Multiple Genetic Typing of Salmonella enterica Serotype Typhimurium Isolates of Different Phage Types (DT104, U302, DT204b, and DT49) from Animals and Humans in England, Wales, and Northern Ireland

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Abstract
Salmonella enterica serotype Typhimurium is a common cause of salmonellosis among humans and animals in England, Wales, and Northern Ireland. Phage types DT104 and U302 were the most prevalent types in both livestock and humans in 2001. In addition, Salmonella serotype Typhimurium DT204b was responsible for a recent international outbreak involving England. A total of 119 isolates from humans ( n = 28) and animals or their environment ( n = 91), belonging to DT104 ( n = 66), U302 ( n = 33), DT204b ( n = 12), and DT49 ( n = 8), were fingerprinted by a combination of well-established genetic methods (pulsed-field gel electrophoresis [PFGE], Pst I/ Sph I [PS] ribotyping, and plasmid profiling). The different techniques identified different degrees of polymorphism (from greatest to least, plasmid profiling [40 types], PS ribotyping [34 types], and PFGE [23 types]). It seems clear that a prevalent genomic clone, as well as a variety of less frequent clones, is present for each of the phage types. In most cases, the prevalent clones appeared within isolates from several animal species and from several geographical locations. We did not find clear evidence of a higher degree of diversity for any of the animal species included, or of any link between isolates from particular animal species and humans. The data presented show the inaccuracy of drawing epidemiological conclusions based on a single fingerprinting method. Strains that share one of the markers do not necessarily belong to the same clone, and a multiple typing approach is required to enable enough discrimination to track strains for epidemiological investigations.