Serotyping of Salmonella: Introduction, Types and Risk Factors of Salmonella Infection


Salmonella Serotyping

Serotyping is a type of epidemiological marker.

It works on the principle of agglutination.

agglutination or clumping: positive

No agglutination or clumping: Negative

On this basis, Salmonella can differentiate whether Salmonella enterica serotype  Typhi or Paratyphi and so on.


Serotype                                                     O antigen

Salmonella enterica serotype  Typhi         9, 12, Vi

( Weak H2S production in SIM or TSI agar)


Salmonella enterica serotype  Paratyphi A    1, 2, 12

( No H2S production in SIM or TSI agar)


Salmonella enterica serotype  Paratyphi B    1, 4, 5, 12

( Strong H2S production and gas in SIM or TSI agar)

Serotypes are groups within a single species of microorganisms like bacteria or viruses, that share distinctive surface structures. For instance, Salmonella bacteria look similar under the microscope but can be separated into many serotypes based on two structures on their surface:

The outermost portion of the bacteria’s surface covering, called the O antigen or somatic antigen where as ; and slender threadlike structure, called the H antigen or flagellar antigens , that is part of the flagella.
The O antigens are distinguished by their different chemical make-up. The H antigens are distinguished by the protein content of the flagella. Each O and H antigen has a unique code number that helps to  determine the serotype based on the distinct combination of O and H antigens as shown above picture.

Different Serotypes

More than 2,500 serotypes have been described so far for Salmonella; among them, less than 100 serotypes account for most human infections.

The nature and distribution of serotypes vary from serotype to serotype. e.g.  Some serotypes are only found in one kind of animal or in a single place, where as others are found in many different animals and all over the world. Some can cause especially severe illnesses when they infect people; while others cause milder illnesses.

List of some common serotypes of Salmonella

  • Salmonella enterica serovar Typhimurium
  • Salmonella enterica serovar Enteritidis
  • Salmonella enterica serovar Newport
  • Salmonella enterica serovar Heidelberg
  • Salmonella enterica serovar Javiana

Risk Factors of Salmonellosis 

  1. Older adults
  2. People with weakened immune systems
  3. children under five years old


  1. Serotyping is a subtyping test based on differences in microbial (e.g., viral or bacterial) surfaces.
  2. Serology refers to the antibodies that form because of a viral or bacterial infection.
  3. Serotyping is sometimes referred to as serology, but this is technically inaccurate.
  4. A serotype is also called serovar, is a distinct variation within a species of bacteria or virus or among immune cells of different individuals.
  5. Salmonella enterica has more than 2300 serotypes based on “O” antigen, H antigen, and Vi antigen (in Kauffman- White scheme).

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