The facultative anaerobe group B Streptococcus (GBS) is an opportunistic pathogen of pregnant women, newborns, and the elderly. Although several virulence factors have been identified, environmental factors that regulate the pathogenicity of GBS have not been well characterized. Using the dynamic in vitro attachment and invasion system (DIVAS), we examined the effect of oxygen on the ability of GBS to invade immortalized human epithelial cells. GBS type III strain M781 invaded human epithelial cells of primitive neurons, the cervix, the vagina, and the endometrium in 5- to 400-fold higher numbers when cultured at a cell mass doubling time ( t d ) of 1.8 h than at a slower t d of 11 h. Invasion was optimal when GBS was cultured at a t d of 1.8 h in the presence of ≥5 oxygen and was significantly reduced without oxygen. Moreover, GBS grown in a chemostat under highly invasive conditions ( t d of 1.8 h, with oxygen) was more virulent in neonatal mice than was GBS grown under suboptimal invasion conditions ( t d of 1.8 h, without oxygen), suggesting a positive association between in vitro invasiveness with DIVAS and virulence.
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