Serotype IX, a Proposed New Streptococcus agalactiae Serotype.

Area of Science:

• Microbiology
• Immunology
• Genetics

Background:

• Streptococcus agalactiae, or group B Streptococcus (GBS), is a significant human pathogen.
• Existing GBS serotyping methods rely on specific antisera, but some strains remain untypeable.

Purpose of the Study:

• To investigate and characterize previously untypeable GBS isolates.
• To identify and define a potential new GBS serotype.

Main Methods:

• Development of novel polyclonal rabbit antisera against untypeable GBS isolates.
• Utilized capillary precipitation and Ouchterlony tests for serological comparison.
• Employed Western blotting and PCR for molecular characterization, including analysis of the cps gene cluster and surface protein genes (bca, bac).
• Sequencing of specific segments within the cps gene cluster.

Main Results:

• Three human GBS isolates were initially identified as untypeable with existing antisera.
• New antisera successfully reacted with these isolates, suggesting a distinct serotype.
• Testing of 227 additional GBS isolates revealed five more strains reacting with the new antisera, totaling eight isolates.
• All eight isolates expressed Calpha protein, and seven expressed Cbeta protein.
• Unique partial cps gene sequences were identified in all eight isolates.
• A shared, unique partial cps sequence confirmed these isolates represent a new serotype.

Conclusions:

• The eight investigated isolates represent a novel, previously unrecognized GBS serotype.
• The proposed designation for this new serotype is Streptococcus agalactiae serotype IX.
• This discovery expands the GBS serological classification and improves diagnostic capabilities for GBS identification.