The effect of anaerobic spore-bearing organisms on the validity of the presumptive coliform test as used in the bacteriological examination of water: By the Public Health Laboratory Service Water Sub-Committee

The investigation of 10,436 fermented tubes arising in the presumptive coliform examination of samples of water at six laboratories in England and Wales has shown that, with unchlorinated supplies, the unconfirmed presumptive test gives sufficiently accurate results. Full confirmation of all presumptive positive tubes of these waters is impracticable as a routine and ‘colony-confirmation’ gives a correction of only 0·5%. With chlorinated waters, however, ‘colony-confirmation’ discloses an error of 5·5%, largely due to the presence of anaerobes. This error can also affect the faecal coli (44° C.) count and may be so large in individual samples that assessment of chlorinated supplies should not be based on the presumptive test until this has been checked at least by plating.