Light shed on genetic diversity among group B streptococcal isolates

Fluegge K. Pediatr Infect Dis J. 2011; [published online ahead of print July 19].

Invasive group B streptococcal strains comprised a small proportion of noninvasive isolates, suggesting that more virulent strains are selected during invasion, according to recent study results.

Researchers from Germany used pulsed-field gel electrophoresis and surface protein gene profiling to compare invasive neonatal group B streptococcal isolates with noninvasive isolates from newborns who were suspected of having sepsis, but who had sterile blood cultures. Multilocus sequence typing was performed on both kinds of isolates of the most frequent invasive serotype 3, according to the results.

A more diverse fingerprinting pattern was observed in noninvasive isolates than in invasive isolates, and clustering was observed in the invasive strains but not in the noninvasive strains.

Results of the surface protein gene profile indicated significant differences in distribution patterns between noninvasive and invasive isolates.

The most common invasive strain was ST-17, at 68.6%, and the most common noninvasive strain was ST-389 (clonal complex-19), at 47.8%, according to multilocus sequence typing of invasive and noninvasive serotype 3 isolates.

The aim of the study was to investigate the pathogenesis of neonatal group B streptococcal sepsis by illuminating clonal relatedness and diversity among invasive and noninvasive group B streptococcal isolates.

“Our results illustrate a large molecular diversity among neonatal noninvasive [group B streptococcal] strains,” the researchers wrote. “Invasive strains, however, represent only a small proportion of the noninvasive [group B streptococcal] population. These findings suggest a selection process that prefers more virulent strains during invasion.”

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