Prevalence and characterization of Shiga toxin-producing Escherichia coli O157:H7/NM in commercial beef abattoirs of Argentina.

MASANA M., LEOTTA G.A., DEL CASTILLO L., D’ASTEK B., PALLADINO M., GALLI L., VILACOBA E., CARBONARI C., TEITELBAUM D., RIVAS M.

Buenos Aires

Simposio; 7th International Symposium on Shiga Toxin (Verocytotoxin) - Producing Escherichia coli infections.; 2009

In Argentina, the information on the prevalence of Shiga toxin-producing Escherichia coli (STEC) O157 in the beef chain has been scarce, and non-systematic. Therefore, the aim of this study was to determine the prevalence of STEC O157:H7/NM under the current commercial operation of national abattoirs. This goal was achieved by sampling for STEC O157 the bovine fecal content of cattle at the abattoir, and the carcasses produced. Six animals from a lot of 30-60 bovines of identified origin were sampled in each visit to an abattoir in such a way to obtain fecal and carcass samples from the same animal. Fecal samples (FS) were collected from the descendent colon near to the rectum, while carcasses samples were obtained by swabbing the carcass surface (CS) with a humidified sponge according to USDA. Enrichment procedures were conducted as follows: 10 g of the feces were incubated in 90 ml of GN Hajna (Difco, USA) at 37ºC for 5 h; for carcass sponges incubation took place in 90 ml of mEC for 2 h at 37ºC. After the primary enrichment, noboviocin was added up to 20 µg/ml and the enrichment broths were further incubated for 18 h at 37ºC. Enriched samples (1 ml) were then processed by immunomagnetic separation (IMS) according to a modification of the USDA/FSIS procedure for STEC O157:H7/NM isolation from foods. Confluent growth zone and colony pools were screened for stx1, stx2 and rfbO157 genes by a multiplex polymerase chain reaction. At least 20 colonies per PCR-positive sample were performed for confirmation. Isolates were characterized by biochemical tests, and the genetic profile (stx1, stx2, ehxA, eae, rfbO157), and H7 flagellar antigen (fliCH7) was established by PCR. Between November 2006 and April 2008, 1622 samples (811 CS, 811 FS) were collected in nine abattoirs from Argentina. These abattoirs, all working under HACCP, contribute with approximately the 18% of the animals slaughtered per year. Bovines were typified as steers (46%), young steers (17%), cows (24%), calves (6%), and heifers (7%), and originated from 9 provinces, being Buenos Aires the biggest supplier (43%). STEC O157 was isolated from 49 samples (3.0%), 20 from CS (2.5 %) and 29 of FS (3.6 %). The carriage of STEC O157 in FS varied in the different types of cattle: steers (3.2%), young steers (4.4%), cows (1.5%), calves (6.4%), and heifers (8.8%). The contamination of carcasses also varied between abattoirs from 0% to 11.1%. In the biochemical characterization all STEC O157 isolates were sorbitol and β-glucoronidase-negative, while toxicity on Vero cells was also demonstrated for all isolates. The prevalent genotype was stx2/stx2c (vh-a) /eae/ehxA/fliCH7 (23/49, 47%), while stx1/stx2 genes were carried out by 8 strains. These results are important as in Argentina the genotype stx2/stx2c (vh-a) is also prevalent in more than 90% of O157-HUS cases. The cattle tested in this work is representative of the common grass feeding production systems, and that the degree of carriage of STEC O157 in cattle is comparable to other international reports.