Two Salmonella enrichment media, modified Rappaport's medium (RV) and Muller-Kauffmann medium according to the ISO formula (MK), as well as 4 inoculum ratios (0.1:10, 1:10, 0.1:100 and 10:100 ml pre-enrichment culture/selective enrichment medium) were compared. For this purpose 73 samples of filet américan (raw beef with a mayonnaise sauce) and minced meat, known to contain Salmonella, were analysed using the MPN procedure. Part of the filet américan samples were artificially contaminated with Salmonella and competing flora.

Pull-out roller towels were infected with bacteria and examined with 5 non-destructive methods. In addition to three traditional methods, the agar contact method (A), the swab method (S) and the tape method (T), two lesser known methods have been applied: the rinsing box method (R), new developed in the laboratory, and the filter method (F). In the first (R), the towel is fixed between the lid and the cup of a metal box containing a rinsing liquid; shaking the box completes the test. In the second (F) the liquid is forced through the towel by vacuum. In both experiments the rinsing liquid is tested for contamination. Destructive methods, mainly with a peristaltic blender ("stomacher") (P) or rotary mixer (M), were used as reference for calculating ratios of recovery. With the methods A, S and T, a low ratio of recovery, resp. 5, 10 and 2%, was obtained for Escherichia coli and Staphylococcus aureus. With method R, ratios for the two species were 60-90%, and also for a Micrococcus species and for spores of Bacillus subtilis. With method F the ratio for E. coli and Micrococcus sp. was even slightly higher than 100%. Recovery with method M was about the same as with P. It is concluded that the rinsing box method as well as the filter method are well suited to the purpose of microbiologically testing towels; the lower recovery of the first is compensated by its simplicity.

Two hundred lots of 'filet américain' (a mixture of minced meat, acid sauce, condiments, salt, etc., meant to be eaten raw) were sampled from retailers and examined for several types of micro-organism; 185 lots had been prepared by the retailer, fifteen on an 'industrial' scale. Pork had been used in seventy-three lots (including fourteen 'industrial' lots); beef was present in all lots, horse meat in none of them. On the whole, the bacterial state of the meats in which pork had been used was found to be considerably inferior to that of samples not containing this ingredient. The aerobic bacterial count and number of yeasts, as well as Enterobacteriaceae and group D. streptococci were at least 10 times higher on an average in this case than they were in lots not containing pork. In the case of Lactobacillus, Staphylococcus aureus and Clostridium perfringens the picture was similar, though the counts of the two lastnamed species were smaller. Salmonella was detected in 84 per cent of the pork-containing lots and in 13 per cent of the other lots. For Yersinia enterocolitica, these figures were 44 per cent and 5 per cent, and for Campylobacter fetus, subsp, jejuni 18 per cent and 6 per cent. The pH varied from 5 to 6. Lots containing pork averaged a higher pH. Addition of acid sauce had only a slight effect on pH levels. A number of these results were related to each other. It is concluded that the use of raw pork in meat products meant for raw consumption should be avoided.

Uit steekproeven blijkt de microbiologische kwaliteit van filet americain, waarin rauw varkensvlees is verwerkt, zodanig dat consumptie ontraden kan worden. Dit geldt zowel voor als het produkt door de detaillist is bereid, als wanneer het product industrieel is bereid

Summary One hundred and eighty-two raw, 112 pre-cooked and 750 cooked hamburgers composed mainly of beef or beef and pork were subjected to microbiological examination. Raw hamburgers gave total bacterial counts from 105 to 108 per g, counts of Enterobacteriaceae from 104 to 108 per g, of Escherichia coli from 103 to 105, of group D streptococci from 102 to 104, of Staphylococcus aureus from 3 to 102 and of Clostridium perfringens less than 10 bacteria per g. Of the samples, 32 % contained salmonellas; the highest most probable number was 102 per g but most estimates were below 1 per g. Corresponding figures for the pre-cooked samples were 2–3 log cycles lower, and only one sample contained salmonella. Yersinia enterocolitica was not isolated from any raw or pre-cooked sample. Three hundred and ninety-five of the cooked hamburgers were prepared by grilling raw hamburgers for between 2 and 5·5 min. These gave total bacterial counts from 105 to 107 per g, and counts of Enterobacteriaceae from 102 to 105 per g. Of the samples, 9·4 % contained salmonellas, always in numbers below 1 per g. The remaining 355 cooked hamburgers were prepared from samples pre-cooked for 10 min at 80 °C. Some were grilled and some fat fried. The total bacterial counts were from 103 to 105 per g, and counts of Enterobacteriaceae below 102 perg. Salmonellae, again in small numbers only, were recovered from 3·5 % of samples. When hamburgers were artificially contaminated with Salmonella typhimurium it took 5·5 min on a commercial grill, 2·25 min frying in a frying pan and 1·75 min on a household grill to reliably reduce the salmonella count one hundredfold. This means that at many vending places hamburgers are often cooked for too short a time. D-values were determined for S. typhimurium in hamburger meat at 50, 55, 60, 65 and 70 °C, these values were 7·1, 5·1, 1·2, 0·9 and 0·6 min respectively. It can be concluded that the heating action in the centre of the hamburgers will take place more slowly than in the hamburger as a whole, and that the time between cooking and consumption is very important in reducing the microbial load to acceptable levels. Pre-cooking (10 min at 80 °C in a water bath) gives a reduction in the numbers of salmonella of about 4 × 103, after which cooking gives a further reduction as mentioned above.

