Survival Of Clostridium Perfringens Research Articles

Survival of Clostridium perfringens, Staphylococcus aureus, Listeria monocytogenes and Salmonella enterica in alternatively cured ham during cooking and process deviations

Boneless hams were prepared with four different brines and inoculated on the surface and at a depth of 1 cm with multiple strains of Clostridium perfringens, Staphylococcus aureus, Listeria monocytogenes and Salmonella enterica. Hams were processed with a standard, low relative humidity or interrupted process cycle to an end point temperature of 70 °C. Microbiological populations were determined at the beginning, mid-point and end of the cycles. The change in population was calculated for each bacterium at each time point, by comparing the population to the initial inoculated population. There was no difference in the reductions in bacterial populations for all of the inoculated bacteria attributable to brine type. There were significant reductions in the populations of Staphylococcus aureus, Listeria monocytogenes and Salmonella enterica for both the surface and interior samples which were attributable to the end point temperature. Population reductions for Clostridium perfringens were approximately 1.8 log10 for both the surface and internal samples, and the population reductions for the surface samples were greatest with the interrupted cycle. The low Rh cycle resulted in the least reductions for the surface samples while the greatest population reductions for the surface samples were observed with the interrupted cycle.

Survival of Clostridium perfringens, Staphylococcus aureus and Salmonella enterica in alternatively cured bacon during cooking and process deviations

Pork bellies were injected with four different alternative curing brines. The bellies were inoculated on the surface and at a depth of 1 cm with multiple strains of Clostridium perfringens, Staphylococcus aureus and Salmonella enterica. The bellies were processed using either a standard process cycle or an interrupted process cycle to simulate a process deviation. Additionally, laboratory simulation of the same cycles was conducted where surface inoculated pork belly samples (22 ± 1 g) were processed in a circulating water bath. Microbiological populations were determined at the beginning, mid-point and end of the cycles, and the change in population was calculated for each bacterium at each time point, by comparing the population to the initial inoculated population. Irrespective of the brine or process cycle, the populations of all of the inoculated bacteria on both the surface and interior samples had decreased by the end of the process. There was no difference in the reductions in bacterial populations for all of the inoculated bacteria by brine type or by sample location (P > 0.30). There were differences in the microbial population reductions for C. perfringens attributable to the processing cycle (P < 0.001), with less population reductions associated with the standard cycle when compared to the interrupted cycle. However, no differences (P > 0.10) were observed in the population reductions between the two processing cycles for either S. aureus or S. enterica.

Survival of Clostridium perfringens During Simulated Transport and Stability of Some Plasmid-borne Toxin Genes under Aerobic Conditions

Clostridium perfringens is a pathogen of great concern in veterinary medicine, because it causes enteric diseases and different types of toxaemias in domesticated animals. It is important that bacteria in tissue samples, which have been collected in the field, survive and for the classification of C. perfringens into the correct toxin group, it is crucial that plasmid-borne genes are not lost during transportation or in the diagnostic laboratory. The objectives of this study were to investigate the survival of C. perfringens in a simulated transport of field samples and to determine the stability of the plasmid-borne toxin genes cpb1 and etx after storage at room temperature and at 4°C. Stability of the plasmid-borne genes cpb1 and etx of C. perfringens CCUG 2035, and cpb2 from C. perfringens CIP 106526, JF 2255 and 6 field isolates in aerobic atmosphere was also studied. Survival of C. perfringens was similar in all experiments. The cpb1 and etx genes were detected in all isolates from samples stored either at room temperature or at 4°C for 24–44 h. Repeated aerobic treatment of C. perfringens CCUG 2035 and CIP 106526 did not result in the loss of the plasmid-borne genes cpb1, cpb2 or etx. Plasmid-borne genes in C. perfringens were found to be more stable than generally reported. Therefore, C. perfringens toxinotyping by PCR can be performed reliably, as the risk of plasmid loss seems to be a minor problem.

