title: Limited genetic diversity in Salmonella enterica serovar Enteritidis PT13.
abstract: BACKGROUND
  Salmonella enterica serovar Enteritidis has emerged as a significant foodborne pathogen throughout the world and is commonly characterized by phage typing. In Canada phage types (PT) 4, 8 and 13 predominate and in 2005 a large foodborne PT13 outbreak occurred in the province of Ontario. The ability to link strains during this outbreak was difficult due to the apparent clonality of PT13 isolates in Canada, as there was a single dominant pulsed-field gel electrophoresis (PFGE) profile amongst epidemiologically linked human and food isolates as well as concurrent sporadic strains. The aim of this study was to perform comparative genomic hybridization (CGH), DNA sequence-based typing (SBT) genomic analyses, plasmid analyses, and automated repetitive sequence-based PCR (rep-PCR) to identify epidemiologically significant traits capable of subtyping S. Enteritidis PT13.
  
  
  RESULTS
  CGH using an oligonucleotide array based upon chromosomal coding sequences of S. enterica serovar Typhimurium strain LT2 and the Salmonella genomic island 1 successfully determined major genetic differences between S. Typhimurium and S. Enteritidis PT13, but no significant strain-to-strain differences were observed between S. Enteritidis PT13 isolates. Individual loci (safA and fliC) that were identified as potentially divergent in the CGH data set were sequenced in a panel of S. Enteritidis strains, and no differences were detected between the PT13 strains. Additional sequence-based typing was performed at the fimA, mdh, manB, cyaA, citT, caiC, dmsA, ratA and STM0660 loci. Similarly, no diversity was observed amongst PT13 strains. Variation in plasmid content between PT13 strains was observed, but macrorestriction with BglII did not identify further differences. Automated rep-PCR patterns were variable between serovars, but S. Enteritidis PT13 strains could not be differentiated.
  
  
  CONCLUSIONS
  None of the methods identified any significant variation between PT13 strains. Greater than 11,300 base pairs of sequence for each of seven S. Enteritidis PT13 strains were analyzed without detecting a single polymorphic site, although diversity between different phage types of S. Enteritidis was observed. These data suggest that Canadian S. Enteritidis PT13 strains are highly related genetically.
authors.affiliation: National Microbiology Laboratory, Public Health Agency of Canada, Winnipeg, MB, Canada. Adam_Olson@phac-aspc.gc.ca
authors.forename: Adam B
authors.initials: AB
authors.lastname: Olson
authors.forename: Ashleigh K
authors.initials: AK
authors.lastname: Andrysiak
authors.forename: Dobryan M
authors.initials: DM
authors.lastname: Tracz
authors.forename: Jean
authors.initials: J
authors.lastname: Guard-Bouldin
authors.forename: Walter
authors.initials: W
authors.lastname: Demczuk
authors.forename: Lai-King
authors.initials: LK
authors.lastname: Ng
authors.forename: Anne
authors.initials: A
authors.lastname: Maki
authors.forename: Frances
authors.initials: F
authors.lastname: Jamieson
authors.forename: Matthew W
authors.initials: MW
authors.lastname: Gilmour
mesh_terms: D000818:Animals; D002170:Canada / Q000453:epidemiology; D004269:DNA, Bacterial / Q000737:chemistry / Q000235:genetics; D004196:Disease Outbreaks; D016521:Electrophoresis, Gel, Pulsed-Field; D005516:Food Microbiology; D014644:Genetic Variation; D006801:Humans; D020411:Oligonucleotide Array Sequence Analysis; D016133:Polymerase Chain Reaction; D012150:Polymorphism, Restriction Fragment Length; D011200:Poultry; D011201:Poultry Diseases / Q000382:microbiology; D012189:Retrospective Studies; D012478:Salmonella Food Poisoning / Q000453:epidemiology / Q000382:microbiology*; D012480:Salmonella Infections / Q000453:epidemiology / Q000382:microbiology*; D012477:Salmonella enteritidis / Q000145:classification / Q000235:genetics*
chemical_list: D004269:DNA, Bacterial