Microbiological Quality of Tofu and Related Products in Canada.

One hundred and fifty-three samples of tofu, related products, and environmental samples comprising 346 sample units were collected from 14 manufacturers across Canada. They were analyzed for coliforms, Salmonella , Yersinia , Staphylococcus aureus , and psychrotrophs. Although S. aureus counts were generally less than 250 cells per g and Salmonella was not detected, levels of psychrotrophs exceeded 106 per g in more than 45% of finished tofu and okara samples, and levels of coliforms exceeded 103 per g in more than 35% of these samples. Yersinia enterocolitica was also isolated from four samples of finished tofu.

Microbiological Quality of Fresh and Frozen Breakfast-Type Sausages Sold in Canada.

A national survey was conducted to determine the overall microbiological quality of fresh and frozen breakfast-type sausages manufactured in Canada. Fresh (61 lots; 55 producers) and frozen (62 lots; 35 producers) were analyzed for aerobic colony counts (ACCs), coliforms, Escherichia coli , Staphylococcus aureus and Salmonella . There was wide variation in aerobic colony count values, but most were in the range of 104 to 107 CFU/g. Detectable levels of E. coli and S. aureus were found in at least one-third of all fresh and frozen sausages. In addition, Salmonella was detected in 14.8% of lots of fresh sausages and 6.5% of lots of frozen sausages. Frozen sausages generally had lower microbial loads than fresh ones. Although no standards or guidelines for breakfast-type sausages are available from the International Commission on Microbiological Specifications for Foods (ICMSF), guidelines published in the literature were applied to ACCs, coliforms and S. aureus for both fresh and frozen sausages.

Clostridium Botulinum in Honey, Syrups and Dry Infant Cereals.

A total of 150 honey, 43 syrup and 40 dry cereal samples were analyzed for Clostridium botulinum spores, each in triplicate quantities of 25 g. The foods were sampled randomly, except for two lots of honey which were potentially associated with illness. Botulinal spores were detected in a sample of honey associated with infant botulism and in a single sample of rice cereal.

Microbiological Quality of Dry Dessert Mixes Sold in Canada.

A study done in 1977-1978, assessed the bacteriological quality of five types of dry desserts including starch-, gelatin- and rennet- based products. One hundred and ninety-seven lots were randomly selected across Canada and analyzed for aerobic colony count, aerobic sporeformers, Bacillus cereus , coliforms, Escherichia coli , Staphylococcus aureus and Salmonella . Micro-biological and practical consideration do not warrant the establishment of standards or guidelines for such products at this time.

Microbiological quality of bottled water sold in Canada.

The microbiological quality of bottled water sold in Canada was evaluated. A total of 114 lots of bottled water, both domestic and imported, were analyzed for aerobic colony count, coliforms, fecal coliforms, and Escherichia coli. No fecal coliforms or E. coli were found. Nineteen (46%) of the 41 lots of domestic purified water were found to exceed aerobic colony count standards and another lot exceeded coliform standards. One lot each of domestic and imported mineral water exceeded coliform standards. If mineral water were governed by the aerobic colony count standards for bottled water, then five lots each of both domestic and imported mineral water would have been found to be unsatisfactory. More surveillance of the bottled water industry in Canada is recommended.

Microbiological Quality of Canadian Frozen Meat Pies.

One hundred and twenty samples of a variety of frozen meat pies were collected from 20 manufacturers across Canada and analyzed for aerobic colony count, coliforms, Salmonella , Clostridium perfringens , Staphylococcus aureus , and yeasts and molds. Salmonella was not isolated from any of the pies and only low numbers of C. perfringens and S. aureus were found. The highest aerobic colony count, coliforms and yeasts and molds were observed in pies with uncooked pastry. The degree of contamination in these pies was not alarmingly high to warrant establishment of microbiological standards or guidelines for these products.

Recovery of Fecal Coliforms and of Escherichia coli at 44.5, 45.0 and 45.5°C.

