title: Molecular characterization of "inconsistent" variants of Salmonella Typhimurium isolated in Italy.
abstract: Salmonella 4,[5],12:i:- is a variant of Salmonella Typhimurium, which lacks the expression of phase-2 flagellar antigen, generally associated with the deletion of the fljB gene. Additional mechanisms involving the fljAB operon ( fljA, fljB, and hin genes) lead to the lack of expression of phase-2 flagellar antigens also in Salmonella strains harboring the fljB gene. For 20 S. 4,[5],12:i:- strains, defined as "inconsistent" Salmonella Typhimurium variants since they had phenotypically behaved as monophasic, even though the fljB gene was conserved, the fljAB operon was characterized in order to explain the ineffective expression of the phase-2 flagellar antigen. The monophasic phenotype for a first group of strains (9) was likely due to the absence of the hin gene, leading to the inhibited switch between the expression of phase-1 and phase-2 flagellar genes. For a second group of strains (5), the monophasic phenotype could be attributed to nonconservative point mutations identified in fljA and hin genes, which could hamper the proper expression of invertase gene and the fljA, acting as repressor of the phase-1 flagellar gene. Finally, for a last group of inconsistent strains (6), a plausible reason for their monophasic phenotype was not found, since the genes involved in the expression of phase-2 flagellar antigen were fully conserved. Moreover, the collection of inconsistent Salmonella Typhimurium isolates investigated were characterized by distinct molecular profiles, as demonstrated by multiple-locus variable-number tandem repeat analysis, and phenotype variability, as demonstrated by phage-typing. This study highlights the usefulness of investigating the entire fljAB operon when a definitive identification of the monophasic or biphasic status of Salmonella Typhimurium strains is needed (for instance, in the context of epidemiological investigations aimed to identify the relatedness among strains).
authors.affiliation: 1 World Organization for Animal Health (OIE), National Reference Laboratory for Salmonella , Istituto Zooprofilattico Sperimentale delle Venezie, Legnaro (Padova), Italy .
authors.forename: Lisa
authors.initials: L
authors.lastname: Barco
authors.forename: Alessandra
authors.initials: A
authors.lastname: Longo
authors.forename: Antonia Anna
authors.initials: AA
authors.lastname: Lettini
authors.forename: Enzo
authors.initials: E
authors.lastname: Cortini
authors.forename: Cristina
authors.initials: C
authors.lastname: Saccardin
authors.forename: Claudio
authors.initials: C
authors.lastname: Minorello
authors.forename: John Elmerdahl
authors.initials: JE
authors.lastname: Olsen
authors.forename: Antonia
authors.initials: A
authors.lastname: Ricci
mesh_terms: D000818:Animals; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D001434:Bacteriophage Typing; D005243:Feces / Q000382:microbiology; D005408:Flagellin / Q000235:genetics / Q000378:metabolism*; D020869:Gene Expression Profiling; D015964:Gene Expression Regulation, Bacterial; D014644:Genetic Variation; D006801:Humans; D007558:Italy; D008460:Meat / Q000382:microbiology; D008954:Models, Biological; D058889:Molecular Typing; D058885:Multilocus Sequence Typing; D009154:Mutation; D009876:Operon; D012097:Repressor Proteins / Q000235:genetics / Q000378:metabolism*; D015203:Reproducibility of Results; D012478:Salmonella Food Poisoning / Q000382:microbiology; D012486:Salmonella typhimurium / Q000145:classification / Q000235:genetics / Q000302:isolation & purification* / Q000378:metabolism; D013045:Species Specificity
chemical_list: D001426:Bacterial Proteins; C079830:FljA protein, Salmonella; C094427:FljB protein, Salmonella; D012097:Repressor Proteins; D005408:Flagellin