title: A contingency locus in prfA in a Listeria monocytogenes subgroup allows reactivation of the PrfA virulence regulator during infection in mice.
abstract: A nonhemolytic Listeria monocytogenes strain isolated from a fish processing plant was avirulent in a plaque-forming assay and in a subcutaneous mouse virulence assay. However, it showed 60% lethality (9/15 mice) when 10⁹ CFU were intraperitoneally injected into mice. Hemolytic L. monocytogenes bacteria were recovered from liver and spleen of the deceased mice, and the pulsed-field gel electrophoresis patterns were indistinguishable for the nonhemolytic and the hemolytic isolates. Sequencing of prfA from the nonhemolytic strain revealed a duplication of 7 bp in the helix-turn-helix region, resulting in a truncated PrfA protein. We propose that the direct repeat of 7 bp causes a reversible inactivation of prfA and that slipped-strand mispairing regulates the phase variation in hemolytic activity and virulence. Nonhemolytic L. monocytogenes strains with identical duplications in prfA were isolated from several sources in France, as well as in Norway, suggesting that the reversible inactivation described in this study is not an isolated event.
authors: Department of Food Safety and Infection Biology, Norwegian School of Veterinary Science, P.O. Box 8146 Dep., N-0033 Oslo, Norway. toril.lindback@nvh.no
authors: Toril
authors: T
authors: Lindbäck
authors: Indira
authors: I
authors: Secic
authors: Liv Marit
authors: LM
authors: Rørvik
mesh_terms: D000818:Animals; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D015373:Bacterial Typing Techniques; D004269:DNA, Bacterial / Q000737:chemistry / Q000235:genetics; D004195:Disease Models, Animal; D016521:Electrophoresis, Gel, Pulsed-Field; D019649:Food Industry; D005516:Food Microbiology; D005838:Genotype; D006460:Hemolysin Proteins / Q000378:metabolism; D008089:Listeria monocytogenes / Q000145:classification / Q000235:genetics / Q000302:isolation & purification / Q000472:pathogenicity*; D008088:Listeriosis / Q000382:microbiology* / Q000401:mortality; D008099:Liver / Q000382:microbiology; D051379:Mice; D008969:Molecular Sequence Data; D058889:Molecular Typing; D009664:Norway; D010454:Peptide Termination Factors / Q000235:genetics / Q000378:metabolism*; D012091:Repetitive Sequences, Nucleic Acid; D017422:Sequence Analysis, DNA; D013154:Spleen / Q000382:microbiology; D016019:Survival Analysis; D014774:Virulence; D037521:Virulence Factors / Q000235:genetics / Q000378:metabolism*
chemical_list: D001426:Bacterial Proteins; D004269:DNA, Bacterial; D006460:Hemolysin Proteins; D010454:Peptide Termination Factors; C545356:PrfA protein, Listeria monocytogenes; D037521:Virulence Factors