In this study 127 out of 262 fecal swabs collected from newly born diarrheic Frisian calves harboured Escherichia coli with an incidence of 48.47% non O157 and 10.30% were O157. Serological testing showed that the most predominant serovars were O1, O8, O25, O26, O55, O86, O125, O126, O146, O151 and 2 isolates were untypable as well as O157:H7 negative.
All bacterial isolates showed growth after various treatments tested for biochemical and hemolytic activity and showed no changes. Studying the virulence factors revealed that 80% of E. coli isolates non O157 and 33.3% of isolates of O157 were hemolytic.
Using PCR to detect the presence of Sta gene in four groups (first group contains 12 serotyped isolates, second group contains 5 non serotyped isolates but showing typical biochemical activity like E. coli, third group contains 5 non serotyped isolates and showing different biochemical activity from E. coli and the fourth group constitutes all the previous isolates but being cultured directly from feces upon broth for 7 hrs, as well as the serotyped O157 isolates. The results revealed that 9 (75%) out of 12 serotyped isolates (in the 1st group), 4 (80%) out of 5 isolates (in the 2nd group), 3 (60%) out of 5 (in the 3rd group) showed similar results to the 4th group after 7 hrs growth in broth from direct fecal samples.
The infant mouse assay was used to confirm the production of (Sta) toxin in the PCR positive isolates. We found that all the isolates showed positive result with PCR were questionably positive with infant mouse assay.
Using Multiplex PCR to detect the presence of SLT2 and eaeA genes in the O157 isolates revealed negative results which confirmed by Vero cell assay.
From the present study we concluded that Escherichia coli are persistently associated with newly born diarrheic calves, especially the enterotoxigenic type (producing heat stable toxin) which can be detected directly using PCR from the fecal samples. |
