Abstract
Background: Shiga toxin (Stx) producing Escherichia coli (STEC) colonize human intestinal tract and their infections have asymptomatic clinical manifestations which cause local and systemic pathological changes.
 Objectives: This study intended to establish the role of Shiga toxin (Stx2d) in developing clinical manifestations in STEC infections using experimental models.
 Methods: A total 300 stool samples were screened from hospitalised diarrhoeal patients enrolled in 2% surveillance system at International Centre for Diarrhoeal Disease Research, Bangladesh (icddr,b). The stx gene profile including their variants was identified byPCR.stx2d gene positive STEC PT187 was selected for toxin (s) preparation.Toxin was prepared by centrifugation of culture supernatant. Enterotoxicand paralytic-lethal activities were tested in rabbit ileal loops and mice, respectively. Histopathological study of the rabbit ileal loop segments and different tissues of mice by paraffin embedded method and stained by H & E staining. Cytotoxic effect was performed on HeLa cells.
 Results: Nine STEC strains were identified for stx2 gene positive. Among them STEC PT187 was found stx2d gene positive strain and selected for toxic activities. Toxin (s) responsible for causing accumulation of fluid in rabbit ileal loops and its segments showed inflammation and enterocytenecrosis. In mouse model, toxin(s) was found to cause hind limbs paralysis and death. Brain, spinal cord and kidney tissue of mice showed histopathological changes. Toxin (s) also showed positive cytotoxic activity in HeLa cell.
 Conclusion: In this study, results indicated that Stx2d producing E. coli exhibit not only enterotoxic activity, but also cause impaired neurological functions and cytotoxic effect.
 Bangladesh Med Res Counc Bull 2020; 46(1): 41-47
Highlights
Shiga toxin producing Escherichia coli (STEC) strains have emerged as one of the majorcause of human gastrointestinal diseases resulting in lifethreatening complications such as haemolyticuremic syndrome (HUS) which is the most common cause of acute renal failure in children
Conclusion:In this study, results indicated that Stx2d producing E. coli exhibit enterotoxic activity, and cause impaired neurological functions and cytotoxic effect
Isolation and identification of STEC strainsby PCR: Nine strainsout of 300 stoolsamples were identifiedfor STEC specific genestx[2]
Summary
Shiga toxin producing Escherichia coli (STEC) strains have emerged as one of the majorcause of human gastrointestinal diseases resulting in lifethreatening complications such as haemolyticuremic syndrome (HUS) which is the most common cause of acute renal failure in children. Ahsan CR et al analysis of the stx[1] and stx[2] genes revealed the existence of different variants in both groups. Three stx[1] subtypes (stx[1], stx1c, stx1d) and several stx[2] variants (e.g. stx2c, stx2d, stx2e, stx2f, stx2g) have been described.[4,5,6,7]. Shiga toxin (Stx) producing Escherichia coli (STEC) colonise human intestinal tract and their infections have asymptomatic clinical manifestations which cause local and systemic pathological changes
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