SUMMARYWe report a study to determine the presence of Listeria species in surface waters. One hundred ml volumes of 30 water samples taken from 21 different sites were analysed. Most of the samples examined were from ponds and lakes. Listeria species were isolated on eight (27%) occasions, six of these isolates were L. seeligeri, one was L. innocua and one L. welshimeri. Although not statistically significant, coliform and Escherichia coli counts were higher in waters that were positive than were negative for Listeria spp. It is suggested that the low isolation rate of listeria in this study reflects the fact that most waters examined did not receive sewage outfalls. Water sports activities are unlikely to be a risk factor for listeriosis.
A survey of the bacteriological quality of pre‐packed sandwiches on sale in the UK is reported. A total of 91 sandwiches, of which 46 had been on display at ambient temperature, were analysed. Total viable counts were high: 38 per cent of all sandwiches had counts greater than 10⊃7. Coliforms were isolated from 37 per cent of the samples and at levels greater than 10⊃7 in 10 per cent. Listeria monocytogenes was isolated from 17 per cent of all sandwiches. Sandwiches that had been on display at ambient temperature had higher total viable counts and were more likely to contain listeria (28 per cent compared to 7 per cent for those stored at chilled temperatures). A small follow‐up study of sandwich ingredients found high counts in salad. The significance to the public health of the high contamination rate by listeria is unclear. Nevertheless, it would seem appropriate to ensure that sandwiches are always adequately refrigerated.
A survey of the microbiological quality of tripe purchased in the Cheshire area was undertaken. Forty‐four samples were analysed during a 4 month period in 1991. Total viable counts were frequently high for a cooked product, 40% being 106 or greater. Listeria monocytogenes was isolated by enrichment from 9% of samples. Aeromonas spp. were isolated from 48% of samples. All 11 Aeromonas isolates, sent for further identification, were A. hydrophila. In some instances the count of Aeromonas was very high, being greater than 107 in two samples.
Reports on a study of the bacteriological and mycological quality of 87 prepared salads purchased from delicatessens. Bacterial counts were generally low. Of the 87 salads, only 19 per cent had plate counts greater than 104 organisms/g. Coliforms were isolated from three samples, E. coli from one and Listeria monocytogenes from one. By contrast yeasts were isolated from 76 per cent of the salads and at counts greater than 104 organisms/g in 31 per cent. Twenty‐one different yeast species were isolated, of which the commonest were Saccharomyces dairensis and Saccharomyces exiguus. Few of the yeasts have any significant role in human disease. The commonest yeasts isolated, however, are associated with spoilage of mayonnaise‐based salads. Their isolation from these foods suggests inadequate temperature control.
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