Characterization of new Salmonella serovars by whole-genome sequencing and traditional typing techniques

Abstract

Serotyping forms the basis of all national and international surveillance networks for Salmonella. Public health microbiology is currently being transformed by high-throughput DNA sequencing, which opens the door to serovar determination using this powerful technique. Twenty-nine Salmonella isolates referred to the Public Health England between 1994 and 2004 for serovar identification were selected for this study, and they all presented with novel antigenic formulae. Results from a combination of traditional phenotypic and molecular assays were compared. Twenty-two isolates (76 %) were subsequently independently confirmed as new types; of these, 18 (82 %) were grouped as Salmonellaenterica subspecies I, and four (18 %) were S. enterica subspecies II. In general, it is shown that there is concordance between the DNA sequence type and traditional phenotypic serotype, but it would be necessary to analyse a larger data set to confirm this. Traditional multilocus sequence typing (MLST) by Sanger sequencing also correlates to insilico whole-genome sequencing MLST. This permits the continuation of traditional serovar nomenclature alongside sequence type methods and enhances the ability to infer true phylogenetic relationships between isolates.