The reliability of the examination of foods, processed for safety, for enteric pathogens and Enterobacteriaceae: a mathematical and ecological study

Abstract

SUMMARYBecause of the paucity of quantitative data on numbers of other enteric pathogens in food, the reliability of the examination of processed foods for Enterobacteriaceae was estimated takingSalmonellaas a model. For this purpose an assessment was carried out of the risk of acceptingSalmonellacontaminated consignments of foods, despite a negative outcome of (i) examination of 1·5 kg samples forSalmonella;(ii) examination of one or two 1 g samples for Enterobacteriaceae; (iii) simultaneous application of both tests. The computations were based on the results of the examination of 6830 samples of dried foods, processed for safety, out of a total of 18170 samples.Only 69 samples permitted the exact calculation of the factor, defined as c.f.u./g of Enterobacteriaceae/c.f.u./g ofSalmonella;4642 were positive for the former group but ‘free’ fromSalmonella, and the rest were negative in both tests. Numbers of c.f.u./g for both groups, and hence the factors, varied widely between commodities and also between different consignments of the same food product. The average for amounted to 5·8 × 103, far from the base-line value of 0·75 × 103assessed earlier. In only 0·1% of samples did the Enterobacteriaceae test fail to achieve the required consumer protection.This investigation therefore substantiates that testing foods processed for safety by examining accurately chosen quantities for ecologically well selected and taxonomically thoroughly defined index organisms is a most effective procedure in terms both of consumer protection and simplicity of examination without compelling the food industry to achieve hardly attainable microbiological quality standards.

Comparison of the Effects of Liquid Medium Repair and the Incorporation of Catalase in MacConkey Type Media on the Recovery of Enterobacteriaceae Sublethally Stressed by Freezing

“…Subsequently poured plates with VRBG were made, layering these with about 15 ml of VRBG and incubating for 3 d at 17°C (Mossel & Ratto 1973). A representative proportion of typical colonies was subcultured on to lactose lauryl sulphate agar (Drion & Mossel 1977). This allows pure cultures to be obtained and at the same time an assessment made of the mode of attack on lactose.…”

THE ELIMINATION OF ENTERIC BACTERIAL PATHOGENS FROM FOOD AND FEED OF ANIMAL ORIGIN BY GAMMA IRRADIATION WITH PARTICULAR REFERENCE TO SALMONELLA RADICIDATION1

“…Estimates of E are lo3 -lo5 /g, dependent on type of commodity (Mossel et al 1968(Mossel et al , 1973(Mossel et al ,1974 while E values also vary widely, viz. somehwere between lo4 -l o 6 , once more dependent on type and extent of contamination of the product (Drion and Mossel 1977). A fairly high estimate of E / E could be the order 1; this value has recently been substantiated by us in surveys on the occurrence of Salmonella in 1 g portions of large consignments of minced meat, one of the most severely contaminated types of raw meat in The Netherlands (Edel et al 1975).…”

“…Another significant aspect of the assessment of required doses of ionizing radiation is the use of proper methods for the enumeration of survivor's cfu's. Heated cells, and those exposed to low water activity, reduced pH or lower temperatures have been demonstrated to have incurred sublethal lesions, in the sense that they show a sharply increased susceptibility to many unfavorable external conditions (Mossel 1977). This implies that concentrations of antimicrobial compounds, used in selective media which are of no consequence at all for fully vital cells, limit or even completely inhibit the proliferation of cells of the same organism exposed to any of the listed treatments.…”

“…For calculations in the field of MPED's the parameter E which was introduced a few years ago (Drion and Mossel 1977) is once more quite useful. It is defined as the proportion between the numbers of cfu's of Enterobacteriaceae and of Salmonella per gram of the same material.…”

Rapid Detection of Excessive CFU Counts of Enterobacteriaceae, S. aureus and Yeasts by Nitrate Reduction/Glucose Dissimilation (NGD) Monitoring in Selective Media

“…The pellets obtained are suspended in three selective media: sodium lauryl sulfate broth (Drion and Mossel, 1977), a modified Baird Parker liquid medium (van Doome et al, 1981), and oxytetracyclin gentamicin glucose broth (Mossel et al, 1975). For detailed composition of media, refer to the Appendix.…”