Salmonella serotyping 

Salmonella are a family of bacteria which live in the intestinal tracts of many animals, including reptiles, birds and mammals. Within this family there are more than 2,500 known serotypes of bacteria, with people most often being affected if they eat contaminated food. However, animal owners can be at risk of becoming infected through the faeco-oral route if their health and safety standards are not satisfactory.  

Salmonella serotyping allows us to differentiate serological varieties of the genus by determining which surface antigens are being produced by the bacterium. This is important as it gives us more information regarding the pathogenicity of the organism that has been isolated. 

First the “O” antigen is determined.  The bacterial outer membrane is covered with lipopolysaccharides, of which the outermost portion is the O antigen.  

Then the “H” antigen is determined which denote the proteins that are associated with the bacterial flagella, or whip-like tail which the bacteria use to move around.  

Salmonella exist in both a motile and non-motile phase, with different H antigens being produced depending on the phase in which the bacterium is found. 

Once identified, different subspecies can then be further grouped into serogroups, including A, B, C, D, E and so on, e.g. within the S. enterica subspecies I, the most common O-antigen serogroups are A, B, C1, C2, D and E. Strains in these serogroups cause approximately 99% of Salmonella infections in humans and warm-blooded animals. Although strains within the A, B and C serogroups appear to have the highest pathogenicity, all strains of this bacteria can potentially cause disease, especially in immunocompromised individuals, including the very young, old or those receiving immunomodulatory drugs e.g. chemotherapy.  

If a Salmonella has been identified from a sample you have submitted, treating this bacterium would always be recommended, along with establishing strict health and safety regimes within the household to prevent further spread to any other in contact animals or people. Keeping a salmonella positive animal away from anyone who is immunocompromised is of utmost importance. 



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