During the past several decades Streptococcus agalactiae has emerged as the major cause of bacterial infection in newborns with a high rate of mortality.In the present study the maternal colonisation, the distribution of serotypes, the efficacy of intrapartum antibiotic-prophylaxis and the prevalence of same factor of virulence have been estimated. Particularly on GBS isolates a study has been made to identify the genes of surface proteins "alp", biofilm formation, antimicrobial susceptibility and macrolide resistence genotypes.A total of 60 women at 35th-37th week of gestation were enrolled, to these, during the screening for prevention of perinatal GBS disease, double samples have been made, from the vagina and the rectum. About 12% of the pregnant women was colonised by GBS and the characterized serotypes were: Ia, III and V.About 72% of the isolated GBS express "alp" proteins. The greater biofilm …