Production and Composition of Group B Streptococcal Membrane Vesicles Vary Across Diverse Lineages

Abstract

Although the neonatal and fetal pathogen Group B Streptococcus (GBS) asymptomatically colonizes the vaginal tract of ∼30% of pregnant women, only a fraction of their offspring develops invasive disease. We and others have postulated that these dimorphic clinical phenotypes are driven by strain variability; however, the bacterial factors that promote these divergent clinical phenotypes remain unclear. It was previously shown that GBS produces membrane vesicles (MVs) that contain active virulence factors capable of inducing adverse pregnancy outcomes. Because the relationship between strain variation and vesicle composition or production is unknown, we sought to quantify MV production and examine the protein composition, using label-free proteomics on MVs produced by diverse clinical GBS strains representing three phylogenetically distinct lineages. We found that MV production varied across strains, with certain strains displaying nearly twofold increases in production relative to others. Hierarchical clustering and principal component analysis of the proteomes revealed that MV composition is lineage-dependent but independent of clinical phenotype. Multiple proteins that contribute to virulence or immunomodulation, including hyaluronidase, C5a peptidase, and sialidases, were differentially abundant in MVs, and were partially responsible for this divergence. Together, these data indicate that production and composition of GBS MVs vary in a strain-dependent manner, suggesting that MVs have lineage-specific functions relating to virulence. Such differences may contribute to variation in clinical phenotypes observed among individuals infected with GBS strains representing distinct lineages.

Group B streptococcal membrane vesicles induce proinflammatory cytokine production and are sensed in an NLRP3 inflammasome-dependent mechanism in human macrophages

“…MVs were quantified via nanoparticle tracking analysis using a NanoSight NS300 (Malvern Panalytical Westborough, MA, USA) equipped with an automated syringe sampler as described previously (22, 33, 34). For each sample, MVs were diluted in PBS (1:100 – 1:1000) and injected with a flow rate of 50.…”

“…MVs were isolated as previously described (22). Briefly, overnight THB cultures were diluted 1:50 into fresh broth and grown to late logarithmic phase (optical density (OD) 600 = 0.9).…”

“…In support of this finding, GBS MVs were shown to induce production of the neutrophil chemokine CXCL1 in a murine model of in utero infection (17, 19), which has been shown in other GBS infection models (20, 21). Further, we recently reported that GBS MV production varies in abundance and protein composition across STs (17, 19, 22). More specifically, several immunomodulatory virulence factors, including hyaluronidase, C5a peptidase, and sialidase were highly and differentially abundant across STs (22).…”

“…Further, we recently reported that GBS MV production varies in abundance and protein composition across STs (17, 19, 22). More specifically, several immunomodulatory virulence factors, including hyaluronidase, C5a peptidase, and sialidase were highly and differentially abundant across STs (22). Together these data indicate that MVs promote proinflammatory immune responses; however, no prior studies have comprehensively examined the mechanisms by which human leukocytes respond to GBS MVs.…”

Bacterial and Host Determinants of Group B Streptococcal Infection of the Neonate and Infant

“…Hemolytic MVs have also been shown to inhibit the activity of reactive oxygen species (ROS), suggesting that GBS may resist neutrophil oxidative killing by quenching ROS ( Armistead et al, 2021 ). MVs composition and abundance are demonstrated to vary based on serotype and lineage indicating differential impact on promoting virulence and systemic infection ( McCutcheon et al, 2021 ). In addition to MVs, other GBS virulence factors may also contribute to lung injury and blood vessel invasion.…”