Salmonellae are ubiquitous human and animal pathogens. They colonize virtually all animals including poultry, birds, livestock, reptiles, rodents, domesticated animals, and humans.
Salmonella infections in humans typically produce one ofthree clinical syndromes, such as gastroenteritis, enteric fever, or focal disease. In addition, Salmonella infection in animals causes substantial losses of livestock.
Salmonella spp. include Gram-negative, flagellated, and facul-tative anaerobic bacilli characterized by the presence of O, H, and Vi antigens. The taxonomic classification of the genus Salmonella is complex and problematic:
· Based on DNA homology and host range, the genus Salmo-nella is classified into two species: Salmonella Enterica and SalmonellaBongori. S. Enterica is further subdivided into sixsubspecies I, II, IIa, IIIb, IV, and VI.
· Most of the salmonellae that are pathogenic to human beings belong to the subgroup I of S. Enterica subsp. enterica. This includes the typhoid and paratyphoid bacilli and most other serotypes responsible for diseases in mammals.
· Additionally, each of the Salmonella isolates is serotyped according to the presence of particular somatic O, flagel-lar H, and surface Vi antigens. Presently more than 2400 serotypes are described.
· The salmonella serotype is unique in the sense that each Salmonella serotype is considered as a species.
Salmonellae serotypes are named as, for example, S. Enterica subsp. enterica serotype Enteritidis. However, for the sake of convenience, it is abbreviated as S. Enteritidis or just Enteritidis for use in clinical situations. In addition, serotypes are not mentioned in italic but in Roman. Human infections caused by Salmonella spp. are summarized in Table 32-1.