PROJECT SUMMARY
Emergence and evolution of bacterial pathogens in humans is the result of a complex interplay between
bacterial factors and the host immune response. Streptococcus agalactiae (group B Streptococcus, GBS)
emerged in the late 1960s and early 1970s as a frequent cause of sepsis and meningitis in infants <90 days of
age. Twenty years later, GBS was also recognized as a significant cause of disease in adults. Serum cross-
reactivity to the GBS capsular polysaccharide (CPS) led to the recognition of 10 CPS types (Ia/Ib, II-IX). The
epidemiology of infant disease is defined by GBS strains of CPS Ia and III and much research has been
devoted GBS pathogenesis and disease prevention in this age group. In contrast, adult disease is dominated
by strains of CPS type IV and V of which we understand little of the bacterial mechanisms contributing to
disease. Combined with the fact that of the ~30,000 cases of invasive GBS disease that occur annually in the
US two-thirds occur in adults, a major knowledge gap exists in our understanding of adult GBS disease
mechanisms. We previously performed one of the only studies to examine CPS V GBS and discovered that
the majority (>85%) are of a single sequence type (ST), ST1, and evolve by small genetic changes
(mutations). Here, we extend our previous analysis to include CPS V GBS strains isolated at the beginning of
the rise in adult GBS disease. Combined with our previous analysis, our data indicate that “early” (pre-1992)
CPS V GBS disease strains were more likely to be ST2 compared to contemporary CPS V GBS among which
ST1 predominates. In addition, we have identified genes encoding an unstudied two-component gene
regulatory system (TCS) as highly polymorphic within the ST1 population consistent with a critical role in CPS
V GBS pathogenesis. These data form the basis of this proposal which seeks to test the hypothesis that ST1
GBS have altered host-pathogen interaction compared to non-ST1 strains owing to differences in gene content
and global gene regulation. Using RNA-sequencing following exposure to human blood ex vivo and models of
GBS colonization and disease, Specific Aim 1 will determine the contribution of gene regulatory differences
between ST1 and non-ST1 GBS that contribute to differences in host-pathogen interaction and dominance of
ST1 among contemporary CPS V GBS. In Specific Aim 2, we test the hypothesis that the identified TCS
contributes to ST1 phenotypic characteristics and predominance among CPS V GBS. We will generate
isogenic deletion mutants and compare transcriptomes to the parental strains using RNA-sequencing to define
the key regulatory targets of the TCS. Subsequently, we will correlate differences in gene regulation to
differences in host-pathogen interaction using models of GBS colonization and disease. Completion of these
studies will provide critical new information regarding CPS V GBS disease in adults and serve as a model for
investigation of other CPS types. Moreover, the proposed studies are designed to generate key preliminary
data needed for deeper investigations into GBS emergence and pathogenesis in humans.