Some aspects of bacterial contamination of hands of workers in food service establishments.

In 28 kitchens of restaurants and 10 kitchens of institutions, the hands of 280 persons were sampled in order to determine the role which hands play in contaminating food during preparation. The presence of salmonellae and the number of Enterobacteriaceae and Staphylococcus aureus in these samples was examined. No salmonellae could be isolated. However, large numbers (greater than 10(5)/hand) of Enterobacteriaceae and Staphylococcus aureus occurred on about 8% of the hands. "Normal" washing of the hands resulted in a lower number of transient micro-organisms. Since washing did not influence the number of Staphylococcus aureus on the hands, this organism seems to behave more as a resident organism. Prepared foods such as salads, fried meat and bread were often handled with relatively highly contaminated hands.

Gordon memorial lecture. Poultry disease and public health.

The development of the poultry industry and the consumption of poultry meat is traced over the past quarter of a century and related to the increased incidence of food poisoning in man. Factors affecting the spread of the main poultry pathogens which are of human significance are discussed. The pathogens considered are salmonella, campylobacter, staphylococci and clostridia. Various preventative measures are considered including rearing procedures for poultry, decontamination methods and education of the public. It is concluded that one of the most effective measures is irradiation of poultry and poultry products. The difficulties of introducing this control measure are recognised. It is concluded that more effective application of existing control methods would greatly reduce the hazards to public health.

[Trichinella spiralis as a teacher or the parasite-host relationship between a threadworm and an institute]. / Trichinella spiralis als leermeester of de parasiet/gastheer relatie tussen een haarworm en een instituut.

The present paper provides a review of activities of the National Institute of Public Health in the field of studies on Trichinella spiralis in man and animals. The development of a system of (immune) surveillance of infections due to Trichinella in pigs has been central since the early sixties. Both the fluorescent antibody technique introduced in 1967 and the enzyme-linked immunosorbent assay (ELISA) published in 1974 are examples of these efforts. The method was standardised and, specifically, the ELISA method was mechanized. Comparative studies were done as part of the activities of the EEC working party concerned with trichinosis. The two methods were officially accepted by the EEC. Studies in the slaughter-house as well as in the piggeries (so-called 'in process control') are possible on the basis of the ELISA technique, in which method interest is also being taken in the United States today. Conceivably, industry in Europe will also become interested in the principles of good manufacturing practice, in which certification of slaughtered animals, based on negative results of ELISA studies (without any further inspection in the slaughter-house) will be possible in theory. In addition to the object directly aimed at, i.e. improvement of the method of detection in pigs, designed to prevent human trichinosis, studies on the parasite Trichinella spiralis centered, among other things, on closer examination of the immune response and effector mechanisms in regard to this nematode infection, in which particularly studies on the role of so-called intestinal mast cells produced interesting new views on the subject of (immunological) regulation.

[People are always saying...]. / Die Leute sagen immer...

In his address, delivered on the occasion of his farewell as extraordinary professor of food microbiology and hygiene at the University of Agriculture in Wageningen, the author discussed a number of features of current problems in the field of disease caused by foods. It was pointed out that the risks constituted by chemicals and additives in foods are usually strongly exaggerated by consumers, whereas there is far too little understanding of and information concerning infectious diseases which are transmissible to man by foods. As regards this last-mentioned fact, attention is drawn to the increase, and that which can be anticipated, of cases of food infection and poisoning in Europe. It was stressed that the consumer is an important factor in regard to these forms of disease in view of the fact that a large proportion of these infections may be prevented by a number of relatively simple measures such as cooling or heating of food and adequate hygiene in the kitchen.

Reference material for the evaluation of a standard method for the detection of salmonellas in foods and feeding stuffs.

To evaluate a standard salmonella isolation method a reference material consisting of 0.2 g spray-dried milk inoculated with Salmonella typhimurium and contained in gelatin capsules was prepared. The organisms were distributed homogeneously between capsules, and their numbers were stable for 120 d when the capsules were stored in dry conditions at 4 degrees C. Addition of these capsules with or without food samples to pre-enrichment broth gave low and reproducible levels of Salm. typhimurium contamination without altering the pre-enrichment and without influencing the other bacterial flora present. As a result of an interlaboratory trial, the reference material indicated that the food and/or its competitive flora may have a negative influence on the detection of salmonellas.

