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Chapter 8*: SANITARY INSPECTION AND MICROBIOLOGICAL WATER QUALITY - page 23 / 52

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Confirmatory media tests

Confirmatory media tests

Confirmatory media tests

In the case of the standard test, verify all or a representative number of typical colonies (at least 10), using the following series of tests:

Transfer the membrane filter to Tests are not required a bile esculin azide agar, preheated at 44°C; incubate at 44 ± 0.5 °C for 1 h

1. Non selective agar (i.e. tryptone soya agar); incubate for 21 ± 3 h at 36 ± 2°C4

The appearance of dark brown to black colonies surrounded by black halos = intestinal enterococci

2. Oxidase test; the non- appearance of a dark purple colour within 5-10 s indicates a negative result; a (-) oxidase = coliform bacteria

3. Tryptophane broth, incubate for 21 ± 3 h at 44 ± 0.5°C4

Add indol reagent; indol production (i.e. a red ring) indicates a positive result

A (-) oxidase and (+) indol = E. coli

For a rapid test, transfer the membrane filter to tryptone bile agar, incubate for 19-20 h at 44 ± 0.5°C4; place the membrane filter on a filter paper saturated with indol reagent; the appearance of red colonies = E. coli

MF

Membrane filtration

MPN Most probable number

TTC

Triphyl-tetrazolium chloride

MUD 4-methylumbelliferyl-β-D-glucoside

1

Suitable for drinking water with low background growth

2 Suitable for drinking water, swimming pools and other water with low intestinal enterococci

3 Not suitable for drinking water; lower limit of detection is 15 counts per 100 ml

These conditions substitute and standardise those from the previous ISO 9308-1 and 7899-2 4

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