Distribution of pulsed-field gel electrophoresis types of invasive Norwegian group B streptococci in relation to serotype

A collection of 78 invasive GBS isolates representing the most common serotypes were characterized by PFGE of SmaI digested chromosomal DNA. Three strains were non-typeable by PFGE, and 11 strains were nontypeable by capsular polysaccharide serotyping (NT). Pulsotypes were compared and classified in dendrograms by using Jaccards coefficient with 2.5% band tolerance and the unweighted pair group method with arithmetic averages. Among the 75 strains typeable by PFGE, a total of 62 different restriction profiles were identified, confirming the genetic diversity also shown by others. At 85- and 80% similarity level, 53 and 50 different PFGE patterns, respectively, were identified. PFGE patterns within each serotype differed considerably. The largest degree of heterogeneity was observed in serotype IV, 6 profiles in 6 strains, and in serotypes Ia and II, both 10 profiles among 12 strains. Serotype Ib, III, and V were more homogeneous: 6 profiles in 11 strains, 7 profiles in 11 strains, and 8 profiles in 12 strains, respectively. Two and one NT strains showed an identical profile with a cluster of serotype V and serotype Ib strains, respectively. Any isolate among the isolates investigated showing greater than 88% similarity to a restriction profile in the database, could correctly be ascribed to a capsular polysaccharide serotype.