Recovery rates of fecal coliforms and of Escherichia coli were determined at 44.5, 45.0 and 45.5°C in raw milk, ground meat and raw sewage. MPN values based on gas production (Standard MPNs) and on gas production and/or growth only (Total MPNs) were calculated for both fecal coliforms and for E. coli . The expected trend towards lower MPN values with increasing incubation temperature was more pronounced for the Standard MPNs than for the Total MPNs. The temperature effect was also strongly product - specific in that the Total and Standard MPNs for the fecal coliforms and the Standard MPNs for E. coli for sewage only differed significantly from one another within each determination at the three different incubation temperatures. The effect of length of incubation time on the ratios of E. coli to fecal coliforms was most pronounced at 45.5°C. Product specificity was again observed. The greatest increase in the recovery rate of aerogenic E. coli between 24 and 48 h of incubation time occurred in sewage (66%). For meat, the increase was 57% and for milk 46%. In terms of combined (aerogenic and anaerogenic) E. coli (expressed as Total MPNs), the increases were considerably less, but highest for the meat (33%), followed by sewage (29%) and by milk (21%). A breakdown of the E. coli isolates recovered from both gas-positive and gas-negative primary (fecal coliform) EC broth tubes showed that for the three products combined there were eight times as many false-positives at 44.5°C as at the other two incubation temperatures. In contrast, there were 12% false-negatives at 45.5°C compared to 3% at 45.0°C and 2% at 44.5°C. Since the high incidence of false-negatives (loss of E. coil ) at 45.5°C is not counter-balanced by an enhanced specificity (fewer false-positives) over 45.0°C, the latter temperature is to be preferred. Meat yielded the lowest rate for false-positives at any of the three incubation temperatures. In contrast, at 45.5°C, it gave 21% false-negatives compared to only 9% for sewage and 10% for milk. On the other hand, milk contributed the most false-positives at 44.5°C (20%), compared to only 1% for meat and 3% for sewage. A potential loss of 21% of E. coli - containing EC broth tubes is hardly tolerable, reinforcing the contention that gas formation at evaluated temperatures is not a valid criterion of fecal origin.

Microbiological Quality of Frozen Cream-Type Pies Sold in Canada.

Ten types of frozen cream-type pies, manufactured in Canada and imported from the United States, were analyzed for aerobic colony counts, yeasts and molds, coliforms, Escherichia coli , Staphylococcus aureus and Salmonella . The variations in counts depended more on the manufacturer than on the type of pie and the ingredients used. Five of the 465 examined pies had an excess of 105 aerobic colony counts/g, whereas the median value for all the pies examined was between 102 and 103 CFU/g. E. coli and S. aureus were present in few pies, mainly made by one manufacturer, but there was no correlation between high aerobic colony counts and these organisms. Salmonella was not found in any of the pies. Percentage distributions of the estimated 'population' of pies available nationally at the time of the survey were statistically determined. These were then compared with suggested national guidelines in the form of a three-class acceptance plan based on United States surveys and desirable manufacturing practices. These indicate that pies should contain aerobic colony counts of <50,000/g, yeast and mold counts of <500/g, S. aureus counts of <100/g, coliform counts of <50/g, E. coli counts of <10/g, and no Salmonella . Three of the six manufacturers would have had an estimated 5.4 to 32.6% of lots in excess of the guidelines at the time of the survey.

Microbiological Quality of Pasta Products Sold in Canada.

Four hundred and ninety-nine samples of Canadian manufactured pasta and 130 samples of imported pasta were analyzed by standard procedures for aerobic colony counts, Staphylococcus aureus , coliforms and Escherichia coli , Salmonella and yeasts and molds. The microbial quality of these products varied considerably. One imported and two domestic products were contaminated with Salmonella . Based on the analytical results, a three-class plan for microbial guidelines for pasta is proposed in which four parameters determine the acceptability of a product.

Microbiological Guidelines and Sampling Plans for Dried Infant Cereals and Powdered Infant Formula from a Canadian National Microbiological Survey.

The microbiological safety and quality of 130 lots of domestic and imported dried infant cereals and powdered infant formulae were determined using aerobic colony count (ACC), aerobic sporeformers, confirmed and fecal coliforms, Escherichia coli , Staphylococcus aureus , Bacillus cereus , Clostridium perfringens (spores), hemolytic streptococci and yeast and molds. Based on the analytical results and sampling procedures of this survey, no health hazards were found. The results were also used to develop a three-class acceptance plan for ACC (n = 5, c = 2, m = 103/g, M = 104/g), confirmed coliforms (n = 5, c = 1, m = < 1.8/g, M = 20/g) and Salmonella (n = 20, c = 0, m = 0, M = 0). These plans were influenced by the proposed Codex Code of Hygienic Practice for Foods for Infants and Children. Canadian-produced infant foods had an estimate lot rejection rate based on the three-class acceptance plan of 1.1 to 20.3%, based on cereal type and test organism.

Identification of enterotoxin E.

Identification of a new enterotoxin was accomplished by purification of the enterotoxin produced by staphylococcal strain FRI-326 and by preparation of specific antitoxin to the enterotoxin. Toxicity of the preparations was determined in rhesus monkeys, and specificity of the enterotoxin-antitoxin reaction was determined in gel diffusion plates. The enterotoxin was designated enterotoxin E.

