serotyping

Serotyping is a laboratory method used to classify microorganisms based on the antigenic properties of their surface structures. In bacteria, serotypes are defined by combinations of surface antigens such as O polysaccharides, H flagellar proteins, and, in some species, capsule (K) antigens. The resulting serogroups or serotypes help distinguish strains within a species and track patterns of transmission and disease.

Traditional serotyping relies on serological reactions with panels of antibodies directed against specific antigens. Agglutination tests, performed on slides or in microtitre plates, indicate the presence of particular antigens and thus identify the serotype or serogroup. Modern approaches also employ monoclonal antibodies or DNA-based tests that infer serotype from antigen loci, sometimes referred to as molecular serotyping. In Salmonella, the Kauffmann-White scheme remains a classic reference that maps combinations of O and H antigens to defined serotypes.

Serotyping is widely used in clinical microbiology, public health, and epidemiology. It informs outbreak investigations, surveillance, vaccine formulation, and studies of pathogenicity and host range. Common serotyped organisms include Salmonella enterica, Escherichia coli (O and H antigens), Streptococcus pneumoniae (capsular serotypes), Neisseria meningitidis (capsular serogroups), and Vibrio cholerae (O1 and O139 serogroups).

Limitations of serotyping include cross-reactivity of antisera, dependence on reference strains, and the need for skilled interpretation. Some organisms exhibit extensive serotype diversity, while others lack stable surface antigens. Serotyping is often complemented by genetic typing methods to assess relatedness and evolution.