The Examination of Foods for Enterobacteriaceae using a Test of the Type Generally Adopted for the Detection of Salmonellae

Abstract

S ummary : In countries that have recently increased their bacteriological inspection of foods, many products have shown considerable improvement in microbiological quality; simultaneously, however, discrepancies between salmonella and coli‐aerogenes tests, especially on dehydrated and frozen foods, have tended to become more frequent. These discrepancies have been eliminated by applying the following measures: incorporating glucose in culture media so as to reveal all Enterobacteriaceae; placing reliance on growth rather than gas formation so as to avoid missing anaerogenic organisms, and, especially, examining quantities of foods commensurate with those used in salmonella tests. For this purpose a procedure is recommended in which 10 g of well homogenized food are enriched in 100 ml of buffered brilliant green‐bile‐glucose broth, with no attention being paid to gas formation; the enrichment cultures are then streaked on to MacConkey's glucose agar. Single colonies so obtained are tested for fermentative attack on glucose and may be further examined for other characteristics. The same enrichment fluid can be used for the so‐called ‘nonselective pre‐enrichment’ of samples of food containing salmonellae impaired by periods spent in conditions of low water activity, low pH, etc.