koseri M546 (lane 2), C. koseri M546mrk (lane 3), E. coli ECOR15 (lane 4), E. coli ECOR15mrk (lane 5), K. oxytoca M126 (lane 6), K. oxytoca M126mrk (lane 7), K. pneumoniae M692 (lane 8) and K. pneumoniae M692mrk (lane 9) were acid boiled prior to loading. Molecular see more size markers are indicated in lane 1. The Type 3 fimbriae major subunit, MrkA, was only observed in the wild-type strains and not in the mrk deletion mutants. The arrow indicates the ~15 kDa band

corresponding to MrkA. Figure 4 Phase contrast microscopy illustrating MR/K agglutination. Parental wild-type strains C. koseri M546, E. coli ECOR15, K. oxytoca M126, K. pneumoniae M692 and C. freundii M46 demonstrated strong agglutination of tannic acid treated human erythrocytes, while their corresponding mrk deletion mutants, M546mrk, ECOR15mrk, M126mrk, M692mrk and M46mrk were negative for agglutination. Figure 5 Immunogold electron microscopy demonstrating expression of type 3 fimbriae in E. coli ECOR15 and C. koseri M546. Expression of type 3 fimbriae at the cell surface was demonstrated by abundant labelling with anti-type 3 fimbriae-gold particles. In contrast, the deletion mutants, E. coli ECOR15mrk and C. koseri M546mrk were virtually devoid of gold labelling. Scale bar represents 1 μm. Type

3 fimbriae are strongly associated with biofilm formation The thirteen sets of isogenic wild-type and mrk deletion strains generated above were examined for their ability to produce a biofilm following growth in M9 minimal medium (TPCA-1 price containing 0.2% glucose) under dynamic culture conditions. Strong biofilm growth was observed from all wild-type selleck compound strains except C. freundii M46. In contrast, deletion of the mrk gene cluster caused a significant

reduction in Tau-protein kinase biofilm growth (p < 0.0001) in all strains except E. coli M184 (Fig. 6). Similar results were also observed following growth in synthetic urine (data not shown). Thus, type 3 fimbriae contribute significantly to biofilm formation when expressed in E. coli, K. pneumoniae, K. oxytoca and C. koseri. Figure 6 Biofilm formation by wild-type and isogenic mrk deletion strains. Strains were grown at 37°C under shaking conditions for 16 h in PVC microtitre plates containing M9 minimal medium, washed to remove unbound cells and stained with 0.1% crystal violet. Biofilm formation was quantified by resuspending adherent cells in ethanol-acetate (80:20) and measuring the absorbance at 595 nm. Shown are the results for E. coli MS2027, M184, ECOR15 and, ECOR28, K. pneumoniae M20, M124, M446, M542 and, M692, K. oxytoca M126 and, M239, C. koseri M546 and C. freundii M46 and their respective mrk deletion mutants. Discussion Type 3 fimbriae are adhesive organelles produced by a range of Gram-negative pathogens that cause CAUTI. Here we show that type 3 fimbriae (mrkABCD) genes from 33 CAUTI isolates representing C. freundii, C. koseri, E. coli, K. oxytoca and K. pneumoniae cluster into five well-supported clades on the basis of nucleotide sequence.