Bacteriological requirements for and bacteriological analysis of precooked (‘instant’) cereals and similar foods

Controlling growth of Streptococcus faecium in a ham model with heat and ethylenediamine tetraacetic acid, tertiary butylhydroquinone or nisin

The study described in this paper was designed to test the effect of heat and EDTA, TBHQ or nisin on the stability of a ham model with regard to Streptococcus faecium. Comminuted ham tissue containing brine and test ingredients was inoculated with two strains of Str. faecium and heated for 0, 30, 60, 90 and 120 min at 68·9°C. Growth was followed during incubation at 7°C and 37°C. In combination with heating at 68·9°C for 30 min, a stable (180 days 7°C) model was obtained by adding (ppm): 400, EDTA; 1000, TBHQ or 20, nisin. EDTA and nisin seem promising compounds for enhancing the stability of pasteurized ham with regard to Str. faecium.

Growth inhibition of heat-injured Enterococcus faecium by oligophosphates in a cured meat model

Cells of two heat-resistant strains of Enterococcus faecium were heated and incubated in meat suspensions containing curing ingredients. The concentrations of the curing ingredients were those frequently used for pasteurized ham-type products, except that the concentrations of the oligophosphates (triphosphate and diphosphate) varied. Heating tests at 69 degrees C were performed with inoculated meat suspensions in heat-sealed plastic pouches. Numbers of bacteria were counted immediately after heating and in parallel series of heated pouches incubated at 37 degrees C. Plating was performed in Tryptone Dextrose Yeast Meat Peptonised Milk Agar (TDYMP); in TDYMP Agar to which the curing ingredients were added; and in TDYMP Agar to which the curing ingredients except oligophosphates were added. The inclusion of oligophosphates in the heating medium increased the heat-injury sustained by the E. faecium cells, and in combination with rather severe heat treatment even completely blocked the growth of surviving organisms in the meat suspension incubated at 37 degrees C. The presence of oligophosphates in the culture medium TDYMP Agar severely reduced the counts of freshly heated cells; however, this effect disappeared after repair and growth of the surviving organisms in the meat suspension.

The potential of vancomycin-resistant enterococci to persist in fermented and pasteurised meat products

Experiments with 148 isolates of vancomycin-resistant enterococci (VRE) were performed to assess their potential to persist and grow in fermented sausages and pasteurised meat products. All strains were meat isolates and Van-type A, except a single VanC1 strain. In total, 143 strains of Enterococcus faecium were involved. Eight selected strains were examined for their potential to grow at high salt and nitrite levels and at reduced pH. The same isolates were used in experiments with fermented sausages. All available strains were subjected to heating tests in meat suspensions with added curing ingredients. All but one of the eight tested isolates grew at pH 4.0 in tryptone soya broth (TSB). With the combination of 8% w/w NaCl, 400 ppm NaNO2 and 0.5% w/w glucose in the meat suspension, all isolates grew at 37 degrees C, whereas none grew at 7 degrees C even after 56 days. With the addition of 10% w/w NaCl, 200 ppm NaNO2 and 0.5% w/w glucose, still one E. faecium isolate grew at 37 degrees C, although very slowly. Overall, the strains tolerated high salt and nitrite concentrations and reduced pH very well, even beyond levels applied in the regular production of fermented and/or pasteurised meat products. The tested strains could be isolated after the fermentation and further ripening of "boerenmetworst" and "snijworst". Overall, their colony counts decreased on average about 1 log-unit over a period of 60 days after batter manufacture. All 148 isolates demonstrated a relatively weak thermal resistance compared to results for selected vancomycin-sensitive enterococci strains reported in the literature and to results collected under identical experimental conditions in this laboratory. None of the strains (log inoculation level about 5-6 ml(-1) for each isolate) could be cultured after heating at 70 degrees C for 10 min.

Attempt in classification of catalase-positive staphylococci and micrococci

Mossel, D. A. A. (Central Institute for Nutrition and Food Research T.N.O., Utrecht, The Nethrlands). Attempt in classification of catalase-positive staphylococci and micrococci. J. Bacteriol. 84:1140-1147. 1962.-About 390 strains of Staphylococcus aureus, isolated from clinical material, and about 190 strains of coagulase-negative staphylococci and micrococci from strictly nonclinical habitats were studied by the following recently recommended biochemical tests: anaerobic dissimilation ("fermentation") of mannitol, gelatin liquefaction, type of growth on tellurite-glycine agar, hydrolysis of urea, and KCN tolerance. The latter three tests appeared either not specific for, or not positive for, most S. aureus strains. Virtually all strains of S. aureus were gelatin-positive, but 71% of the other types of cocci also liquefied gelatin. Rapid anaerobic breakdown of mannitol, however, was shown by ca. 95% of the strains of S. aureus, and late fermentation by an additional 3%. Of 105 obligately aerobic coagulase tive cocci (micrococci), none fermented mannitol; of 40 facultatively anaerobic, coagulase-negative cocci (staphylococci), only 7 (18%) fermented mannitol. Oxidative metabolism of mannitol occurred in only three (<1%) strains of S. aureus but was detected in roughly half of the isolates of both groups of coagulase-negative cocci. Pigmentation was confirmed to be of little value, because roughly 50% of both coagulase-positive and -negative strains showed a pale-yellow color on Chapman's mannitol salt agar while 13% of the S. aureus strains tested were white. A key to the classification of catalase-positive cocci consistent with that currently used for Enterobacteriaceae has been based on these figures.

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

Because 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 taking Salmonella as a model. For this purpose an assessment was carried out of the risk of accepting Salmonella contaminated consignments of foods, despite a negative outcome of (i) examination of 1.5 kg samples for Salmonella; (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 epsilon-factor, defined as c.f.u./g of Enterobacteriaceae/c.f.u./g of Salmonella; 4642 were positive for the former group but ;free' from Salmonella, and the rest were negative in both tests. Numbers of c.f.u./g for both groups, and hence the epsilon-factors, varied widely between commodities and also between different consignments of the same food product. The average for epsilon amounted to 5.8 x 10(3), far from the base-line value of 0.75 x 10(3) assessed 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.

Studies on the estimation of the hygienic condition of frozen broiler chickens

Various sampling techniques to determine the aerobic, E. coli and Enterobacteriaceae counts and to detect the presence of salmonellas were compared. As a simple method for the detection of salmonellas a modified Surkeiwicz procedure using both drip and rinse water is advocated. To evaluate hygiene during processing, determination of the number of Enterobacteriaceae in pieces of skin from the ventral, lateral and breast region is preferred.