serogroups

A serogroup is a classification of a bacterial or viral population based on shared surface antigens that are recognized by the immune system. The grouping is defined by serological properties detected with antibodies, typically using agglutination, precipitation, or immunoassays. In many bacteria, serogroups correspond to variation in surface polysaccharides or capsules (and sometimes flagellar or O-antigen structures). Serogroups reflect antigenic diversity that arises through genetic variation and horizontal gene transfer, and they can influence pathogenicity and epidemiology. A species may contain multiple serogroups, with many also containing multiple serotypes within each serogroup; the terms serogroup, serotype, and serovar are related but used differently across organisms.

Commonly cited examples include Neisseria meningitidis, whose serogroups A, B, C, W, X, and Y are used to describe epidemic potential and vaccine coverage; Vibrio cholerae is organized into serogroups, notably O1 and O139, which are associated with epidemic cholera outbreaks. In other pathogens such as Salmonella and Streptococcus pneumoniae, serogrouping is part of the broader system of serotyping used in diagnostics and surveillance.

Determination of serogroups relies on serological testing against specific surface antigens; increasingly, molecular methods target the genes responsible for the relevant antigens, enabling rapid and precise classification. Understanding serogroups aids in vaccine design, outbreak investigation, and tracking the spread of disease because certain serogroups may predominate in particular times or geographic regions.