Levels and enterotoxigenicity of Clostridium perfringens in pozole, tamales, and birria.

A quantitative survey of Clostridium perfringens in typical foods served at local restaurants was conducted for 18 months in Guadalajara, Mexico. A total of 151 samples, including goat's birria (50), pozole (50), and beef tamales (51), were collected from small restaurants in Guadalajara. Samples were tested for C. perfringens by the most probable number (MPN) method and for mesophilic aerobic plate counts (MAPCs) and coliform, yeast, and mold counts by plate count methods. Isolates confirmed as C. perfringens were further sporulated and tested for cytotoxic or cytotonic effect against Vero cells as an indication of enterotoxin production. C. perfringens was detected in 78 (52%) of all samples at concentrations that ranged from 2.3 to 5.4 log MPN/g. Average MAPCs were 1.3 to 2.7 log CFU/g, depending on the type of dish. Coliform counts ranged from less than 1.0 to 1.5 CFU/g, and yeast and mold counts were less than 1.0 log CFU/g in all cases. A total of 118 isolates of C. perfringens were tested for enterotoxic effect on Vero cells; 82 (70%) showed activity against Vero cells. Of them, 31 isolates induced cell lysis, indicating cytotoxic effect; 41 induced cell elongation, indicating cytotonic effect; and 10 produced both cytotoxic and cytotonic effect. Dilution of the bacterial filtrates that were still producing an effect on Vero cells ranged from 1:80 to 1:5,120. These results underscore the importance of determining enterotoxigenicity when testing for C. perfringens in foods.

Isolation of Arcobacter spp. from retail meats and cytotoxic effects of isolates against vero cells.

A survey of Arcobacter spp. was conducted over a 12-month period in Guadalajara, Mexico. A total of 135 samples (45 lean ground beef samples, 45 lean ground pork samples, and 45 chicken samples, including drumsticks, gizzards, and ground or chopped breast) were collected from local butcheries. The samples were enriched in Johnson-Murano enrichment medium and then streaked onto Johnson-Murano agar plates. Typical colonies were subjected to microscopic and biochemical identification followed by polymerase chain reaction confirmation of the genus Arcobacter. All isolates confirmed to be Arcobacter isolates were then inoculated into Eagle's minimum essential medium to determine their cytotoxicity against Vero cells. Arcobacter spp. were detected in 28.8, 51.1, and 40.0% of beef, pork, and chicken samples, respectively. From these samples, 101 isolates were confirmed to be Arcobacter spp. by polymerase chain reaction. Overall, the species most frequently identified was A. butzleri, followed by A. skirrowii. A. cryaerophilus was isolated only from pork meat. Ninety-five (95%) of the Arcobacter isolates produced a virulence mechanism against Vero cells, and 38 of them induced cell elongation, indicating enterotoxin production. Eighteen isolates produced the formation of vacuoles, and 39 produced both vacuolization and elongation. The vacuolization effect may be related to a vacuolizing toxin. The production of a vacuolizing toxin by Arcobacter spp. has not previously been reported. Results obtained in this study indicate that Arcobacter spp. may show cytotoxic effects other than the recognized enterotoxin production.

Antagonismo de cepas de Streptococcus Lactobacillus y Leuconostoc procedentes de quesos frescos no pasteurizados contra algunas bacterias enteropatogenas. / Antagonism of Streptococcus, Lactobacillus and Leuconostoc strains isolated from fresh raw cheeses against some enteropathogenic bacteria

Diez cepas de cada uno de los generos Streptococcus, Lactobacillus y Leuconostoc, fueron aisladas de quesos frescos no pasteurizados del comercio, y determinada su capacidad para antagonizar 13 cepas de Staphylococcus aureus, 13 de Salmonella (3 serotipos) y 13 de Shigella (dysenteriae, flexneri, sonnei y boydii). El efecto antagonico se determino con base a la capacidad para inhibir el desarrollo del patogeno sobre placa de agar APT inoculada con la bacteria lactica. Los primeros se probaron a dos niveles: aproxidadamente 4 veces mayor y 30 veces menor que la del lactico en las zonas de contacto. Todas las cepas se mostraron muy activas excepto 4 de Lactobacillus, con nulo efecto hacia las 33 de patogenos, y 2 de Leuconostoc que resultaron ineficientes contra las 13 de Shigella. El Streptococcus presento la mayor y mas consistente capacidad antagonista incluidos los inoculos altos del patogeno. Entre estos, las cepas de Shigella (con la salvedad anotada) exhibieron la mayor susceptibilidad. La manifiesta capacidad antagonista de las bacterias lacticas que forman parte de la flora natural de la leche cruda, contribuye a explicar el limitado papel de los quesos frescos no pasteurizados en la incidencia directa de gastroenteritis en la poblacion