ATCvet code: QI01AE01.
To stimulate active immunity against Salmonella Typhimurium, phage type 204.
The vaccine strain is a natural metabolic drift mutant of Salmonella Typhimurium phage type 9, that is it lacks or does not express certain metabolic pathways which result in attenuation.
The genetic basis results in defective gyrase affecting DNA replication (nalidixic acid resistance) and defective RNA polymerase affecting transcription of DNA to RNA (rifampicin resistance).
The vaccine strain also has attenuations that increase the permeability of the cell membrane to noxae such as detergents and antibiotics. This means the strain has poor survival in the environment and is sensitive to fluoroquinolones and unlike field strains is sensitive to erythromycin.