Impact of Cooking, Cooling, and Subsequent Refrigeration on the Growth or Survival of Clostridium perfringens in Cooked Meat and Poultry Products

In January 1999, the Food Safety and Inspection Service (FSIS) finalized performance standards for the cooking and chilling of meat and poultry products in federally inspected establishments. More restrictive chilling (stabilization)requirements were adopted despite the lack of strong evidence of a public health risk posed by industry practices employing the original May 1988 guidelines (U.S. Department of Agriculture FSIS Directive 7110.3). Baseline data led the FSIS to estimate a “worst case” of 104Clostridium perfringens cells per g in raw meat products. The rationale for the FSIS performance standards was based on this estimate and the assumption that the numbers detected in the baseline study were spores that could survive cooking. The assumptions underlying the regulation stimulated work in our laboratory to help address why there have been so few documented outbreaks of C. perfringens illness associated with the consumption of commercially processed cooked meat and poultry products. Our research took into account the numbers of C. perfringens spores in both raw and cooked products. One hundred ninety-seven raw comminuted meat samples were cooked to 73.9°C and analyzed for C. perfringens levels. All but two samples had undetectable levels (<3 spores per g). Two ground pork samples contained 3.3 and 66 spores per g. Research was also conducted to determine the effect of chilling on the outgrowth of C. perfringens spores in cured and uncured turkey. Raw meat blends inoculated with C. perfringens spores, cooked to 73.9°C, and chilled according to current guidelines or under abuse conditions yielded increases of 2.25 and 2.44 log10 CFU/g for uncured turkey chilled for 6 h and an increase of 3.07 log10 CFU/g for cured turkey chilled for 24 h. No growth occurred in cured turkey during a 6-h cooling period. Furthermore, the fate of C. perfringens in cooked cured and uncured turkey held at refrigeration temperatures was investigated. C. perfringens levels decreased by 2.52, 2.54, and 2.75 log10 CFU/g in cured turkey held at 0.6, 4.4, and 10°C, respectively, for 7 days. Finally, 48 production lots of ready-to-eat meat products that had deviated from FSIS guidelines were analyzed for C. perfringens levels. To date, 456 samples have been tested, and all but 25 (ranging from 100 to 710 CFU/g) of the samples contained C. perfringens at levels of <100 CFU/g. These results further support historical food safety data that suggest a very low public health risk associated with C. perfringens in commercially processed ready-to-eat meat and poultry products.

Survival of Clostridium perfringens and Aerobic Bacteria in Ground Beef Patties during Microwave and Conventional Cookery

Conventional oven cookery was more effective than microwave oven cookery for reducing numbers of aerobic microorganisms and Clostridium perfringens in ground beef patties when the meat was heated to approximately the same internal temperatures of 65–71°C for rare or 77–93°C for well done. Reductions in numbers of C. perfringens during microwave cookery of patties inoculated with 105 vegetative cells/g ranged from 0.75 to 1.48/g (log values); for conventional cookery, these reduction values ranged from 3.51 to 8.06/g (log values). Recovery of heat-stressed cells of C. perfringens was equally efficient in Trypton-Sulfite-Cycloserine agar and Sulfite-Polymyxin-Sulfadiazine agar.

Influence of heating and cooling rates on spore germination and growth of Clostridium perfringens in media and in roast beef.

Spore germination, growth and survival of Clostridium perfringens during heating and/or cooling were examined. The spores in media (FTM or ground beef) were exposed to rising temperature from 20 to 60°C at increment rates of 7-25°C/h or to falling temperature from 60 to 15 or 10°C at decrement rates of 5 to 25°C/h. Roast beef was prepared with various muscles inoculated with the spores. Although germination and growth occurred while heating, the vegetative cells were killed at 60°C in media and in roast beef. During exposure to falling-temperature rates of 25 to 15°C, no change in the population was observed; multiplication of not more than 10-fold at 10°C/h and exponential multiplication at 7.5 and 5°C/h were observed. Roast beef prepared with gluteus, semitendinosus, or halved semitendinosus muscle did not support any growth of C.perfringens during cooling/chilling. That prepared with the whole muscles of semimembranosus supported some growth, but it did not surpass the inoculum size.

Growth and Survival of Clostridium perfringens in Rare Beef Prepared in a Water Bath

The low-temperature, long-time cooking of beef, using either a water bath or a conventional oven, resulted in partial inactivation of Clostridium perfringens vegetative cells. Beef roasts were cooked in a water bath for process times calculated to inactivate low and high levels of C. perfringens vegetative cells. Cooking beef in a water bath to an internal temperature of 60 C and holding for at least 12 min, as required by the USDA, reduced a population of C. perfringens by approximately 3 log cycles. To decrease the risk of subsequent outgrowth of C. perfringens, roasts (⩽ 1.5 kg) may be subjected to a process calculated for a 12-log reduction in population, which would include holding times of 2.3 h or longer at an internal temperature of 60 C. Recommendations are given for cooking and cooling roasts to minimize microbiological problems.

