|Abstract||This National Standard Method (NSM) describes the identification of Salmonella species. The|
majority of Salmonellae are isolated from faeces but the organism may be isolated from other
specimens such as blood, bone marrow and urine.Issue 2.1
Serotypes of Salmonella and Arizona belong to the family Enterobacteriaceae and are now considered to belong to two species Salmonella Bongori (formerly subspecies V) and Salmonella Enterica (comprising six subspecies: I = enterica, II = salamae, IIIa = arizonae, IIIb = diarizonae, IV = houtenae, and VI = indica). Most (>99.5%) salmonella isolates from humans are serotypes of Salmonella Enterica.
The nomenclature adopted in this NSM follows the advice from the Judicial Commission of the
International Committee on Systematics of Prokaryotes. It is likely however, that laboratories will
continue to report serotypes as species for some time to come.
Salmonella species are Gram-negative rods. On blood agar, colonies are 2 - 3 mm in diameter.
Colonies are generally lactose non-fermenters. Salmonella species are motile (with a few exceptions), facultatively anaerobic, produce acid from glucose usually with the production of gas, and are oxidasenegative. Most produce hydrogen sulphide except Salmonella Paratyphi A and Salmonella Typhi, which is a weak producer. They are identified with a combination of serological and biochemical tests.
Salmonella species are classified and identified into serotypes according to the Kauffmann-White
scheme, which currently contains in excess of 2000 serotypes. Primary subdivision is into “O”
serogroups (those which share a common somatic antigen), and these are then subdivided on the basis of “H” (flagella) antigens. Strains of Salmonella Typhi may produce Vi antigen, which is an acidic polysaccharide layer outside the cell wall. When fully developed it renders the bacteria
agglutinable with Vi antiserum and inagglutinable by “O” antiserum. Antigens similar to Vi may also be found in some strains of Salmonella Paratyphi C and Salmonella Dublin.
Laboratory acquired infections of salmonella including Salmonella Typhi have been reported.
Principles of identification:
Isolates are identified by a combination of colonial appearance, serology (agglutination with specific antisera) and biochemical testing. If confirmation of identification is required, isolates should be sent to the Reference Laboratory.