Changing the Phase of Salmonella

The majority of serotypes of Salmonella possess two phases of H (flagellar) antigens. If agglutination is obtained with one phase, the organism may be induced to change to the other phase.

Most isolates exist in two phases: phase 1, phase 2 or may have both phases simultaneously. Cultures that are not expressed in one phase upon primary culture may be switched to the other phase using 2 methods: a Craigie’s tube or ditch plate (Jamieson’s plate1-3). Both methods involve adding the test organism to the H anti-serum which it has already agglutinated with. Organisms in the original phase demonstrated, agglutinate with the H anti-serum, leaving the organisms in the alternative phase free to move in the culture.

To understand more about this, please refer to a technical report from Public health England here.

Posted by Tim Sandle