Group B Streptococcus (GBS) is a leading cause of sepsis and meningitis in neonates, an important factor in premature and still births worldwide, and a threat to immunocompromised and elderly adults. The prevention strategy for neonatal invasive disease targets maternal colonization, the primary risk factor, through late-gestational screening and intrapartum antibiotics. This approach has resulted in a significant decline in disease rates; however, this decrease has stagnated in the 2000s, and maternal re-colonization following treatment is common. For my doctoral work, I examined phenotypic and genotypic factors which facilitate colonization, antibiotic tolerance, and persistence of GBS including biofilm production, quorum sensing, and phenotypic heterogeneity. The assessment of biofilm formation across a diverse set of isolates, including colonizing and invasive clinical human strains, found that weak biofilm production correlated with genotype, pilus profile, and invasive disease. Furthermore, asymptomatic colonization was associated with strong biofilm production suggesting a colonization advantage for strong biofilm producers. The role of a putative quorum-sensing auto-inducing peptide, RgfD, was investigated through the creation of a deletion mutant through homologous recombination. In this work, rgfD was found to drive adherence to decidualized human endometrial cells through the upregulation of the regulator of fibrinogen-binding two-component system suggesting quorum-sensing in GBS is important for colonization. Lastly, the importance of phenotypic diversification in a single strain of GBS was assessed through the identification and characterization of a locked mutant small colony variant (SCV) derived from a clinical isolate. This is the first demonstration of SCV formation in GBS. The mutant SCV displayed increased penicillin tolerance and biofilm production, but reduced phagocytic uptake by THP-1 macrophages. Furthermore, the SCV phenotype was inducible when treated with antibiotics or exposed to acidic pH, which, alongside whole transcriptome analysis, suggests variant-formation to be driven by stress response in GBS. The work contained herein furthers the understanding of GBS colonization and identifies key phenotypic and genotypic characteristics driving colonization and persistence that must be considered in the development of future therapeutics.
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