Molecular characterization of nontypeable group B streptococcus

Area of Science:

• Microbiology
• Immunology
• Vaccinology

Background:

• Traditional serotyping of group B Streptococcus (GBS) relies on capsular polysaccharide (CPS) antigens, distinguishing nine known serotypes.
• Nontypeable (NT) GBS isolates present challenges for accurate classification and vaccine design.
• Understanding the genetic diversity of NT GBS is crucial for developing effective GBS vaccines.

Purpose of the Study:

• To molecularly characterize 92 clinical isolates of nontypeable GBS.
• To investigate the genetic basis of antigenic complexity in NT GBS.
• To provide insights for the development of a comprehensive GBS vaccine.

Main Methods:

• Polymerase chain reaction (PCR) was used to detect CPS and protein antigen genes.
• Multilocus sequencing typing (MLST) and pulsed-field gel electrophoresis (PFGE) were employed for molecular subtyping.
• Antibody-antigen reactivity was used to identify nontypeable isolates.

Main Results:

• All 92 NT GBS isolates contained the CAMP factor gene (cfb).
• Forty isolates possessed multiple CPS-specific genes, with Type V CPS-specific gene found in 66% of isolates.
• MLST identified 16 distinct sequence types, and PFGE revealed 21 profile groups, with significant overlap between Type V CPS, alp3, PFGE group 4, and MLST sequence type 1.

Conclusions:

• Nontypeable GBS isolates exhibit significant antigenic complexity, with multiple CPS and protein antigen genes.
• The prevalence of Type V CPS and specific MLST/PFGE profiles suggests potential clonal expansion or common genetic background.
• These findings are valuable for understanding GBS diversity and guiding the development of a broadly protective GBS vaccine.