Further studies of incubation at 44° C. as a test for ‘faecal coli’

Abstract

1. The authors concluded in a previous paper that the most reliable single test for the detection ofBact. coliwas incubation in MacConkey's broth at 44° C, such a test forBact. colialone being necessary in shellfish because of occasional multiplication of other coliforms in purified mussels. The present investigation is an attempt to verify this finding on a broader basis.2. A description is given of the isolation of 1600 cultures of coliform organisms from polluted mussels, sewage, and faeces (human, cow, sheep and sea birds). Their classification according to ‘IMViC’ reactions and the production of gas in MacConkey's broth at temperatures of 37, 41, 44, 45 and 46° C. is given.3. Of the + + − − type, 1036 out of 1065 cultures (97·3%) were found to produce gas in MacConkey's broth at 44° C. A balance is noted between the + + − − type which does not produce gas at 44° C. (irregular I) and the two irregular types which do so (irregular II and irregular VI). Such a balance was reported by Bardsley (1938).4. From the cultures examined it is confirmed that incubation at 44° C. is the most suitable temperature for use with MacConkey's broth for permitting the maximum number ofBact. colito produce gas while inhibiting the maximum number of other coliforms.