MOLECULAR ANALYSIS OF CLINICAL GROUP-B STREPTOCOCCAL STRAINS BY USE OF ALPHA-GENE AND BETA-GENE PROBES

Group B streptococci (GBS) are a leading cause of neonatal sepsis and meningitis. Besides the type-specific capsule, which is considered to be a major virulence factor of the species, some proteins are believed also to be virulence determinants and have been found to elicit prote ctive immunity. In the present work, the genes for two surface protein s, the alpha and beta antigens, were detected in hybridization tests w ith chromosomal DNA of clinical GBS isolates. Using as a probe a PCR-g enerated 1.5 kb part of the beta gene, hybridization was found for 4/1 9 type Ia, 8/11 type Ib, 5/6 type II but for 0/8 type III strains. Pos itive outcome of hybridization coincided with an ability of the strain s to bind IgA. A 200 bp alpha gene probe hybridized with all tested st rains of serotypes Ia, Ib or II but only with 4/17 type III strains. B y Southern blot, it was found that the size of the EcoRI chromosomal g ene fragments hybridizing with the alpha gene probe correlated with th e genomic presence or absence of the beta gene, possibly reflecting ev olutionary relationship between the two genes. This assumption was fur ther supported by pulsed field gel hybridization analysis which, howev er, showed the chromosomal positions of these two genes not to be adja cent.