Molecular genetic determinants of virulence of Streptococcus agalactiae isolated from pregnant women and newborns in St. Petersburg and the Leningrad region in 2010–2023

Abstract

Introduction. Colonization of the reproductive organs of pregnant women with group B streptococci (GBS; Streptococcus agalactiae) can lead to severe perinatal and neonatal pathology. In modern conditions, aside from the prevention of antenatal infection of the fetus during childbirth using antibacterial drugs, vaccination is also necessary. In this regard, surveillance of GBS genotypes is an important task. Objective. To determine the molecular genetic determinants of virulence of Streptococcus agalactiae isolated from pregnant women and newborns, and to monitor the distribution of capsular polysaccharides types and pili profiles in GBS clinical isolates. Materials and methods. The study used clinical isolates of GBS (n = 420) isolated from pregnant women and newborns in 2010–2023.The bacteriological method was used for isolation of S. agalactiae. PCR method was used to determine the types of capsular polysaccharides, pili, and whether the strains belonged to the hypervirulent sequence type ST-17. Results. During 13 years of observation, the predominance of Ia, III and V genotypes of GBS capsular polysaccharides was noted both in pregnant women and in newborns. The frequency of occurrence of genotype Ib increased from 0.7 to 6.7%, genotype V from 12.1 to 24.4%, and the prevalence of genotype III decreased significantly from 41.1 to 21.1%. Hypervirulent sequence type ST-17 was detected in 6 pregnant women and 2 newborns. However, there were no signs of neonatal infection in these children. More than half of all clinical isolates of S. agalactiae had pili genotypes PI-1 + PI-2a, as well as pili genotypes PI-2a and PI-1 + PI-2b. The distribution of pili types did not change over 13 years of the surveillance period. Conclusion. Surveillance of the GBS capsular polysaccharides and pili genotypes is necessary for the development of effective preventive vaccines.