Epidemiological markers of strains of Salmonella are classified as major or minor. Major epidemiological markers are determined by chromosomal genes and are not affected by extrachromosomal elements. They are subspecies and serovars. Minor epidemiological markers are either affected by extrachromosomal replicons or have an insufficiently proven genetic stability and are used to subdivide serovars in detailed epidemiological investigations. These minor markers are biovars, phagovars, bacteriocinovars, patterns of resistance to antimicrobial agents, and restriction patterns of chromosomal and plasmid DNA.