Plasmid profile typing can be used to subdivide phage-type 49 of Salmonella typhimurium in outbreak investigations.

Plasmid profile typing has been used to subdivide phage-type 49 of Salmonella typhimurium, the most common phage type in humans in England and Wales since 1985. Twenty profile patterns have been identified in 350 strains examined. Four profile patterns have been identified in 143 isolates from patients infected in 33 epidemiologically unrelated incidents and two patterns have predominated, ST49:62 and ST49:62, 1. These patterns were also common amongst S. typhimurium phage-type 49 isolated from cattle and poultry; however ST49:62 was more common in bovines whereas ST49:62, 1 predominated in poultry. S. typhimurium phage-type 49 with a different profile pattern, ST49:62, 3, was responsible for a large outbreak in London in 1988 which was traced to mayonnaise made from eggs supplied by one producer. Plasmid profile typing can now be regarded as a method of supplementing phage typing in investigating outbreaks caused by this organism.