Non‐O157 Shiga Toxin‐producingEscherichia coliIsolated from Diarrhoeic Calves in Argentina

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Abstract
Summary: Faecal samples from 76 diarrhoeic calves belonging to 36 farms located in the Pampas plain, Argentina, were examined for Shiga toxin‐producingEscherichia coli(STEC). A total of 15 STEC strains were isolated from 12 (15.8%) calves which came from six different farms. Allstxpositive strains assayed by PCR were also positives in the Vero cell cytotoxicity test. The majority (60.0%) of the STEC strains carried thestx1gene. Twelve (80.0%) of the STEC isolates which belonged to serotypes O5:H‐ (n = 4), O26:H11 (n = 4), O26:H‐ (n = 1), O111:H‐ (n = 2), and O123:H38 (n = 1) were also enterohaemolysin (EHly) positive and carried the gene encoding for intimin (eae). All thestxpositive strains were negative for thebfpAgene. Localized adherence to HEp‐2 cells were observed in 83.3% of theeae+ STEC strains. STEC belonging to serotype O5:H‐ showed atypical biochemical properties, including urease production. Urease was also produced by two strains belonging to serotypes O153:H? and non‐typeable, respectively. Resistance to three or more antibiotics was observed in 12 (80.0%) of the STEC isolates. Most of the serotypes of STEC recovered in this survey carried virulence traits that are associated with increased human and bovine pathogenicity. The present study shows that highly virulent STEC strains are being shed by diarrhoeic calves from farms located in a high incidence area of human STEC infections.