Shiga toxin-producing Escherichia coli O157:H7 isolated from cattle feedlot effluents

TANARO JD; PIAGGIO MC; GALLI L; GASPAROVIC AMC; ZOLEZZI G; RIVAS M

Amsterdam

Simposio; 8th International Symposium on Shiga toxin (Verocytotoxin) producing Escherichia coli Infections; 2012

Major outbreaks due to the consumption of raw fruits and vegetables or accidental ingestion of water contaminated by Shiga toxin-producing Escherichia coli (STEC) have been increasingly reported. Fresh produces may have been contaminated by direct spreading of cattle manure on growing crops or indirectly via contaminated irrigation. STEC O157:H7 has been shown to survive for long periods in water-trough sediments, and troughs can serve as a reservoir for infection. The research was intended to study the prevalence of STEC O157:H7 in water samples of cattle feedlot effluents in Entre Rios Province, Argentina. Between April 2009 and July 2011, 320 water samples of cattle feedlot effluents in 10 farmers were studied. Two-liter samples were kept for 24 h at room temperature in bottles with Moore swabs. Swabs were incubated in tryticase soy broth (TSB) for 5 h, and then exposed to an acid shock (pH 4.0) for 30 min before neutralization with TSB-Tris (pH 8.7) and incubation at 42C for 24 h. Immunomagnetic separation for E. coli O157 was performed and the immunoconcentrate was streaked onto sorbitol MacConkey agar, O157:H7 ID and Chromagar O157. After incubation at 37C for 24 h, the confluent growth zone and individual colonies were screened for stx1, stx2 and rfbO157 genes by a multiplex PCR. STEC isolates were characterized by biochemical tests, serotyping, stx-genotyping, and by pulsed-field gel electrophoresis (PFGE) using the 24-h PulseNet standardized protocol. Results: By PCR, 43 (13.4%) water samples were rfbO157-stx-positive and 38 (11.9%) STEC O157 strains were isolated. In addition, 172 (53.8%) samples were rfbO157-positive and 76 E. coli O157 strains were recovered. STEC O157 strains were recovered from wastewater feedlot (19/129, 14.7%), waste stabilization ponds (11/130, 8.5%), and watercourses or lagoons near feedlot (8/61, 13.1%). The most prevalent stx-genotype was stx2/stx2c(vh-a) (50%) followed by stx2 (47.4%). All STEC strains harbored the eae, ehxA, and fliCH7 genes. The clonal relatedness of 38 STEC O157 strains was established by XbaI-PFGE. The analysis showed 16 different patterns with 83.9% similarity, with 29 strains grouped in seven clusters (I to VII) of 2?10 strains each one and 100% homology. Unique patterns were observed for nine strains. Some XbaI-PFGE patterns identified are included in the Argentine Database of E. coli O157, corresponding to strains isolated from HUS and diarrhea cases, food, and animals. Among them, AREXHX01.0022 is the second prevalent pattern, representing 5.5% of the total. Control strategies must be considered on cattle farms, in order to limit entry of STEC into the environment. As O157 is not a highly competitive microorganism in aquatic environments, waste stabilization ponds would be useful for minimize its spreading, but this strategy is insufficient.