Relationship between staphylococcal antiserum titer and zone development on immune serum plates.

A workable relationship was established between the standard serum titers of staphylococcal immune antisera and the development of precipitin zones on serum agar around colonies of staphylococcal strains producing homologous antigens (enterotoxins). The standard titer of a serum is defined as the reciprocal of that serum dilution which, with 10 mug of pure enterotoxin per ml, will give a precipitin zone 10 mm in length in single gel-diffusion tubes after 7 days of incubation at 25 C. A numerical scale was set up for determining the intensity of precipitin zones on serum agar. A reading of 3 was considered optimum. This correlated well with a standard serum titer of 25, when 1 ml of such a serum was used per 20 ml of medium per serum plate. From this relationship, the minimum volume of serum required to give optimum precipitin zone development can be calculated.

Production of staphylococcal enterotoxins A, B, and C in various media.

The effect of initial pH and of length of incubation time at 37 C in four different growth media on the production of staphylococcal enterotoxins A, B, and C was determined. A starting pH of 6.8 gave higher yields of enterotoxins B and C than either pH 6.0 or 5.3. The production of enterotoxin A was, however, not materially affected by the low initial pH of 5.3. Prolonged incubation (48 to 72 hr) resulted only occasionally in higher yields of enterotoxin. The effect of the media on the amount of enterotoxin produced is considerable. Difco Brain Heart Infusion (BHI) was inferior to either Fisher BHI, 4% NZ Amine (NAK), or 3% NAK plus 3% protein hydrolysate powder at the three initial pH values, regardless of length of incubation time. The slight effect of the low starting pH on the production of enterotoxin A is being further investigated.

Relationships among coagulase, enterotoxin, and heat-stable deoxyribonuclease production by Staphylococcus aureus.

The relationship between heat-stable deoxyribonuclease and coagulase production was investigated in the interest of developing more rapid diagnostic and quantitative procedures for distinguishing toxigenic and pathogenic staphylococci from closely related saprophytic organisms.

Some properties of heat-resistant and heat-sensitive strains of Clostridium perfringens. I. Heat resistance and toxigenicity.

Heat resistance at 100 C (D-values), sporulating ratios, toxigenicity for mice, and lecithinase activity (as micrograms per milliliter of enzyme, ascertained by the lecithovitellin reaction) were determined for four strains of Clostridium perfringens. A definite inverse relationship between thermal resistance and toxigenicity was found. The D-values ranged from 17.6 for the most heat-resistant strain to 0.3 for the strain possessing the least heat resistance, with corresponding lecithinase activities from 25 to 133 mug/ml of enzyme. The sporulating ratios did not differ greatly between the strains. The heat stability of the toxin was greater at 100 C than at 75 C. There was a noticeable difference between the heat stabilities of the toxin in the culture fluids of the heat-sensitive and heat-resistant strains at pH 7.0 when the toxic filtrates were held at 100 C. At a holding temperature of 75 C, a similar but lesser difference was observed at pH 5.5. Heat resistance and lecithinase activity did not change when a substrain of the least heat-resistant parent strain was obtained through heat selection by a single transfer, or when the most heat-resistant strain was transferred serially 12 times.

Mice and monkeys as assay animals for Clostridium perfringens food poisoning.

Spores and vegetative cells of Clostridium perfringens, in combination with meat or starch paste, sterile culture filtrates, lecithinase, and phosphorylcholine, were administered to mice and rhesus monkeys in an attempt both to evaluate the animals as test agents and, if possible, to elucidate the active factors producing food-poisoning symptoms caused by this organsim. Some of the preparations were administered to the monkeys by stomach tube; others, in gelatin capsules which were treated with formaldehyde so that the release of their contents was delayed and presumably reached the intestines of the animals. Any changes in intestinal passage times and in consistency of stools of the animals were observed, and the counts of C. perfringens in the feces of the monkeys previous and subsequent to treatment were recorded. The results obtained were inconclusive. Diarrhea occurred only relatively infrequently in both species, regardless of the substance fed or the mode of administration. The changes in intestinal passage times were not great, although in the monkeys there appeared to be a slight trend toward reduction as the magnitude of the bacterial load increased. Phosphorylcholine appeared to have little, if any, effect in reducing intestinal passage time of mice or monkeys. No procedures explored in these experiments could be said to be satisfactory as a means of animal assay for food poisoning strains of C. perfringens since typical symptoms did not appear with regularity.