serogrouping

Serogrouping is the classification of bacterial strains into serogroups based on shared antigenic properties exposed on the cell surface, most commonly polysaccharide capsules or somatic O antigens. The approach is used to organize diverse strains for epidemiological surveillance, vaccine development, and clinical diagnostics. Serogroups reflect groups of strains that share specific antigenic determinants recognized by antibodies.

Serogrouping is typically performed with serological assays that detect targeted surface antigens. Common methods include slide or tube agglutination with specific antisera, latex particle agglutination, and microtiter plate–based immunoassays. Molecular techniques, such as PCR assays targeting capsule biosynthesis genes or sequencing-based approaches, can infer serogroups when traditional serology is inconclusive or impractical. In some contexts, serogrouping is complemented by broader typing strategies, including serotyping or genotyping, to resolve finer distinctions among strains.

The concept of a serogroup differs from serotype, though the terms are related. A serogroup groups strains by a defined set of antigens, while a serotype often denotes a specific combination of antigenic determinants within or across serogroups. The distinction can vary by organism and field of study.

Examples of serogrouping use include Neisseria meningitidis, where serogroups such as A, B, C, W, X, and Y are defined by capsule antigens; Streptococcus pneumoniae and Salmonella enterica also utilize serogroup/serotype classifications based on capsule or O-antigen profiles. Serogroup information informs vaccine coverage decisions and helps track the spread of particular lineages during outbreaks. Modern practice increasingly complements serogroup data with genomic typing for greater resolution.