Evaluation of Shigella flexneri Biofilm Formation and Its Effect on the Expression of Toxin-antitoxin Genes

 Shigella flexneri is a highly contagious Gram-negative bacterium that causes severe diarrhea, especially in children under ten years old. The biofilm formation in this species increases its resistance to antibiotics. Given the important role of toxin-antitoxin (TA) systems in the stability and survival of bacteria under stress condition, this study was aimed to evaluate the expression of genes encoding TA systems and Lon protease (lonp) as the main protein regulating the expression and function of these systems in this microorganism in terms of biofilm formation.

 In this study, the standard Shigella flexneri ATCC 12022 was used. After the bacteria culture on the specific culture medium, the ability to form biofilm was quantitatively evaluated by microtiter plate method. Then, the expression level of the mentioned genes was assessed compared to the control group using real-time PCR.

 The results of microtiter plate test showed that the studied Shigella flexneri was a strong biofilm strain. The qPCR results showed an increase in gene expression of the studied toxins and Lon protease at 8 and 24 h following biofilm formation induction (P<0.01).

 Due to the significant increase in the expression of the studied genes, especially Lon protease, GNAT and maz toxins at 24 h after biofilm formation, they can be potentially used as antimicrobial targets in new studies.