Effect of sample transport systems on survival of bacteria in ground beef

The effects of two transport systems and cryoprotective agents on the survival of bacteria in ground beef samples were evaluated. Survival of Clostridium perfringens in ground beef samples after simulated transport (72 h) was higher (about 99%) in Dry Ice than in Trans Temp shipping units (-3 degrees C). There were no significant differences between the two transport systems in survival of coliforms, Escherichia coli, Staphylococcus aureus, or aerobic bacteria. Mixing ground beef samples at a ratio of 1:1 (wt/vol) with 10, 20, or 30% buffered solutions of dimethyl sulfoxide or glycerol before freezing improved the survival of C. perfringens and coliforms in both transport systems. Recovery of E. coli was significantly higher with the addition of 10% dimethyl sulfoxide before Dry Ice transport. Addition of 10% dimethyl sulfoxide resulted in a 100% recovery of both S. aureus and aerobic bacteria from ground beef after simulated transport in Trans Temp shipping units. The use of cryoprotective agents can improve the survival of bacteria during transport of ground beef samples.

Survival of Clostridium perfringens During Preparation of Precooked Chicken Parts

Vegetative cells of Clostridium perfringens were completely destroyed and the number of viable spores was reduced by procedures used to process precooked chicken thighs and breasts. A mixed inoculum of vegetative cells of C. perfringens CDC strains 7947 and 7948 was killed in thighs and breasts cooked in water at 82 C for 20 min and at 93 C for 15 min. Heat-sensitive spores of C. perfringens strain 7947 were reduced to low levels after 43 min at 82 C and completely eliminated after 38 min at 93 C. Heat-resistant spores of C. perfringens strain 7948 were not reduced when water-cooked at 82 C for 50 min nor completely destroyed after 45 min at 93 C. C. perfringens 7948 spores survived during frozen storage of inoculated thighs which were cooked at 82 C for 20 min (40–50%) and at 93 C for 45 min (23–30%). Numbers of spores were further reduced after reheating frozen pieces at 192 C for 30 min. Thighs were coated with inoculated batter and breading and flash fried at 192 C for 30, 45, or 60 sec resulting in destruction of more than 99% of vegetative cells and more than 90% of heat-resistant spores.

Survival of Clostridium Perfringens on Chicken Cooked with Microwave Energy

Chicken pieces, which had been inoculated with spores or vegetative cells of heat resistant or heat sensitive strains of Clostridium perfringens, were cooked in a microwave oven and browned in corn oil. The effects of freezing, thawing and frozen storage before and after microwave cooking on recovery of vegetative cells and spores were evaluated.Microwave cooking resulted in a two log cycle reduction in resident vegetative and inoculated C. perfringens cells. When chicken pieces were frozen and thawed, prior to microwave cooking, a greater reduction of the microbial load after cooking was found for both cells and spores of C. perfringens. Reduction of spores by microwave energy was minimal, however, the cooking environment provided an efficient activation and germination step.Cells or spores of C. perfringens were not recovered after microwave cooking followed by browning in heated vegetable oil at 190.5° C.

Survival of Clostridium perfringens in Starch Pastes . Studies at Freezer and Refrigerator Temperatures

Survival of Clostridium perfringens in Starch Pastes . Studies at Freezer and Refrigerator Temperatures

Survival of Clostridium perfringens During Baking and Holding of Turkey Stuffing1

Vegetative cells of three strains of Clostridium perfringens were used as inoculum for bread and onion stuffing for eight lightweight and eight heavyweight turkeys. When stuffed turkeys were refrigerated (5 +/- 1 C for 24 +/- 2 hr), a mean count of 580 vegetative cells of C. perfringens per gram of stuffing was reduced to undetectable levels (<6 per gram) in six of the eight. An inoculum of spores of the three strains used in a second series survived refrigerated holding with no change in numbers. During cooking of the stuffed turkeys in an oven at 94 C, numbers of vegetative cells fell steadily and numbers of spores remained constant or increased slightly (2 of 16 stuffings), until the temperature of the stuffing rose above that permitting growth. Viable C. perfringens cells were recovered from the stuffings at the end of cooking plus 1 hr for the group inoculated with the spore suspension. Storage of these stuffings resulted in marked reductions in numbers after 6 days at 5 +/- 1 C and in increases after 24 +/- 2 hr at 23 +/- 1 C. Cells of a strain which produces spores not considered heat-resistant survived in stuffing in birds cooked to doneness in ovens at 94, 163, and 232 C. In accepted methods of cooking stuffed turkeys, C. perfringens contaminants may survive and create a hazard if subsequent storage is in a temperature range which permits their multiplication.