Collaborative study on the isolation of salmonella from artificially contaminated milk powder.

The suitability of artificially contaminated milk powder as a substrate for salmonella reference samples and its stability under different storage conditions were studied. The need for a reconstitution step in the standard isolation method for salmonellas from milk powders was also investigated. When milk powder was examined in this way with a reconstitution step, differences in laboratory methods and/or storage times had no significant effect on the results after storage at 4 degrees C. With powder stored at room temperature there was a systematic decrease in the number of samples positive as the storage time increased. It is concluded therefore that milk powder contaminated with salmonellas should be stored at 4 degrees C. Examination of such milk powder with a reconstitution step yielded better results than without it and this step is therefore necessary for improving the reproducibility of the method. No significant differences were encountered between the standard isolation method and that used in the authors' laboratories. The results of this study indicate that milk powder is suitable as basic material for reference samples and that a reconstitution step should be included in the standard salmonella isolation procedure.

[Microbiological studies of beef tartar]. / Microbiologisch onderzoek van filet américain.

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.

Microbiological sampling of towels: comparison of 7 methods.

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.

Microbiological studies on hamburgers.

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 10(6) to 10(8) per g, counts of Enterobacteriaceae from 10(4) to 10(6) per g, of Escherichia coli from 10(3) to 10(5), of group D streptococci from 10(2) to 10(4), of Staphylococcus aureus from 3 to 10(2) and of Clostridium perfringens less than 10 bacteria per g. Of the samples, 32% contained salmonellas; the highest most probable number was 10(2) 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 10(5) to 10(7) per g, and counts of Enterobacteriaceae from 10(2) to 10(5) 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 degrees C. Some were grilled and some fat fried. The total bacterial counts were from 10(3) to 10(5) per g, and counts of Enterobacteriaceae below 10(2) per g. 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 degrees 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 degrees C in a water bath) gives a reduction in the numbers of salmonella of about 4 x 10(3), after which cooking gives a further reduction as mentioned above.

Microbiological aspects of washing hands in slaughter-houses.

The hand hygiene of workers in a number of chicken-, pig-, calf- and cattle slaughter-houses was investigated. The number of E. coli and salmonellae on hands was determined before and after washing hands in order to measure the washing effect on the number of these faecal bacteria. All workers examined carried E. coli on their hands during work. The average logarithmic E. coli count on hands before washing was about 5.0 in chicken-and calf-slaughter-houses, about 3.5 in pig-and 3.0 in cattle-slaughter-houses. Hand washing decreased the E. coli count per hand by about 1.5 log cycle. Salmonellae were isolated from the hands in chicken- (59 pos./145 samples), pig-(42 pos./116 samples) and calf-slaughter-houses (11 pos./68 samples). Even after washing salmonellae were found to be present. Generally 'normal' washing causes a considerable reduction in the number of transient bacteria on hands. The presence of E. coli and Salmonella after washing, however, indicates that the effectiveness of the procedure needs to be improved.

Some aspects of microbial contamination of hands of workers in food industries.

With regard to food hygiene, the question is posed whether carriers of pathogenic organisms, like Salmonella can contaminate a product by their hands. This might especially be possible in case of bad toilet hygiene. Experiments were carried out in 13 food and 3 non-food establishments. An inquiry was made into habits of toilet use and hand washing. The following microbiological examinations were performed on workers' hands: total colony-forming-units per hand, and the presence of Salmonella, E. coli, Enterobact., Staph. aureus, faecal Streptococci and Cl. perfringens. Approximately 42% of workers in the food industry and approximately 64% of workers in other industries seems to use the factory toilet regularly for defaecation. Because of the presence of contaminated raw materials in food industries, it is impossible to get direct proof that faecal contamination of the hands is due to toilet use. However, there is indirect evidence that contamination of workers' hands by raw materials, especially of animal origin, is of much more importance than the consequences of toilet use. This is shown by the occurrence of Salmonella on the hands (5-36% pos.) in only those factories where raw materials of animal origin are handled, by the low incidence of E. coli on the hands in food industries where "clean" materials (vegetables, biscuits, chocolate) are handled, and by the total absence of E. coli on the hands of workers in two non-food industries.