Virulence-associated genes and toxin-antitoxin system genes of Shigella flexneri: Presence and expression in normal and thermal stress conditions

Background: Acute diarrhea is a major public health concern, especially in developing countries. Some research literature demonstrates that toxin-antitoxin systems (TAs) have a regulatory role in different cellular activities. Therefore, the aim of current study is to evaluate the association between the type II TA systems and the virulence/pathogenesis of S. flexneri strains. Methods: Forty S. flexneri strains were identified by phenotypical and molecular methods from patients with Shigellosis at the Infectious and Tropical Diseases Research Center, Ahvaz, Iran. Then, the occurrence of the toxin-antitoxin system genes (mazEF and relBE) and virulence-associated genes (ipaB, set1A, and virF) was detected by PCR-based sequencing assay. Finally, the expression of these genes was characterized in normal and stress conditions (increased temperature) using the Real Time-qPCR assay. Results: The occurrence of ipaB, set1A, and virF genes was 67.5 , 95, and 92.5 respectively. In addition, all strains were positive for mazEF and relBE genes. The Real time-qPCR assay revealed that expression of ipaB and virF in thermal stress was higher than its expression in normal condition. The same was observed for relBE. Conclusions: A possible association was found between mazF and relE expression increase and ipaB and virF expression increase. However, further investigation is required to elucidate the exact association of these genes