The source of Yersinia spp. in pasteurized milk: an investigation at a dairy.

Pasteurized bottled milk supplied by a single dairy was frequently found to be contaminated with Yersinia spp. Investigations were carried out at the dairy in an effort to pinpoint the source of these organisms. Viable counts obtained from milk bottle rinses indicated that bottle washing was often unsatisfactory, and on one occasion Y. frederiksenii was isolated from the pooled rinse water of six bottles. Samples of milk were taken on arrival at the dairy and at various stages following pasteurization. Heat resistance tests carried out on strains of yersinia isolated from pasteurized milk indicated that they would not survive the pasteurization process. However two strains of yersinia were isolated from a sample of milk taken immediately after pasteurization but before bottling. The thermograph indicated that the time/temperature conditions applied during pasteurization were adequate. The presence of yersinia strains in the milk at this stage therefore suggests that undetectable levels of raw milk were being allowed to contaminate the pasteurized milk. The absence of yersinia in cartoned samples produced on the same day as contaminated bottled samples indicated that environmental contamination of the bottle filler valve also may have occurred at times. Results of this investigation indicate that increased vigilance is required to ensure proper operation of pasteurizers and bottle washers.

Excretion of Yersinia spp. associated with consumption of pasteurized milk.

Yersinia enterocolitica biotype 1, serotype O.10K was isolated from 19 patients in the paediatric wards of a district general hospital over a period of 3 months. Fifteen cases were patients on the medical ward. Shortly afterwards, Y. enterocolitica biotype 1, serotype O.6, 30 was isolated from a further 17 patients on this ward in 1 month. The same serotypes of Y. enterocolitica were isolated from the pasteurized milk supplied to the ward. Epidemiological evidence indicated that contaminated pasteurized milk was the source of the yersinia organisms excreted by the patients.

The use of alkalinity and incubation at 9 degrees C for improved recovery of Yersinia spp. from faeces.

Recovery of Yersinia enterocolitica and related strains from faecal samples enriched in 1% buffered peptone water (pH 7.2) and incubated at 4 degrees C for 7-21 days was compared with recovery from 1% peptone water buffered to pH 8.0 and incubated over the temperature range 4-26 degrees C. Best recovery was obtained by use of the alkaline medium incubated at 9 degrees C. Greatest recovery was obtained after incubation for 10-14 days, but most strains (greater than 75%) were recovered after 1 week.

An appraisal of methods used in the examination of retail samples of cows milk.

The use of the methylene blue test for the examination of cows milk was investigated in an inter-laboratory survey. A poor relationship was found between results of these tests and total viable counts. Coliforms were detected in a large number of pasteurized milks, indicating frequent post-pasteurization contamination. No relationship was found between the results of the methylene blue test and the presence of coliforms. Results from this survey highlight the need for reappraisal of the methylene blue test as a statutory method for the examination of milk. A total viable count and coliform test are suggested for providing information regarding dairy hygiene and the quality of the product at the point of retail sale.

Human carriage of Yersinia spp.

Examination of faecal specimens for the presence of Yersinia spp. during a 1-year period yielded isolations from 3.5% of patients. Salmonella spp., Campylobacter spp. and Shigella spp. were isolated from 2.5%, 2.8% and 0.34% of patients respectively. Most isolates belonged to Y. enterocolitica biotype 1 (53%) and Y. frederikseni (39%). The most frequently encountered serotypable strains were serotypes O 5.27 and O 6.30. Serotype O 3, the commonly recognised pathogenic strain, was not isolated in this survey. A strong association between Yersinia excretion and the age group 1-14 years was demonstrated. Although biotype-1 strains and Y. frederikseni have not previously been thought to be pathogenic, clinical significance could be attributed to the presence of Yersinia spp. in almost 90% of patients aged 15 years or more, and in over 50% of patients in the younger age groups.

A rare case of meningitis due to Neisseria meningitidis group 29E.

We report a case of meningitis due to Neisseria meningitidis group 29E. The organism was serum-sensitive and therefore not expected to be encountered in an immunologically competent young man. Trauma sustained in a road traffic accident 18 months earlier had affected the tympanic membrane and middle ear, allowing direct infection of the meninges. Myringoplasty was performed to prevent recurrent infection.

The microbiology of cooked prawns and shrimps on retail sale.

In an inter-laboratory survey, 148 samples of cooked prawns and shrimps were obtained at the point of sale to the consumer. Salmonellae and Vibrio parahaemolyticus were not detected. Yersinia enterocolitica was isolated from three samples. Results for total viable count and presence of Escherichia coli and Staphylococcus aureus complied well with available guidelines for imported cooked prawns, suggesting that the risk of food poisoning from retail samples of these foods in the South of England is minimal.

The microbiology of selected retail food products with an evaluation of viable counting methods.

In an inter-laboratory survey, the pour plate, surface spread, agar droplet and spiral plate methods were used in parallel with the surface drop method for enumeration of micro-organisms in foods. Good agreement was obtained between all surface methods of enumeration, but there was poor agreement between molten agar methods and the surface drop method. A total of 1143 samples of food that were ready for consumption at the point of retail sale were examined. Eight types of food products were chosen: meat pasties, sausage rolls, real-cream slices, synthetic-cream slices, mayonnaise-based coleslaws, faggots, patés and continental sausages. The results of this survey suggest that the upper limit for an acceptable viable count should vary according to the food product. Salmonellae were not isolated on any occasion. Potentially harmful organisms were not isolated at levels expected to constitute a public health hazard. Information concerning the nature of the product, the total viable count, the presence or absence of pathogenic, toxigenic or indicator organisms, the spectrum of the bacterial flora and the relative predominance of each organism must all be considered when assessing the microbiological acceptability of retail 'ready to eat' products.