| Summary: | <p>Abstract</p> <p>Background</p> <p>Several strain-specific <it>Klebsiella pneumoniae</it> 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 <it>met56</it> tRNA gene of <it>K. pneumoniae</it> KR116, a bloodstream isolate from a patient with pneumonia and neutropenic sepsis.</p> <p>Results</p> <p>The 14.0 kb KpGI-5 island exhibited a genome-anomalous G + C content, possessed near-perfect 46 bp direct repeats, encoded a γ<sub>1</sub>-chaperone/usher fimbrial cluster (<it>fim2</it>) and harboured seven other predicted genes of unknown function. Transcriptional analysis demonstrated expression of three <it>fim2</it> genes, and suggested that the <it>fim2A-fim2K</it> cluster comprised an operon. As fimbrial systems are frequently implicated in pathogenesis, we examined the role of <it>fim2</it> by analysing KR2107, a streptomycin-resistant derivative of KR116, and three isogenic mutants (Δ<it>fim</it>, Δ<it>fim2</it> and Δ<it>fim</it>Δ<it>fim2</it>) 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 <it>fim2</it> 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∆<it>fim2</it>, KR2107∆<it>fim</it> and KR2107∆<it>fim</it>∆<it>fim2</it> (least virulent). Thus, despite lack of statistical evidence there was a suggestion that <it>fim</it> and <it>fim2</it> contribute additively to virulence in these murine infection models. However, further studies would be necessary to substantiate this hypothesis.</p> <p>Conclusion</p> <p>Although <it>fim2</it> was present in 13% of <it>Klebsiella</it> spp. strains investigated, no obvious <it>in vitro</it> or <it>in vivo</it> 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 <it>fim2</it> has the potential to contribute beneficially to pathogenesis and/or environmental persistence of <it>Klebsiella</it> strains, at least under specific yet-to-be identified conditions.</p>
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