YfiB: An Outer Membrane Protein Involved in the Virulence of Shigella flexneri

The intracellular pathogen Shigella flexneri, which is the causative agent of bacillary dysentery, significantly influences the worldwide implication of diarrheal infections, consequentially causing about 1.1 million deaths each year. Due to a non-availability of an authorized vaccine and the upsurge of multidrug resistance amongst Shigella strains, there has been a huge demand for further genetic analyses which could help in the advancement of new/improved drugs, and finding vaccine candidates against the pathogen. Whilst many features about the invasion of colonic cells by Shigella have been identified, fundamental gaps in information concerning in what way the bacteria transit, survive, and control gene expression, remain. The present study aims to illustrate the role of yfiB gene in Shigella virulence, which is a part of the periplasmic YfiBNR tripartite signaling system. This system is involved in the regulation of cyclic-di-GMP levels inside the bacterial cells, which is a vital messenger molecule impacting varied cellular processes such as biofilm formation, cytotoxicity, motility, synthesis of exopolysaccharide, and other virulence mechanisms like adhesion and invasion of the bacteria. Through a combination of genetic, biochemical, and virulence assays, we show how knocking out the yfiB gene can disrupt the entire YfiBNR system and affect biofilm formation, bacterial invasion, host-surface attachment, and the overall virulence of Shigella. This study eventually improves our understanding of the in-vivo persistence and survival of Shigella, brings light to the c-di-GMP lead regulation of Shigella virulence, and provides a prospective new target to design anti-infective drugs and vaccines against S. flexneri and other bacterial pathogens.