The Value of the Association Escherichieae‐group D Streptococci in the Diagnosis of Contamination in Foods

SUMMARY: The tests for faecal contamination in foods, based on ‘indicator species’, should be reconsidered for the following reasons. First, in Europe, Escherichia coli is regarded as a specific index of such contamination; but, apparently through the use of antibiotics, the proportion of human faeces containing Klebsiella has risen from 5.2% in 1947 to 48.4% in 1956–7. Moreover, E. coli and other coli‐aerogenes organisms may be absent from the gut of certain animals, notably the pig. Second, while the usual methods of counting coli‐aerogenes bacteria do not permit the isolation of strains which ferment lactose slowly or not at all (i.e. paracolons), these occur in 35.6% of samples of human faeces. Further, the recommended methods of detecting such strains are not wholly satisfactory. Third, the origin of the coli‐aerogenes bacteria is uncertain. It is thus necessary to consider other organisms which normally inhabit the intestinal tract of humans and other animals. As to Clostridium perfringens , its source is doubtful, for it may come from faeces or from soil, and many foods contain only soil strains. The group D streptococci, on the other hand, are excellent indicators of faecal contamination. They are constant or frequent in the intestines of man and animals, and often more numerous there than coli‐aerogenes bacteria. Their specificity as an index of faecal contamination is high and their investigation is easy with the selective media now available. Associated with the coli‐aerogenes bacteria, they justify the diagnosis of faecal contamination in a foodstuff.