Predictive modelling of food safety with particular reference to Clostridium botulinum in model cured meat systems.
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Biomedical subjects
Publications and source records attributed to T A Roberts.
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In an outbreak of type C botulism in a group of captive primates, six squirrel monkeys, six white throated capuchin monkeys and two weeper capuchin monkeys succumbed rapidly and died. Clostridium botulinum type C toxin was detected in the remains of the chopped chicken feed and in nine of 11 blood samples and one of three stomach contents samples from the affected animals.
Growth rates of a mixture of Salmonella serotypes inoculated on beef from a commercial abattoir were measured at chill temperatures. The minimum recorded mean generation times were 8.1 h at 10 degrees C; 5.2 h at 12.5 degrees C and 2.9 h at 15 degrees C. Growth did not occur at 7-8 degrees C. From these data the maximum extent of growth of Salmonella during storage of meat for different times at chill temperatures was calculated. Criteria for deciding safe handling temperatures for meat are discussed. Maintaining an internal temperature below 10 degrees C during the boning operation would be sufficient to safeguard public health requirements.
Minced (ground) beef from three supermarkets, three intermediate-sized chain butchers and three small family butchers in each of three geographical areas was examined three times in warm weather and three times in cool. The total viable count (37 and 20 degrees C), numbers of Enterobacteriaceae (37 and 17 degrees C), and presumptive coliforms did not differ significantly between shop type or season. Statistically significant differences in numbers of faecal Streptococci, Staphylococcus aureus and Clostridium perfringens were too small to be of commercial importance, or diagnostic value.
Several sites on commercial beef, pork and lamb carcasses were sampled at the end of the slaughterline. Total viable counts (TVC) of bacteria were assessed by incubation at 37, 20 and 1 degree C in addition to presumptive coliforms (PC), Enterobacteriaceae (ENT) and faecal streptococci (FS). Statistical analyses showed consistently dirty sites within an abattoir but these sites varied from one abattoir to another. Inter-site differences were unaffected by the incubation temperature of the TVC. Numbers of PC, ENT and FS did not mimic TVC. Empirical sampling plans are proposed to detect the highest count on a carcass by bulking samples from known dirty sites. At the end of the slaughterline TVC 37 degrees C is the most useful bacteriological index.
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The NaCl tolerance of different strains of Clostridium botulinum varies over a wide range, and the patterns of NaCl inhibition differ distinctly and characteristically from strain to strain. The more radiation-resistant strains, such as 33A, 62A, and 7272A, are more resistant to NaCl, whereas the more radiation-sensitive strains, such as 51B and 1304E, are more sensitive to NaCl. This rule appears to hold irrespective of whether the spores were unirradiated controls or whether they were radiation damaged prior to exposure to NaCl in the recovery media. The data seem to indicate that radiation doses in the shoulder portion of the radiation survival curves did not noticeably sensitive the spores to NaCl, whereas radiation doses in the exponential-decline portion of the survival curve invariably produced a distinct sensitization. Thus, strains 33A and 62A were not sensitized to NaCl by 0.3 to 0.4 Mrad, i.e., in the shoulder portion of the survival curve. Radiation-sensitive strain 51B, which shows no distinct shoulder in its survival curve, was sensitized to NaCl by 0.1 Mrad, the lowest radiation dose employed in this study. These observations seem to suggest a possible relationship between deoxyribonucleic acid repair capacity and salt tolerance.
An outbreak of type C botulism involving three-week-old broiler chickens on deep litter is described. No direct source of toxin was found. Cl botulinum type C was distributed widely in the litter, and several thousand per gram were demonstrated both in the litter and in the intestinal contents of chicken.
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An outbreak of acute paralysis in a pack of foxhounds, which followed the ingestion of raw and partially cooked meat, was almost certainly due to botulism. Botulinal toxin was detected in the serum of one of three hounds which recovered, and Clostridium botulinum type C was present in a sample of meat remaining from a batch fed to the hounds.
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