Typing ofStreptococcus agalactiae (Lancefield group B)

Abstract

A two-stage typing scheme in routine use in this laboratory is described. The strains of group B streptococci (GBS) are first serotyped and then, if necessary, phage-typing is performed. Serotyping lacks discrimination because almost 40% of strains handled carry either the Ia/c or III/R antigens. On the other hand, the typability rate with phages is less than 80%. The evidence from the combined scheme is consistent with the view that GBS infections occurring within the first five days of life are, with few exceptions, due to acquisition of the mother's flora. After this time the infecting strain may come from other sources. Human and bovine strains of GBS belong predominantly to two recognizably different populations that can be distinguished by antigenic and biochemical differences. There are no patterns of lysis by phages characteristic of either human or bovine strains.

Identification of the High-Virulence Clone of Group B Streptococci by Using a Probe Containing a Putative Aldolase Gene

“…A number of molecular methods have been used for subtyping GBS isolates and correlating particular genotypes with disease [3,4,8,9,13,18]. Studies using restriction endonuclease analysis of chromosomal DNA and ribotyping [3,6,19] and multi-locus enzyme electrophoresis [13,18] have demonstrated the existence of differences in virulence among clones, a phylogenetic dichotomy among serotype III isolates, and the existence of an unlimited number of carrier clones of type III and other serotypes with a restricted number of clones that cause invasive infections.…”

“…Because serotype III accounts for more than two-thirds of all GBS-related neonatal disease cases [2], serotyping was proposed as a means of predicting risk of invasive disease. However, serotype III is also frequently isolated in asymptomatically colonized infants, serotypes other than type III are frequently isolated in early-onset disease, and as many as 10 -15% of GBS isolates were nontypable in some studies [2,4,23].…”

“…A number of molecular methods have been used for subtyping GBS isolates and correlating particular genotypes with disease [3,4,8,9,18]. Musser et al [13], examining 128 GBS isolates by multi-locus enzyme electrophoresis, found that type III strains belonged to two distantly related evolutionary lineages.…”

Streptococcus agalactiae: a vaginal pathogen?

“…Streptococcal strains were identified by gram-staining, production of catalase, CAMP test, serogrouping and the API20 Strep system (API System, bioMerieux, France). sensitised with purified rabbit immunoglobulins specific for each of the three types (Pastorex B streptococci; Diagnostics Pasteur) [8].…”