Prevalence and characterization of non-O157 Shiga toxin-producing Escherichia coli recovered from feces and carcasses in commercial beef cattle processing plants in Argentina.

LEOTTA G.A., MASANA M., DEL CASTILLO L., IRINO K., D¡¯ASTEK B., PALLADINO M., GALLI L., CARBONARI C., MILIWEBSKY E., VILACOBA E., RIVAS M.

Buenos Aires

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

A large number of Shiga toxin-producing Escherichia coli (STEC) strains have caused major outbreaks and sporadic cases of human illnesses. Beef cattle are considered reservoir of STEC and can pose significant health risks to humans. The aim of this work was to establish the prevalence of non-O157 STEC on feces and carcass samples in nine abattoirs from Argentina, and to phenotypically and genotypically characterize the isolates. Between November 2006 and April 2008, 811 animals were analyzed, including 6 animals from 135 lots of 30-60 bovines. Fecal samples (FS) were collected from the descendent colon near the rectum, while carcass samples were obtained by swabbing the carcass surface (CS) with a humidified sponge according to USDA. FS were directly plated onto MacConkey agar and incubated at 37¡ÆC for 18 h. For carcass sponges, incubation took place in 90 ml of mEC at 37¨¬C for 2 h. After primary enrichment, 10 ml were added to 90 ml of MacConkey broth and incubated at 37¨¬C for 18 h. Enriched samples were then screened for stx genes by MK-PCR. Each positive sample was plated on MacConkey agar and EMB-Levine agar and incubated at 37¨¬C for 18 h. Confluent growth zone and colony pools of FS and CS were screened for stx1, stx2 and rfbO157 genes by multiplex PCR. Isolates were phenotypically and genotypically characterized. One hundred and six (78.5%) FS, and 62 (46%) CS of 135 single-source cattle lots surveyed included at least one sample containing non-O157 STEC strains. Of 811 animals sampled, 284 (35%) FS and 137 (17%) CS were found to harbour stx genes by PCR screening. A total of 307 non-O157 STEC isolates were recovered. In the biochemical characterization, 96% of isolates were sorbitol-positive, and 89.6% were ¥â-glucoronidase-positive. Toxicity on Vero cells was demonstrated for all isolates. Among 307 non-O157 STEC isolates, 218 isolates were associated with 28 O serogroups (O2, O7, O8, O15, O22, O39, O46, O73, O74, O79, O82, O91, O103, O107, O113, O116, O130, O136, O139, O141, O145, O153, O158, O163, O165, O174, O178, O179) and 89 were considered non-typable (NT). Eighteen H antigens (H2, H7, H8, H11, H12, H14, H16, H18, H19, H21, H25, H27, H28, H38, H42, H45, H46, H49) were distributed in 273 isolates, whereas 31 were non-mobile (H-) and 3 NT. The serotypes that had previously been associated with human disease accounted for 82 (26.7%) of 307 isolates. The frequency of stx genotypes was 28.3% stx2, 17.6% stx1/stx2, 17.6% stx2d (vh-b), 9.4% stx1, 7.2% stx2c (vh-a), 5.2% stx1/stx2d (vh-b), 4.9% stx1/stx2/stx2d (vh-b), 4.2% stx2/stx2d (vh-b), 1.9% stx2-Ox3a, 1.6% stx2NT, 1.3% stx2/stx2c (vh-a), and 0.6% stx2c (vh-a)/stx2d (vh-b). In Argentina, the most prevalent stx genotype in non-O157 HUS cases is stx2. Twenty two (7.2%) isolates carried the eae gene, 152 (49.5%) carried the saa gene, and 182 (59.3%) carried the ehxA gene. This work provides new data for the understanding of the ecology of STEC in commercial beef cattle processing plants and reinforces the importance of cattle as a reservoir of STEC non-O157 strains in Argentina.