serovar

A serovar, short for serological variant, is a taxonomic category used in microbiology to classify distinct strains within a species based on differences in surface antigens. These antigenic differences are detected by serological tests that use antibodies to recognize specific components on the organism’s surface, such as polysaccharide or protein antigens.

In bacteria, serovars are commonly defined by combinations of O (somatic) and H (flagellar) antigens, and sometimes by capsule (K) antigens. The most widely cited example is the Kauffmann–White scheme for Salmonella enterica, which assigns serovars like Typhi or Typhimurium according to their O and H antigen profiles. Other genera, including Escherichia, Listeria, and Campylobacter, also have serovar classifications based on similar antigenic differences.

Serovars are important for epidemiology, surveillance, and public health. They enable tracking of transmission routes during outbreaks, inform diagnostic testing, and guide vaccine development by identifying antigenically relevant variants. Many bacterial species exhibit numerous serovars, reflecting diversity in surface antigens, while others have relatively few.

Identification and classification of serovars primarily rely on serotyping methods, though genomic approaches such as multilocus sequence typing and whole-genome sequencing are increasingly used and can reveal diversity not evident from serology alone. Serovar designations may change with new data or revised schemes, illustrating the ongoing relationship between antigenic typing and genetic characterization. The term is most closely associated with bacteria; in virology, the equivalent concept is generally referred to as a serotype rather than a serovar. The word serovar derives from serology, the study of antibodies and antigens.