Transcription of Annex 5 Multiple-tube method for thermotolerant …
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Annex 5 Multiple-tube method for thermotolerant …
Annex 5189 Annex 5 Multiple-tube method forthermotolerant (faecal) coliformsIn the Multiple-tube method , a series of tubes containing a suitable selective brothculture medium is inoculated with test portions of a water sample. After aspecified incubation time at a given temperature, each tube showing gas forma-tion is regarded as presumptive positive since the gas indicates the possiblepresence of coliforms. However, gas may also be produced by other organisms,and so a subsequent confirmatory test is essential. The two tests are knownrespectively as the presumptive test and the confirmatory the confirmatory test, a more selective culture medium is inoculated withmaterial taken from the positive tubes . After an appropriate incubation time, thetubes are examined for gas formation as before. The most probable number (MPN)of bacteria present can then be estimated from the number of tubes inoculatedand the number of positive tubes obtained in the confirmatory test, using spe-cially devised statistical tables.
GUIDELINES FOR DRINKING-WATER QUALITY 194 alternatives include a 0.1% solution of peptone in distilled water (final pH 6.8),
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