Serogroup

A serogroup is a classification in microbiology that groups strains of a species by shared serologic properties, usually by surface antigens such as polysaccharide capsules or lipopolysaccharide O antigens. Serogroups reflect common immune reactivity and are used to organize strains beyond their genetic lineage. Within a species, multiple serogroups may exist, and a single serogroup can contain several serotypes or variants.

Serogroups are determined by serological testing, typically using specific antisera that cause agglutination or other antibody-based reactions. Traditional methods include slide or tube agglutination and enzyme-linked assays, while modern approaches frequently use molecular techniques to infer serogroup from gene clusters responsible for antigen synthesis, providing faster or higher-resolution results.

Examples illustrate the practical importance of serogroups. Neisseria meningitidis is divided into serogroups A, B, C, W, Y, and X, with serogroup distribution influencing vaccination strategies and outbreak response. Vibrio cholerae serogroups O1 and O139 are notably linked to epidemic cholera, and Escherichia coli strains are categorized into numerous O serogroups based on their O antigen, often combined with H antigens to describe serotypes. Serogroup information supports epidemiology, vaccine design, and public health surveillance by highlighting prevalent or regionally shifting antigenic types and potential differences in pathogenicity or antibiotic susceptibility.

Limitations include possible cross-reactivity or non-expression of target antigens in some conditions, and the fact that serogroup affiliation does not always align with genetic relatedness. Molecular typing and genome-based methods increasingly complement traditional serology to provide higher-resolution classification.