Detection of shiga toxin producing Escherichia coli isolated from children and cattle using PCR technique

Abstract

This study was undertaken to detect STEC isolates, gene(Stx2) in Escherichia coli isolates
and characterize them by biochemical tests , enterohemolysin production and PCR.During a
period of seven months (November 2007 to May 2008), a total of 280 fecal samples were
collected from 120 hospitalized children suffering from diarrhea and 160 cattle fecal samples .
Feces specimens were screened for the presence of NSF E. coli and STEC by cultured on
sorbitol MacConkey agar (SMAC).A total of 209 (74.6%) non-sorbitol fermenting (NSF)
bacterial isolates were obtained , 69 (57.5%) from children fecal samples and 140 (87.5%) from
cattle feces . Of which 5 (4.16%) NSF E. coli isolated from children fecal samples and 38
(23.75%) from cattle feces. NSF isolates were identified as Shiga toxin producing E. coli
(STEC), but only 16 (10%) isolates of cattle and 2 (1.6%)isolates of children were PCR-positive
for (Stx2) gene which gave amplification bands at 346 bp using DNA marker in the interpretation
of the results. Among 18 STEC studied, a total of 16 (88.8%) isolates expressed enterohemolysin
on washing sheep blood agar plates.On the other hand, the study was showed that the sensitivity
and specificity of PCR technique in diagnosis of STEC were 41.8% , 100% respectively, in
comparison with other tests like biochemical tests, sensitivity and specificity of these tests were
(100% , 86.9%) respectively.