MOLECULAR ANALYSIS OF MULTIPLE ISOLATES OF THE MAJOR SEROTYPES OF GROUP-B STREPTOCOCCI

Serotyping of clinical isolates is a widely used technique for epidemi ologic study of group B streptococcal infections. However, serotyping cannot definitively determine epidemiologically related or unrelated i solates. We investigated the use of restriction endonuclease analysis (REA) with both conventional agarose gel electrophoresis (AGE) and pul sed-field gel electrophoresis (PFGE) in 50 isolates of the major serot ypes of group B streptococci. Single digestion with HindIII and HaeIII and double digestion with HindIII and then EcoRI were used for conven tional AGE, and digestion with SmaI was used for PFGE. The molecular p rofile of one strain was compared with those of the strains within the same serotype as well as with the profiles from strains of different serotypes. Among 10 type Ia, Ia/alpha, Ia/alpha+beta, and Ia/R1 isolat es and depending on the restriction enzyme used, we found between five and six REA patterns by conventional AGE and seven by PFGE; among 4 t ype Ib/alpha+beta isolates we found 2 to 4 REA patterns by conventiona l AGE and 4 by PFGE; among 21 type II, II/alpha, II/beta, II/alpha+bet a, and II/R4 isolates, we found 11 REA patterns by both AGE and PFGE; and among 14 type III, III/R1, and III/R4 isolates, we found from 7 to 12 different REA patterns by AGE and 10 by PFGE. In total, among 13 s erotypes and one nontypeable strain, we found 29 to 31 REA patterns by conventional AGE and 33 by PFGE. A particular REA pattern found withi n a serotype was different from the patterns found in the other seroty pes, suggesting that REA analysis by using conventional AGE or PFGE is a sensitive method for analyzing genetic relatedness and diversity in group B streptococci and has potential value in molecular epidemiolog ic studies.