Pathogenicity and virulence of <i>Shigella sonnei</i> : A highly drug-resistant pathogen of increasing prevalence

Abstract

<i>Shigella</i> spp. are the causative agent of shigellosis (or bacillary dysentery), a diarrhoeal disease characterized for the bacterial invasion of gut epithelial cells. Among the 4 species included in the genus, <i>Shigella flexneri</i> is principally responsible for the disease in the developing world while <i>Shigella sonnei</i> is the main causative agent in high-income countries. Remarkably, as more countries improve their socioeconomic conditions, we observe an increase in the relative prevalence of <i>S. sonnei</i>. To date, the reasons behind this change in aetiology depending on economic growth are not understood. <i>S. flexneri</i> has been widely used as a model to study the pathogenesis of the genus, but as more research data are collected, important discrepancies with <i>S. sonnei</i> have come to light. In comparison to <i>S. flexneri, S. sonnei</i> can be differentiated in numerous aspects; it presents a characteristic O-antigen identical to that of one serogroup of the environmental bacterium <i>Plesiomonas shigelloides</i>, a group 4 capsule, antibacterial mechanisms to outcompete and displace gut commensal bacteria, and a poorer adaptation to an intracellular lifestyle. In addition, the World Health Organization (WHO) have recognized the significant threat posed by antibiotic-resistant strains of <i>S. sonnei</i>, demanding new approaches. This review gathers knowledge on what is known about <i>S. sonnei</i> within the context of other <i>Shigella</i> spp. and aims to open the door for future research on understanding the increasing spread of this pathogen.