Development and application of molecular typing methods for <em>Salmonella spp</em> - The UK experience

Abstract

For the itlentification and typing of salmonellas the policy of the Laboratory of Enteric Pathogens is to use a hierarchical approach based in the first instance on phenotypic subdivion, supplementeel when appropriate by ntethods based on the analysis of plasmid DNA antl chromosomal DNA (genotyping). Plasmid DNA-based methods inclttde plasmid profiIe typing, plasmicl fingerprinting and the identification of plasmid-encoded salmonella plasmid virulence (spv) genes. Genotyping ntethods include ribotyping, insertiort sequence (lS) 200 fingerprinting and pulsed-field gel electrophoresis (PFGE). In addition to providing a genomic fingerprint PFGE can be used in conjunction with gene probing to locate specific DNA sequences of interest such as rRNA or antibiotic resistance genes. More recently the applicability of a range of PCR-basecl methods including rep-PCR, ERIC-PCR and RAP-D have been assessecl. For the investigation of antibiotic resistance recent advances in the PCR mapping of integrons coupled with direct sequencing of amplffielcl gene products has added a new dimension to our untlerstanding of the epidemiology of chromosonnlly-located resistance genes in key serotypes and phage types. The strengths ancl weaknesses of genomic'fingerprinfing will be discussed with particular reference to recent international outbreaks of Salmonella agon4 S. anatum and multiresisrant S. typhimurium DT 104 (DT 104). In relation to DT 104, the use of inregron analysis by PCR to investigate the epidemiology of multiple antibiotic resistance genes in this key phage type wiLl also be discussed.