Clonal analysis of Streptococcus agalactiae isolated from infants with neonatal sepsis or meningitis and their mothers and from healthy pregnant women.

The purpose of this study was to evaluate if group B streptococci (GBS) isolated from infants with neonatal sepsis or meningitis and their mothers differ from GBS isolated from healthy pregnant women who gave birth to healthy infants. Danish clinical isolates of GBS (n = 118) were characterized by multilocus enzyme electrophoresis, a method recently used to identify virulent clones of GBS type III from North American infants. By analysis of allelic profiles of 11 metabolic enzyme loci, 43 different electrophoretic types were found. Clustering analysis revealed two primary phylogenetic divisions at a distance of > 0.8, both containing serotype III isolates. One division, comprising virtually all disease isolates, showed a population structure like that of traditional pathogens. The other division, containing the majority of carrier isolates, had a structure reminiscent of that of mucosal commensals, with each isolate being different.