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Background  Several strain-specific  Klebsiella pneumoniae  virulence determinants have been described, though these have almost exclusively been linked with hypervirulent liver abscess-associated strains. Through PCR interrogation of integration hotspots, chromosome walking, island-tagging and fosmid-based marker rescue we captured and sequenced KpGI-5, a novel genomic island integrated into the  met56  tRNA gene of  K. pneumoniae  KR116, a bloodstream isolate from a patient with pneumonia and neutropenic sepsis.    Results  The 14.0 kb KpGI-5 island exhibited a genome-anomalous G + C content, possessed near-perfect 46 bp direct repeats, encoded a γ 1 -chaperone/usher fimbrial cluster ( fim2 ) and harboured seven other predicted genes of unknown function. Transcriptional analysis demonstrated expression of three  fim2  genes, and suggested that the  fim2A-fim2K  cluster comprised an operon. As fimbrial systems are frequently implicated in pathogenesis, we examined the role of  fim2  by analysing KR2107, a streptomycin-resistant derivative of KR116, and three isogenic mutants (Δ fim , Δ fim2  and Δ fim Δ fim2 ) using biofilm assays, human cell adhesion assays and pair-wise competition-based murine models of intestinal colonization, lung infection and ascending urinary tract infection. Although no statistically significant role for  fim2  was demonstrable, liver and kidney CFU counts for lung and urinary tract infection models, respectively, hinted at an ordered gradation of virulence: KR2107 (most virulent), KR2107∆ fim2 , KR2107∆ fim  and KR2107∆ fim ∆ fim2  (least virulent). Thus, despite lack of statistical evidence there was a suggestion that  fim  and  fim2  contribute additively to virulence in these murine infection models. However, further studies would be necessary to substantiate this hypothesis.    Conclusion  Although  fim2  was present in 13% of  Klebsiella  spp. strains investigated, no obvious  in vitro  or  in vivo  role for the locus was identified, although there were subtle hints of involvement in urovirulence and bacterial dissemination from the respiratory tract. Based on our findings and on parallels with other fimbrial systems, we propose that  fim2  has the potential to contribute beneficially to pathogenesis and/or environmental persistence of  Klebsiella  strains, at least under specific yet-to-be identified conditions.

bmc microbiology

Characterization of a novel chaperone/usher fimbrial operon present on KpGI-5, a methionine tRNA gene-associated genomic island in Klebsiella pneumoniae