Behavior and Inactivation of Enterotoxin-Positive Clostridium perfringens in Pork Picadillo and Tamales Filled with Pork Picadillo under Different Cooking, Storage, and Reheating Conditions

This study analyzed the behavior of Clostridium perfringens in individual ingredients and tamales containing different pathogen concentrations upon exposure to different temperatures and methods of cooking, storage, and reheating. In ground pork, C. perfringens cells were inactivated when exposed to 95°C for 30 min. Three lots of picadillo inoculated with 0, 3, and 5 log CFU/g C. perfringens cells, respectively, were exposed to different storage temperatures. At 20°C, cell counts increased 1 log in all lots, whereas at 8°C, counts decreased by 2 log. Four lots of tamales prepared with picadillo inoculated with 0, 2, 3, and 7 log CFU/g prior to the final cooking step exhibited no surviving cells (91°C for 90, 45, or 35 min). Four lots of tamales were inoculated after cooking with concentrations of 0, 0.6, 4, and 6 log CFU/g of the pathogen and then stored at different temperatures. In these preparations, after 24 h at 20°C, the count increased by 1.4, 1.7, and 1.8 log in the tamales inoculated with 0.6, 4, and 6 log inoculum, respectively. When they were stored at 8°C for 24 h, enumerations decreased to <1, 2.5, and 1.9 log in the tamales inoculated with 0.6, 4, and 6 log of C. perfringens cells, respectively. However, when the lots were exposed to 20°C and then 8°C, 0.8, 1.8, and 2.4 log changes were observed for the tamales inoculated with 0.6, 4, and 6 log, respectively. Microwaving, steaming, and frying to reheat tamales inoculated with 6 log CFU/g C. perfringens cells showed that the pathogen was inactivated after 2 min of exposure in the microwave and after 5 min of exposure to steam. In contrast, no inactivation was observed after 5 min of frying. The tamales inoculated with spores (7 log most probable number [MPN]/g) showed a decrease of 2 log after steaming or frying, and no survival was observed after microwaving. Tamales inoculated with spores (7 log MPN/g) after cooking were susceptible to microwaves, but 2.4 and 255 MPN/g remained after frying and steaming, respectively.

Microbiological safety of domestic refrigerators and the dishcloths used to clean them in Guadalajara, Jalisco, Mexico

Household refrigerators are a potential pathogen contamination source for foods. An evaluation of the microbiological safety of 200 refrigerators in Guadalajara, Jalisco, Mexico, was made by visual inspection, ATP-bioluminescence levels, indicator microorganisms including Escherichia coli and Staphylococcus aureus, and the presence of Listeria monocytogenes and Salmonella. Additionally, interviews of the owners of the refrigerators were carried out to determine relationships between food storage practices, demographic aspects, and microbiological status. Dishcloths used to clean refrigerators were also analyzed. Operational conditions (cleanliness, fullness, organization, frequency of cleaning, and temperature) were evaluated by trained observers. Results showed deficient cleanliness in 55% of refrigerators, 22% were completely full, 43% very disorganized, 28% were usually cleaned only once in 3 to 6 months, and 53% had internal temperatures >7.1°C. ATP-bioluminescence levels were >300 relative light units on 67 and 74% of shelves and drawers, respectively, indicating that surfaces were dirty according to the luminometer manufacturer. Psychrotrophic aerobic bacteria counts on shelves, drawers, and dishcloths were 6.3, 5.2, and 6.3 log CFU/cm(2); for coliform bacteria, 5.2, 3.9, and 4.7 CFU/cm(2); for E. coli, 3.7, 3.5, and 4.8 CFU/cm(2); and for Staphylococcus aureus, 2.1, 2.5, and 2.3 CFU/cm(2), respectively. L. monocytogenes and Salmonella were isolated from 59.5, 20.5, and 17% and 32.5, 8.0 and 12.5% of shelves, drawers, and dishcloths, respectively. Four Salmonella serotypes and nine serogroups (partially serotyped isolates) were identified. The most prevalent were Salmonella Anatum (39.5%), Salmonella group E1 (19.7%), and Salmonella group E1 monophasic (12.5%). Operational conditions and microbiological status were clearly deficient in sampled refrigerators, highlighting the consequent risk of foodborne disease among users. Educational programs are needed to improve the domestic food safety in Mexico.

Increased tolerance of Vibrio cholerae O1 to temperature, pH, or drying associated with colonization of shrimp carapaces

External surfaces of samples of shrimp carapace were inoculated with Vibrio cholerae and stored at 22 degrees C for 1 h in a moist environment to facilitate their adhesion, or for 24 h to permit their colonization of the material. Colonizing cells showed a higher resistance to the effects of high temperatures, low pH, and desiccation conditions than adherent cells. Periods of 10, 5, and 3 min and 0 s were required to inactivate the pathogen when attached cells were exposed to 50, 60, 65, or 70 degrees C. The corresponding times for colonizing cells were 30, 15, 10, and 1 min. At pH 2.5 numbers of attached V. cholerae were reduced by >5 log after 16 min, whereas the reduction of colonizing cells was only 2.8 log. The survival times of the microorganism on dried carapaces stored at 5 and 22 degrees C were, respectively, 60 and 10 min for adherent cells, and 12 and 4 h for colonizing cells. The increased resistance to the effects of high temperatures, low pH, and desiccation of V. cholerae O1 colonizing shrimp carapaces may have significant implications for food safety and the epidemiology of cholera.

Adhesion and colonization of Vibrio cholerae O1 on shrimp and crab carapaces

The potential of Vibrio cholerae O1 to attach to and colonize the carapaces of shrimp and crabs was evaluated. One million cells of V. cholerae O1 were spread within a circle on the external surfaces of separated carapaces and stored at 22 +/- 0.2 degrees C in a moist environment to permit adherence. Attached vibrios were counted directly by an immunofluorescence technique and by the pour plate technique after detachment of the cells. To study the colonization process, rifampicin-resistant strains of V. cholerae O1 were used. V. cholerae O1 strains, including those resistant to rifampicin, were able to attach to shrimp and crab carapaces. Dorsal crab carapaces showed higher levels of attachment than ventral carapaces. Colonization of V. cholerae O1 on these carapaces was also demonstrated. Both attachment and colonization on the shrimp exoskeleton were optimal at a salinity of 1.0 to 1.5%, a pH of 6.0 to 7.0, and a temperature of 37 degrees C. Less than 2% attachment at 3 degrees C contrasted with >20% attachment at 37 degrees C. Even at 3% NaCl, some attachment was observed. Although attachment percentages may appear low (2 to 20%), they represent significant numbers, about 3.7 to 5.6 log10 CFU per carapace. A rugose V. cholerae O1 strain attached to and colonized the shrimp carapace in a fashion very similar to that of the smooth strain from which it was derived. The ability of V. cholerae O1 to attach to and colonize exoskeletons of edible crustaceans provides a potential means of survival in aquatic environments. Concentrations of vibrios that may be reached on a single crab or shrimp carapace are clearly of concern with regard to public health.