Molecular Characterization of Nontypeable Group B Streptococcus

Abstract

Traditionally, the capsular polysaccharide (CPS) antigen has been used to distinguish between the nine known serotypes of group B streptococcus (GBS) by classical antibody-antigen reactions. In this study, we used PCR for all CPSs and selected protein antigens, multilocus sequencing typing (MLST), and pulsed-field gel electrophoresis (PFGE) to molecularly characterize 92 clinical isolates identified as nontypeable (NT) by CPS-specific antibody-antigen reactivity. The PCR and MLST were performed on blinded, randomly numbered isolates. All isolates contained the cfb gene coding for CAMP factor. While most (56.5%) contained a single CPS-specific gene, 40 isolates contained either two or three CPS-specific genes. Type V CPS-specific gene was present in 66% of the isolates, and all serotypes except types IV, VII, and VIII were represented. Most (44.5%) of the isolates contained a single protein antigen gene (bca, bac, rib, alp1, or alp3), and the remaining isolates had multiple protein antigen genes. Of the 61 isolates that had the V CPS-specific gene, 48 (78.6%) had the alp3 gene. PFGE analysis classified the isolates into 21 profile groups, while MLST analysis divided the isolates into 16 sequence types. Forty-two (69%) of 61 isolates with the V CPS-specific gene were in PFGE profile group 4; 41 of these 42 were sequence type 1 by MLST. These data shed new light on the antigenic complexity of NT GBS isolates, information that can be valuable in the formulation of an effective GBS vaccine.

Molecular Epidemiology and Distribution of Serotypes, Surface Proteins, and Antibiotic Resistance among Group B Streptococci in Italy

“…Representatives of this group displayed ST1, and the only serotype IV isolate exhibited ST196, a DLV of ST1. NT isolates closely related to type V isolates, as determined by PFGE, have been described previously (1), and NT isolates ultimately classified as ST1 in the present study have been previously reported to carry the capsular polysaccharide synthesis-specific gene characteristic of serotype V (35). Indeed, isolates of serotypes IV and V have been previously described as belonging to CC1 (29).…”

“…DNA was extracted as previously described (13) and digested with 40 U of SmaI. PFGE results were interpreted according to the criteria previously reported (35). Isolates with indistinguishable PFGE patterns were assigned to identical PFGE subtypes.…”

International External Quality Assurance for Laboratory Identification and Typing of Streptococcus agalactiae (Group B Streptococci)

“…Furthermore, this method could be a useful adjunct for vaccine development and surveillance, as it identifies GBS strains that are serologically nontypeable. Nontypeable strains often have CPS genes but are low-level producers or may have modified capsular structures that do not react to antisera from any of the 10 known serotypes (25). Another serotyping method, used by 2 of 14 participating centers, included immunodiffusion with in-house antisera.…”

The Threat of Aerobic Vaginitis to Pregnancy and Neonatal Morbidity

“…The gastrointestinal tract serves as the natural reservoir for GBS and is expected to be the source of vaginal colonization 23,43 . Pregnant women who are colonized with GBS might develop infections of the urinary tract, bacteremia, chorioamnionitis, and postpartum endometritis 23,47,48 , thus increasing the risk of PTD, PPROM and perinatal transmission [49][50][51] , resulting in neonatal sepsis and meningitis 45,52,53 . A prevalence of 7 -25% GBS colonization in AV has been reported in women between 35 and 37 weeks of gestation 54 , with intrauterine infection associated with the ability of GBS to ascend from the lower genital tract and colonize the upper genital tract [54][55][56] .…”