RESULTS:

Group B streptococcus (GBS) is a chain-forming commensal bacterium and opportunistic pathogen that resides in the gastrointestinal and genitourinary tract of healthy adults. GBS can cause various infections and related complications in pregnant and nonpregnant women adults and newborns. Investigations of the mechanisms by which GBS causes disease pathogenesis often utilize colony count assays to estimate bacterial population size in experimental models. In other streptococci such as group A streptococcus and pneumococcus variation in the chain length of the bacteria that can occur naturally or due to mutation can affect facets of pathogenesis such as adherence to or colonization of a host. No studies have reported a relationship between GBS chain length and pathogenicity. Here we used GBS strain 874391 and several derivative strains displaying longer chain-forming phenotypes (874391pgapC 874391ΔcovR 874391Δstp1) to assess the impact of chain length on bacterial population estimates based on the colony-forming unit (c.f.u.) assay. Disruption of GBS chains via bead beating or sonication in conjunction with fluorescence microscopy was used to compare chaining phenotypes pre- and post-disruption to detect long- and short-chain forms respectively. We used a murine model of GBS colonization of the female reproductive tract to assess whether chaining may affect bacterial colonization dynamics in the host during chronic infection in vivo. Overall we found that GBS exhibiting long-chain form can significantly affect population size estimates based on the colony count assay. Additionally we found that the length of chaining of GBS can affect virulence in the reproductive tract colonization model. Collectively these findings have implications for studies of GBS that utilize colony count assays to measure GBS populations and establish that chain length can affect infection dynamics and disease pathogenesis for this important opportunistic pathogen.