Diarrheal is the second most prevalent causes in under five-year old children worldwide. Shigella spp. which renders dysentery in children are mostly prevailed in underdeveloped countries, where hygiene were poor practices. Shiga toxin is responsible for fatal manifestations of shigellosis including dysentery, hemorrhagic colitis, uremic-hemolytic syndrome, etc. By increasing our knowledge on toxin presence in isolates,  effective treatment can be done in future and prevented from further complications. we investigated the frequency of stx1 gene in Shigella spp. (except S. dysenteriae) isolated from diarrheal patients in Ahvaz city, southwestern Iran.
Methods: During a two-year period, 227 Shigella species including 60 S. flexneri, 157 S. sonnei and 10 S. boydii were obtained from diarrheal patients. Upon DNA extraction, PCR was applied for stx1 gene detection in validated isolates.
Findings: Based on our findings, none of the organisms were recognized to be positive regarding the stx1 gene.
Conclusion: The lack of toxin production among the Shigella spp in this area shows that the encoding shiga-toxin phage is not carried by these isolates. However, regarding the emergence of this phage in other territories of the world and the unknown condition for transmission to other species, we can’t make an absolute decision on its absence in this region.

Keywords: Shiga toxin -1, Shigella, Shigella dysenteriae