Characterization of s1289 in Biofilm Formation and Infection in S. flexneri

Abstract

Shigella flexneri is an intracellular pathogen that invades colonic epithelial cells and causes bacterial dysentery, which accounts for approximately 165 million cases worldwide and 1 million associated deaths, annually. Shigella infections are predominant in third world countries with poor access to hygiene resources. It can be spread via person to person contact or by contaminated food or water. What is known about Shigella pathogenesis is that it can withstand the acidic environments of the digestive tract, evade immune responses, invade intestinal epithelium using a Type 3 Secretion System (T3SS) and acquire actin‐based motility by manipulating the host cell actin cytoskeleton. Another characteristic of the pathogen is its ability to disseminate between epithelial cells via the formation of plasma membrane protrusions that resolve into vacuole like protrusions (VLP's) and finally collapse and form a vacuole in the adjacent intestinal cell. Although much is known about how the pathogen invades and spreads into neighboring intestinal cells using the T3SS, there is not enough information on how Shigella transit through the intestinal tract and what events occur prior to infection of colonic cells. We decided to focus on the possibility of other extracellular components in the bacterium that could contribute to virulence. The gene s1289 in Shigella chromosomal DNA encodes for an outer membrane autotransporter protein that can possibly be linked with adhesion to host cells and may contribute to invasion. Recent research has shown that the presence of bile salts induces biofilm formation of S. flexneri. Formation of biofilm is an important determinant for increased adherence and virulence in E. coli strains, but has not been thoroughly investigated in S. flexneri. We decided to test the role of gene s1289 in the formation of S. flexneri biofilms and in adherence to intestinal cells. Our hypothesis was that if we were able to delete the gene s1289 from the bacterial genome, the new mutant strain would lose its capacity to form biofilms and to adhere to colonic epithelial cells. We created a construct displaying a disrupted version of s1289 in E. coli and introduced it in S. flexneri by conjugation. After allelic exchange by homologous recombination, we identified mutant strains displaying the disrupted version of s1289 in their genome. We determined biofilm thickness using confocal microscopy, tested for susceptibility of biofilm using antimicrobial agents, and investigated the ability of the mutant to infect HT‐29 intestinal cells. Although the Δs1289 mutant did form biofilm in presence of 0.4% bile salts, results showed that the structure of the biofilm exhibited reduced thickness compared to wild type. Preliminary infection results indicate a possible adhesion defect in mutant bacteria, therefore reducing invasion in colon cells. However, wild type and mutant biofilms demonstrated no difference in susceptibility to antimicrobials. We conclude that the S1289 protein potentially contributes to biofilm formation and adherence of S. flexneri to HT‐29 cells.Support or Funding InformationUPR‐PRISE Program. Funded by NIH‐NIGMS #2R25GM096955This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.