Classification and Nomenclature of Enteric Fever
المؤلف:
APURBA S. SASTRY , SANDHYA BHAT
المصدر:
Essentials Of Medical Microbiology 2021
الجزء والصفحة:
3rd edition , p302-303
2025-10-23
39
Salmonella is a gram-negative bacterium, belongs to the family Enterobacteriaceae.
- The credit of discovery of ‘Salmonella’ goes to Salmon and Smith (1885)
- The most important serotype of Salmonella, S. Typhi, was first observed by Eberth (1880) and Gaffky (1884) and hence was formerly called Eberth-Gaffky bacillus or Eberthella Typhi.
Salmonella is antigenically complex. The classification and nomenclature of salmonellae have undergone several modifications over the past years. There are several classifications proposed so far.
Clinical Classification
It is the oldest, user friendly classification which is still widely used. It divides salmonellae into two groups:
1. Typhoidal Salmonella: It includes serotypes S. Typhi and S. Paratyphi. They are restricted to human hosts, in whom they cause enteric fever (typhoid/paratyphoid fever)
2. Non-typhoidal salmonellae or NTS: The remaining serotypes can colonize the intestine of a broad range of animals, including mammals, reptiles, birds and insects. They also infect humans causing food-borne gastroenteritis and septicemia.
Antigenic Classification (Kauffmann–White Scheme)
The classification within the genus is based on the presence of different somatic (O) and flagellar (H) antigens which can be detected by agglutination with the respective antisera (Table 1).
- Serogroups: Based on O antigen, salmonellae are initially classified into serogroups:
* Earlier, serogroups were named as letters, e.g. A, B, C and so on
* However, as the numbers increased, the serogroups are re-designated as numbers, e.g. 1, 2, 3 and so on
* Currently, there are up to 67 serogroups, each containing group-specific O antigen, for example:
● Serogroup-2 (formerly, serogroup A)—contains group specific O antigen type 2
● Serogroup-4 (formerly, serogroup B)—contains group-specific O antigen type 4
● Serogroup-9 (formerly, serogroup D)—contains group specific O antigen type 9.
- Serotypes: Each serogroup is further differentiated into serotypes, based on the type of flagellar antigens present. Currently, there are more than 2,500 serotypes of salmonellae.
Table1. Kauffmann–White antigenic classification for Salmonella.
Molecular Classification
Based on DNA hybridization studies, the genus Salmonella consists of two species—(1) Salmonella enterica, and (2) S. bongori.
- Within the species S. enterica, there are six subspecies; namely enterica, salamae, arizonae, diarizonae, houtenae and indica
- Each subspecies is further differentiated into serotypes (based on O and H antigens as described in the Kauffmann–White scheme) (Table 1)
- Most of the pathogenic typhoidal and non-typhoidal Salmonella serotypes are placed under species enterica and subspecies enterica.
Nomenclature
Taxonomically, the correct nomenclature of the members of salmonellae is very much complicated, e.g. Salmonella species enterica subspecies enterica serotype Typhi.
However, for routine use a simplified format is followed where only the genus and serotype names are included, for example Salmonella serotype Typhi or in short, S. Typhi.
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