Molecular epidemiology of group B <italic>Streptococcus</italic>: Phenotypic and genotypic characterization.

Group B Streptococcus (GBS) (Streptococcus agalactiae ) causes invasive disease in neonates, young infants, and pregnant women and is an emerging cause of disease in nonpregnant adults, especially those with underlying medical conditions, and the elderly. GBS was initially identified as a problem among neonates and pregnant women, therefore, most epidemiologic studies have focused on perinatal disease. Little is known about the molecular epidemiology of GBS among nonpregnant adults. In this dissertation I describe: (1) the development of a novel GBS capsular typing method as an alternative to conventional serotyping, (2) characterization of the genetic diversity and antibiotic resistance of colonizing GBS isolates from healthy young adults, and (3) the frequency of antimicrobial resistance and capsular type distribution among invasive GBS isolates. Through this research, we determined that genotypic serotype classification of GBS by dot blot capsular typing is a specific and useful alternative to conventional serotyping. Capsular typing, along with molecular subtyping by pulsed-field gel electrophoresis (PFGE), suggested that isolates asymptomatically colonizing nonpregnant adults have a molecular epidemiology similar to that reported in the literature for invasive strains, but with elevated levels of resistance to clindamycin and erythromycin. Comparison of colonizing strains between nonpregnant adults and invasive GBS isolates confirmed that both collections have similar capsular type distributions, however, colonizing strains displayed unexpectedly high levels of clindamycin and erythromycin resistance compared to strains causing invasive disease. We also identified levofloxacin-resistant and cefazolin-intermediate GBS strains among our collections, both which have only recently emerged. GBS characterization will inform the development of antimicrobial treatment protocols and guide formulation of candidate GBS vaccines.Ph.D.Health and Environmental SciencesPublic healthUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/124363/2/3138115.pd