Genetic features of Streptococcus agalactiae strains causing severe neonatal infections, as revealed by pulsed-field gel electrophoresisand hylB geneanalysis

A collection of 114 independent Streptococcus agalactiae strains, including 54 strains isolated from the cerebrospinal fluid (CSF) samples of neonates and 60 strains from asymptomatic patients, was characterized by pulsed-fie ld gel electrophoresis (PFGE) of DNA restricted with SmaI and by PCR analys is of the hylB gene. All strains mere previously studied by multilocus enzy me electrophoresis (MLEE) (R. Quentin, H. Huet, F.-S. Wang, P. Geslin, A. G oudeau, and R. K. Selander, J. Clin. Microbiol, 33:2576-2581, 1995), Among these 114 strains, there were 92 PFGE patterns. Eleven genetic groups (A to K) were identified with 38% divergence, A more homogeneous group (PFGE gro up A) was defined, consisting of 73% of the strains previously identified a s belonging to a particular MLEE phylogenetic group. A 162-kb fragment was identified as a marker of strains that invaded the central nervous system o f neonates. It was detected in 69% of the PFGE patterns obtained with CSF i solates and in only 1.8% of the PFGE patterns obtained with carrier strains . The hylB gene encoding hyaluronate lyase was amplified for all strains in our collection. Ten of 15 isolates belonging to an MLEE subgroup, previous ly described as being likely to cause invasive infection, had an insertion in the hylB gene (IS1548).