 days for intracellular formation of endospores. Trypan blue in the medium imparts a coloured background to the membrane. The aerobic endospores hence can be easily visualized and enumerated..
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