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Chapter 8*: SANITARY INSPECTION AND MICROBIOLOGICAL WATER QUALITY - page 17 / 52

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Table 8.3 Standard methods for the determination of thermotolerant coliforms (E. coli presumptive) - MPN methods

ISO 9308-2 (ISO, 1990c)1

ISO 9308-3 (96 wells)2 (ISO, 1998)

APHA

Isolation media

  • a)

    Lactose broth

  • b)

    MacConkey broth

  • c)

    Lauryl tryptose (lactose) broth

  • d)

    Formate lactose glutamate medium

Incubation conditions 24-48 h at 35 ± 1 °C or 37 ± 1 °C

Reaction Turbidity = (+)

Confirmatory media tests Two confirmatory methods can be used:

A. With two steps 1.

  • a)

    EC medium

  • b)

    Brilliant green lactose (bile) broth

Incubation conditions 24 h at 44 ± 0.25°C or 44.5 ± 0.25°C Reaction Gas production = (+) for thermotolerant coliforms

2. Tryptone water

Incubation conditions 24 h at 44 ± 0.25°C or 44.5 ± 0.25°C Reaction

Indol production with indol reagent Kovacs = (+) for E. coli

B. With one step Lauryl tryptose mannitol broth with tryptophan Incubation conditions 24 h at 44 ± 0.25 °C or 44.5 ± 0.25 °C Reactions

Gas production = (+) and indol = (+/-) for thermotolerant coliforms; gas production = (+) and indol = (+) for E. coli

Tryptone salicine triton MUG broth (MU/EC)

  • a)

    EC medium, or

  • b)

    A-1 medium

Incubation conditions 36-72 h at 44 ± 0.5 °C

Incubation conditions

  • a)

    24 ± 2 h at 44.5 ± 0.2 °C

  • b)

    3 h at 35 ± 0.5 °C followed

by 21 ± 2 hat 44.5 ± 0.2 °C

Reaction Reaction

Blue fluorescence = (+) for E. coli

a) and b) Gas production = (+) for thermotolerant coliforms

Confirmatory tests are not required

If using EC medium, verify with the following test:

Brilliant green lactose (bile) broth

Incubation conditions 24 ± 2 h at 44.5 ± 0.2 °C Reaction

Gas production = (+) for thermotolerant coliforms

If using A-1 medium, a confirmatory test is not required

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