Samples (351) of ice‐cream were examined for ‘total aerobic’ colony count, Enterobacteriaceae, coliforms and Escherichia coli. Different methods for the indicator groups were compared. A number of the samples were also examined for Staphylococcus aureus, Bacillus cereus and Salmonella spp. In addition samples were tested microbiologically to detect fraudulently added inhibitory substances. A percentage (31.1) of the samples showed a total count ≤ 10 3 /ml; 11.0% contained > 10 5 /ml. which is the limit laid down in the Dutch Food Law. The MPN of coliforms (without pre‐enrichment) was ≤1/ml in 46.7% of the samples; 7.4% showed MPNs > 10 3 ml. Corresponding figures for Enterobacteriaceae (with pre‐enrichment) were 25.4% and 16.8% respectively. A percentage (33.0) did not meet the present Dutch standard for coliforms. The figures for samples that did not meet the standards of the Food Law are somewhat higher than those found by the Food Inspection Departments, probably because the latter generally investigate more samples from large factories. Staph. aureus and B. cereus were found only sporadically. None of 36 samples, selected because they contained appreciable numbers of indicator organisms, was found to contain salmonellas. Of 100 samples 86% showed inhibitory properties to one or more test micro‐organisms. There was no correlation between a positive test and microbial quality. Sometimes, however, the flavouring agent (lemon and chocolate) seemed to exert an inhibitory activity. The hygienic quality of ice‐cream prepared in large factories was better than that of the other samples. The poor quality sometimes reported for ‘soft’ ice‐cream was not confirmed in our investigations. A typically favourable influence of flavour on bacteriological quality could be demonstrated only for lemon ice‐cream. The same values for MPNs of Enterobacteriaceae were found when overnight pre‐enrichment in buffered peptone water was replaced by 2 h resuscitation in tryptone soya broth. Resuscitation for only 45 min in peptone saline yielded lower results. When followed by an Enterobacteriaceae colony count, overnight pre‐enrichment, 2 h resuscitation in tryptone soya broth or 1 h resuscitation on tryptone soya agar in Petri dishes gave almost the same results. No differences were found in favour of MPNs when compared with colony counts of Enterobacteriaceae. The method found most efficient for the detection of Esch. coli in ice‐cream relies on resuscitation followed by enrichment in brilliant green bile lactose broth at 44°C.

Samples of 61 home grown and 199 imported vegetables of different varieties were examined for Escherichia coli, faecal streptococci and, when E. coli was present, for salmonellas. Eleven per cent of samples contained greater than 10(4) E. coli per 100 g, and 14% greater than 10(6) faecal streptococci per 100 g. Salmonellas were isolated from 23 out of 103 samples examined. Salmonellas were isolated from 8% of 76 samples with E. coli less than 10(4)/100 g, but from 63% of 27 samples with E. coli exceeding 10(4)/100 g; from 6% of 65 samples containing less than 10(6) faecal streptococci/100 g but from 51% of 37 samples containing more than 10(6)/100 g. S. typhi was isolated from one sample of vegetables imported from the tropics. To our knowledge this is the first isolation of S. typhi from food in the Netherlands. Products from tropical countries were found to present the highest level of contamination. The hygienic quality of Dutch products is sometimes inferior to that of similar imported products, although the different seasons of sampling may have influenced the result. For the prevention of risk to the consumer of vegetables, good kitchen hygiene would appear to be the most important factor.