Capsular switching in group B Streptococcus CC17 hypervirulent clone: a future challenge for polysaccharide vaccine...

Area of Science:

• Microbiology
• Genetics
• Vaccinology

Background:

• Group B Streptococcus (GBS) is a major neonatal pathogen.
• Capsular polysaccharide (CPS) is a key virulence factor and vaccine target.
• Hypervirulent GBS CC17 strains were previously exclusively CPS type III.

Purpose of the Study:

• Investigate capsular polysaccharide (CPS) types in French invasive GBS strains.
• Characterize GBS CC17 strains exhibiting non-type III CPS.
• Understand the genetic basis of CPS switching in GBS.

Main Methods:

• CPS typing of 965 GBS strains.
• Investigation of the hvgA gene in CC17 strains.
• MLST, PFGE, and whole genome sequencing of CPS type IV CC17 strains.

Main Results:

• Three hvgA-positive GBS strains were identified as CPS type IV.
• MLST and PFGE confirmed a capsular switch from type III to type IV in CC17.
• Whole genome sequencing revealed a 35.5-kb DNA fragment exchange encoding the cps operon.

Conclusions:

• GBS CC17 hypervirulent strains have undergone a significant capsular switch, altering a primary vaccine target.
• Continued GBS population surveillance is crucial, especially during conjugate vaccine clinical trials.