title: Aeromonas salmonicida Type I pilus system contributes to host colonization but not invasion.
abstract: The host-adherence strategies employed by Aeromonas salmonicida subsp, salmonicida, the etiological agent of an infectious bacteremia of salmonids, are poorly understood. In addition to the outer protein coat or S-layer, A. salmonicida has both Type I and Type IV pili loci. The A. salmonicida Type I or Fim pilus is encoded by an operon with genes for a chaperone, an usher, and 3 pilus subunits and is predicted to be similar to the Pap fimbriae of uropathogenic Escherichia coli, which are considered significant virulence factors. A Fim-deficient strain of A. salmonicida strain A449, delta fim, was created by deleting this operon. Virulence of delta fim was unchanged in direct live challenges of Atlantic salmon Salmo salar L., a natural host for A. salmonicida. A measure of clinically inapparent (covert) infections suggested Fim was required to establish or maintain a covert infection. This was confirmed by an ex vivo adherence and invasion assay using freshly excised salmon gastrointestinal (GI) tract, which showed that, compared to the parental strain, the ability of the isogenic delta fim mutant strain to adhere to the salmon GI tract was reduced but, once adhered, its ability to invade was unchanged. Thus the Fim pilus functions as an adhesin in A. salmonicida and the presence of a functional Fim improved the efficiency of A. salmonicida infection of Atlantic salmon.
authors.affiliation: National Research Council of Canada Institute for Marine Biosciences, 1411 Oxford Street, Halifax, Nova Scotia B3H 3Z1, Canada. adacanay@nsac.ca
authors.forename: Andrew
authors.initials: A
authors.lastname: Dacanay
authors.forename: Jessica M
authors.initials: JM
authors.lastname: Boyd
authors.forename: Mark D
authors.initials: MD
authors.lastname: Fast
authors.forename: Leah C
authors.initials: LC
authors.lastname: Knickle
authors.forename: Michael E
authors.initials: ME
authors.lastname: Reith
mesh_terms: D048409:Aeromonas salmonicida / Q000502:physiology*; D000818:Animals; D010861:Fimbriae, Bacterial / Q000502:physiology*; D005393:Fish Diseases / Q000382:microbiology*; D016905:Gram-Negative Bacterial Infections / Q000382:microbiology / Q000662:veterinary*; D020317:Salmo salar