Expression of flagella and motility by Shigella

Abstract

Since the discovery of Shigella as the aetiologic agent of acute dysentery almost 100 years ago, this organism has been described as a non-motile and nonflagellated organism that invades the human colonic mucosa. In this study, the production of flagella by prototypic strains of all four Shigella species and, moreover, by fresh clinical isolates was demonstrated by electron microscopy. The flagellum of Shigella (flash) is approximately 10 microns long and 12-14 nm in diameter and is typically seen emanating from one pole of the bacterium. Flash is composed of a putative structural polypeptide subunit of 33-38 kDa that shares immunological similarities with Escherichia coli, Salmonella spp., and Proteus mirabilis flagellins, and with the recently described recombinant Shigella flagellins (FliCSS and FliCSF) expressed in E. coli K-12. A fliCSS-specific oligo probe hybridized with all four Shigella species, while a fliCSF probe hybridized with all Shigella flexneri and Shigella dysenteriae strains, but not with all Shigella sonnei or Shigella boydii strains, indicating genetic divergence among their flagellin genes. Shigella exhibits motility in low-concentration motility agar under physiological growth conditions. The expression of flash and motility appears to be strictly regulated by unidentified genetic and environmental factors. These heretofore undescribed features may allow the bacteria to circumvent the natural intestinal mucosal defences leading to bacterial colonization and disease. The motility of shigellae may represent an evolutionary adaptation important for bacterial survival.

Enteroaggregative Escherichia coli expresses a novel flagellin that causes IL-8 release from intestinal epithelial cells

“…Nevertheless, Girón demonstrated that under carefully controlled conditions, Shigella can in fact be induced to express flagella, but in very low numbers (one flagellum per 300-1,000 organisms), and that they do exhibit some motility in very soft (0.175%) agar (21). The high degree of homology between the flagellin from EAEC 042 and that from S. dysenteriae and S. flexneri raises the intriguing hypothesis that expression of flagellin in vivo may contribute to the severe inflammation characteristic of shigellosis.…”

Cloning and characterization of the region III flagellar operons of the four Shigella subgroups: genetic defects that cause loss of flagella of Shigella boydii and Shigella sonnei

“…Shigellae have been regarded as nonmotile organisms lacking flagella (15), and this characteristic has been used as one of the taxonomic and diagnostic criteria to distinguish shigellae from other enteric bacteria. However, it has been reported that some prototypical strains of the four subgroups and two fresh clinical isolates of S. sonnei are sparsely flagellate (19). We have not yet detected any motile strain among the four subgroups in the more than 20 laboratory strains we have examined so far; instead we have detected defective flagellar genes in some strains of these subgroups (4,56).…”

Breaching the mucosal barrier by stealth: an emerging pathogenic mechanism for enteroadherent bacterial pathogens

“…Similarly, recent studies have suggested that cytolethal distending toxin (24) is a primary stimulus for IL-8 secretion induced by C. jejuni. It is also unclear whether Shigella, which have only recently been shown to produce functional flagella (25), use flagellin as an effector molecule in the recruitment of PMNs.…”