title: Differential phenotypic diversity among epidemic-spanning Salmonella enterica serovar enteritidis isolates from humans or animals.
abstract: Nontyphoidal salmonellae are major causes of food-borne disease worldwide. In Uruguay, Salmonella enterica serovar Enteritidis was the most commonly isolated serovar throughout the last decade, with a marked epidemic period between 1995 and 2004. In a previous study, we conducted comparative genomics of 29 epidemic-spanning S. Enteritidis field isolates, and here we evaluated the pathogenic potential of the same set of isolates using several phenotypic assays. The sample included 15 isolates from human gastroenteritis, 5 from invasive disease, and 9 from nonhuman sources. Contrary to the genetic homogeneity previously observed, we found great phenotypic variability among these isolates. One-third of them were defective in at least one assay, namely, 10 isolates were defective in motility, 8 in invasion of Caco-2 cells, and 10 in survival in egg albumen. Twelve isolates were tested for invasiveness in 3-day-old chickens, and five of these were significantly less invasive than the reference strain. The two oldest preepidemic isolates were reduced in fitness in all assays, providing a plausible explanation for the previous negligible incidence of S. Enteritidis in Uruguay and supporting the view that the introduction or emergence of a more virulent strain was responsible for the marked rise of this serovar. Further, we found differences in fitness among the isolates which depended on the source of isolation. A total of 1 out of 14 isolates from human gastroenteritis, but 6 out of 13 isolates from other sources, was impaired in at least two assays, suggesting enhanced fitness among strains able to cause intestinal disease in humans.
authors.affiliation: Department of Biotechnology, Instituto de Higiene, School of Medicine, Avda. A. Navarro 3051, CP 11600, Montevideo, Uruguay.
authors.forename: Lucía
authors.initials: L
authors.lastname: Yim
authors.forename: Laura
authors.initials: L
authors.lastname: Betancor
authors.forename: Arací
authors.initials: A
authors.lastname: Martinez
authors.forename: Gerardo
authors.initials: G
authors.lastname: Giossa
authors.forename: Clare
authors.initials: C
authors.lastname: Bryant
authors.forename: Duncan
authors.initials: D
authors.lastname: Maskell
authors.forename: Jose A
authors.initials: JA
authors.lastname: Chabalgoity
mesh_terms: D000818:Animals; D018938:Caco-2 Cells; D002645:Chickens; D004195:Disease Models, Animal; D004531:Eggs / Q000382:microbiology; D004847:Epithelial Cells / Q000382:microbiology; D006801:Humans; D008124:Locomotion; D050296:Microbial Viability; D011201:Poultry Diseases / Q000382:microbiology / Q000473:pathology; D012480:Salmonella Infections / Q000453:epidemiology* / Q000382:microbiology*; D012481:Salmonella Infections, Animal / Q000453:epidemiology* / Q000382:microbiology*; D012477:Salmonella enteritidis / Q000145:classification* / Q000235:genetics / Q000302:isolation & purification / Q000502:physiology*; D014583:Uruguay; D014774:Virulence
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