Group B Streptococcus CovR regulation modulates host immune signalling pathways to promote vaginal colonization

Abstract

Summary Streptococcus agalactiae (Group B Streptococcus, GBS) is a frequent commensal organism of the vaginal tract of healthy women. However, GBS can transition to a pathogen in susceptible hosts, but host and microbial factors that contribute to this conversion are not well understood. GBS CovR/S (CsrR/S) is a two component regulatory system that regulates key virulence elements including adherence and toxin production. We performed global transcription profiling of human vaginal epithelial cells exposed to WT, CovR deficient, and toxin deficient strains, and observed that insufficient regulation by CovR and subsequent increased toxin production results in a drastic increase in host inflammatory responses, particularly in cytokine signaling pathways promoted by IL-8 and CXCL2. Additionally, we observed that CovR regulation impacts epithelial cell attachment and intracellular invasion. In our mouse model of GBS vaginal colonization, we further demonstrated that CovR regulation promotes vaginal persistence, as infection with a CovR deficient strain resulted in a heightened host immune response as measured by cytokine production and neutrophil activation. Using CXCr2 KO mice, we determined that this immune alteration occurs, at least in part, via signaling through the CXCL2 receptor. Taken together, we conclude that CovR is an important regulator of GBS vaginal colonization and loss of this regulatory function may contribute to the inflammatory havoc seen during the course of infection.

Streptococcus salivarius K12 Limits Group B Streptococcus Vaginal Colonization

“…3A). In mice colonized with A909, we observed rates of bacterial load and persistence similar to those seen previously (14). Additionally, the amount of K12 recovered from the vaginal vault was 10-fold lower than what was recovered for GBS (Fig.…”

“…To assess immune induction, we quantified the secretion of the neutrophil chemokine IL-8 from human vaginal epithelial cells following incubation with GBS, K12, or both strains together. As seen previously, GBS was a potent inducer of IL-8 secretion from vaginal cells (14), yet K12, either with or without the pSsal-K12 plasmid, did not induce IL-8 production over levels in medium controls (Fig. 2D).…”

“…All animal work was approved by the Office of Lab Animal Care at San Diego State University and conducted using accepted veterinary standards. Eight-to 12-week-old female CD1 mice (Charles River Laboratories, Wilmington, MA) were injected intraperitoneally with 0.5 mg 17␤-estradiol (Sigma-Aldrich, St. Louis, MO) in 100 l sesame oil on day Ϫ1 (13,14). For single-challenge experiments, on day 0, mice were vaginally inoculated with 1 ϫ 10 7 CFU of strain A909 or K12.…”

“…To substantiate our in vitro findings that K12 is capable of interacting with the human vaginal epithelium, we assessed the ability of K12 to colonize the vaginal tract in vivo. Using our previously established model of murine GBS vaginal colonization (13,14), we monitored the bacterial levels of mice colonized with a single inoculation of either GBS A909 or K12 over time. We detected vaginal colonization with K12 in 100% of mice 1 day postinoculation, and on subsequent days, mice began clearing the bacteria, with approximately half of the animals clearing K12 by 3 days postinoculation (Fig.…”

The Sensor Histidine Kinase RgfC Affects Group B Streptococcal Virulence Factor Expression Independent of Its Response Regulator RgfA

“…Like other prokaryotic organisms, signaling in GBS is achieved primarily by two-component signaling systems (TCS) that regulate gene expression in response to external signals (1,3,4). The GBS genome sequence indicates the presence of 18 to 20 TCS (9), and the roles of a few TCS have been well characterized and include CovR/CovS (10)(11)(12)(13)(14)(15), DltR/DltS (16), CiaH/CiaR (17), SAK_0188/0189 (18), RgfC/A (19,20), and FpsR/S (21). Previous studies have indicated that GBS deficient for RgfC/A exhibit reduced adherence to extracellular matrix components due to altered expression of the fibrinogen binding proteins, such as FbsA and FbsB (19,20).…”