Characterization of Shiga toxin-producing Escherichia coli (STEC) in feces of healthy and diarrheic calves in Urmia region, Iran
Background and Objectives: Shiga toxin-producing Escherichia coli (STEC) have emerged as human pathogens and contamination of foods of animal origin has been a major public health concern. The aim of the present study was to determine the dissemination of STEC in healthy and diarrheic calves in Urmia region which is located in West Azerbaijan province, Iran.
Materials and Methods: In the current study, a total of 124 Escherichia coli isolates from clinically healthy (n=73) and diarrheic calves (51) belonging to 6 different farms located in West Azerbaijan province, Iran, were screened by the polymerase chain reaction (PCR) assay for the presence of virulence genes characteristic for STEC, that is, Shiga-toxin producing gene(s) (stx1, stx2), intimin (eaeA) and enterohaemolysin (hlyA).
Results: STEC strains were recovered from 21.92% (16/73) in healthy calves, and 19.6% (10/51) in diarrheic calves. Overall, PCR results showed that 6 (23.1%) isolates carried stx1 gene, 7 (26.92%) possessed stx2 gene while 13 isolates (50%) gave positive amplicon both for stx1 and stx2 genes. All stx positive strains were assayed further to detect eaeA and hlyA sequences. 7 out of the 26 (26.92%) Shiga toxin gene positive isolates were positive for the eaeA gene, and 15 (57.69%) were positive for the hlyA gene. Both virulence genes (eaeA and hlyA) in the same isolate were observed in 5 (19.23%) of the stx+ isolates. In total, diverse virulence gene profiles were detected, from which strains with the genetic profile stx1 stx2 hlyA was the most prevalent. In addition, eaeA gene was more evident in isolates from diarrheic calves than in healthy calves.
Conclusion: As a result, calves seem to be the group with higher rate of STEC excretion within the herds and aspects of calf management may represent specific control points for reducing STEC spread within dairy units. The results also appear to indicate that STEC E. coli strains are a normal part of intestinal bacterial populations in calves.