Influence of different processing procedures on the reproductive capacity of Trichinella spiralis in pork meat.

The aim of this work was to determine the influence of different processing procedures and preparations on the viability and infectivity of Trichinella spiralis ML. The muscles of limbs tongue and masseters of pigs experimentally infected were collected, splitted to pieces, and pooled. Five batches were used for the following processing procedures: (1) seasoning with "adobo", commercially acquired chilli and several other spices, (2) "wet-curing" by immersion of meat pieces in 3% brine during 24 hours, (3) cold storage without any further processing or preparation, (4) freezing to -20 degrees C and, (5) drying for 24 hours at 60 degrees C. Samples were stored at 4 degrees C for 15, 45, 60, 75, 90, 105 or 266 days after preparation. At the last-mentioned dates, ML were recovered and used to determine the reproductive capacity by infecting naïve mice. The state of meat conservation or spoilage respectively was tested by visual and tactile examination. In samples treated by freezing or drying no motile larvae were found after artificial digestion and, following inoculation of mice with larvae recovered from these groups, no ML were founded after 40 days of infection. After the artificial digestion of the cold stored samples, the ones seasoned with "adobo" and "wet-cured", a number of motile ML were consistently obtained. Initial reproductive capacity index was as of 80+/-0.5, then rates decreased to 60 - 70 between days 15 and 105 PT and dropped to 40+/-6.7 at day 266 for seasoned, 33+/-2.7 for cold-stored and 33+/-2.5 for cured samples. The influence of storage time (p=0.000005; factorial ANOVA) but not for processing procedure (p=0.724; factorial ANOVA) were statistically significant. The sensorial examination of the meat samples showed severe changes caused by spoilage in odour, texture and colour from day 45 of storage. Data reported from this trial proves that curing or flavoring do not inactivate the Trichinella Mexican strain, although cold storage for more than three months led to a partial decrease of the reproductive capacity. Freezing and drying seemed to be effective measures to eliminate the ML infectivity.

Isolation and characterization of Shiga toxin-producing Escherichia coli O157:H7 and non-O157 from beef carcasses at a slaughter plant in Mexico.

The contamination of beef carcasses with Shiga toxin-producing O157:H7 and non-O157 Escherichia coli (STEC) obtained from a slaughter plant in Guadalajara, Mexico was investigated. A total of 258 beef carcasses were sampled during a 12-month period. All samples were assayed for STEC by selective enrichment in modified tryptone soy broth supplemented with cefixime, cefsulodin and vancomycin, followed by plating on Sorbitol MacConkey Agar supplemented with cefixime and tellurite (CT-SMAC). Simultaneously, all samples were assayed by immunomagnetic separation (IMS) and plated on CT-SMAC and CHROMagar. The presence of the stx1, stx2, eaeA and hly933 genes, recognized as major virulence factors of STEC, was tested for O157:H7 and non-O157 E. coli isolates by multiplex polymerase chain reaction (PCR). STEC was detected in two (0.8%) samples. One of these STEC isolates corresponded to the serotype O157:H7 showing stx2, eaeA and hyl933 genes. The other isolate corresponded to non-O157 STEC and only had the stx1 gene. Thirteen carcasses (5%) were positive for nonmotile E. coli O157 and 7 (2.7%) were positive for E. coli O157:H7. The presence of O157:H7 and non-O157 STEC on beef carcasses in this slaughter plant in Guadalajara, Mexico, emphasizes the importance of implementing the Hazard Analysis and Critical Control Point (HACCP) system, as well as the need for implementing, evaluating, and validating antimicrobial interventions to reduce the presence of potential pathogenic microorganisms.