Presence of Shiga Toxin Gene in Clinical Iso-lates of Shigella Species from the Past to Present in Bushehr, Iran

The Shiga cytotoxin (Stx) is involved in serious human intestinal diseases. Recently stx has been found in non-S dysenteriae1 Shigella species. This study aimed to identify stx gene in clinical strains of Shigella isolated from two shigellosis outbreaks in previous years in Bushehr, southwest of Iran.
Purified DNA of 143 Shigella isolates was used for PCR to detect stx and ipaH genes. The number of PCR products in various Shigella species isolates was sequenced with the same primers (evt) used to amplify this region.
Fourteen (22.3%) out of 63 shigella isolates related to previous shigellosis outbreaks during 2002-2004 contained the PCR positive result with evt primers. The sequencing results indicated that the evt PCR product had the most identity (97%) with Shigella dysentery shiga toxin subunit A. All clinical shigella strains isolated during 2013-2015 yielded PCR negative results with primers stx and evt. PCR results revealed that ipaH was present in all isolates. According to biochemical and species-specific antiserum tests, the stx gene harboring isolates included 9 (14.3%) S. flexneri, 4 (6.4%) S. sonnei, and 1(1.6%) S. boydii.
The stx gene has already been distributed in different Shigella species of Bushehr region. However, the absence of this gene in the clinical isolates of recent shigellosis outbreaks may be temporary. Because stx gene increases the pathogenic potential of Shigella, it is necessary to monitor the prevalence of the stx harboring Shigella species by molecular methods in the future