Pathogenicity and virulence of Shigella sonnei : A highly drug-resistant pathogen of increasing prevalence

Abstract

Shigella 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, Shigella flexneri is principally responsible for the disease in the developing world while Shigella sonnei 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 S. sonnei . To date, the reasons behind this change in aetiology depending on economic growth are not understood. S. flexneri has been widely used as a model to study the pathogenesis of the genus, but as more research data are collected, important discrepancies with S. sonnei have come to light. In comparison to S. flexneri, S. sonnei can be differentiated in numerous aspects; it presents a characteristic O-antigen identical to that of one serogroup of the environmental bacterium Plesiomonas shigelloides , 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 S. sonnei , demanding new approaches. This review gathers knowledge on what is known about S. sonnei within the context of other Shigella spp. and aims to open the door for future research on understanding the increasing spread of this pathogen.

Twenty-five years of sentinel laboratory-based surveillance of shigellosis in a high-income country endemic for the disease, Israel, 1998 to 2022

“…The secular trend of increase of S. sonnei relative weight in the aetiology of culture-confirmed shigellosis in Israel was driven by a decline in S. flexneri shigellosis incidence and is in line with a similar trend in countries undergoing economic development and improvements in sanitation and water quality [ 6 , 23 ]. It probably reflects the better adaptation of S. sonnei than S. flexneri to more restricted modes of transmission associated with specific S. sonnei determinants such as a unique O antigen, the presence of a capsule, a mechanism to displace other enteric bacteria, which all act in protection against environmental stresses [ 24 ].…”

Shigella sonnei utilises colicins during inter-bacterial competition

“…Whilst there are a number of differences between S. sonnei and S. flexneri [16], in the context of anti-bacterial activity, one of the key distinctions is the presence of a Type VI Secretion System (T6SS). A T6SS has been identified in S. sonnei but only remnants remain in S. flexneri (16).…”

“…Whilst there are a number of differences between S. sonnei and S. flexneri [16], in the context of anti-bacterial activity, one of the key distinctions is the presence of a Type VI Secretion System (T6SS). A T6SS has been identified in S. sonnei but only remnants remain in S. flexneri (16). In one clinical isolate it has been demonstrated that this T6SS plays a key role in outcompeting S. flexneri during infection or in polymicrobial environments thus allowing S. sonnei to gain a competitive advantage [17].…”