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Chapter 8*: SANITARY INSPECTION AND MICROBIOLOGICAL WATER QUALITY - page 18 / 52

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MPN Most probable number APHA American Public Health Association MUG 4-methylumbelliferyl-β-D-glucoside

1

2

ISO 9308-2 is at an early stage of revision by an ISO working group Not suitable for drinking water - lower limit of detection is 15 counts per 100 ml

Table 8.4 Standard methods for the determination of faecal streptococci (enterococci) - MPN methods

ISO 7899-1 (ISO, 1984a)1

APHA

2. Catalase

2. BHIB containing 6.5% NaCl Incubation conditions 24 h at 45°C Reaction Turbidity = (+)

Reaction Dark brown to black colonies surrounded by black halos

are (+) BEAA, with a (-) catalase test = faecal

A (+) PSE with a (+) BHIB (6.5% NaCl)

streptococci

= enterococcus group

ISO 7899-1 has been replaced recently with a new methodology proposed under the same ISO reference as in Table 8.7 1

MPN APHA BEAA PSE BHIB

Most probable number American Public Health Association Bile esculin azide agar Pfizer selective enterococcus Brain heart infusion broth

Isolation media Azide dextrose broth Incubation conditions

Brownish-black colonies with brown halos (+) for faecal streptococci

22 ± 2 h at 35 ± 1 °C or 37 ± 1 °C; negative tubes may be re-incubated for 22 ± 2 h

Reaction Turbidity = (+) Confirmatory media tests Two tests are recommended: 1. BEAA Incubation conditions 44 ± 4 h at 44 ± 0.5 °C

Azide dextrose broth Incubation conditions

24 ± 2 h at 35 ± 0.5 °C; negative tubes may be re-incubated until 48 ± 3 h

Reaction Turbidity = (+)

Two tests are recommended: 1. PSE agar Incubation conditions 24 ± 2 h at 35 ± 0.5 °C Reaction

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