At all timepoints, the wild type and the type 1 fimbriae mutant formed significantly more biomass per surface area than the two mutants lacking the ability to form type 3 fimbriae (C3091Δmrk and C3091ΔfimΔmrk) (Figure 4A). No significant differences in biomass were detected between the wild type and the type 1 fimbriae mutant in the 1-3 days old biofilms. In contrast, a highly significant difference in biomass between the wild type and the type 3 fimbriae mutant (P < 0.01) and the type

1 and type 3 fimbriae double mutant was observed at all timepoints (P < 0.01). selleck screening library Figure 4 Quantitative analysis of biofilm formation by K. pneumoniae C3091 and its isogenic fimbriae mutants at different time-points by use of the computer program COMSTAT. A. Biomass. B. Substratum coverage (1 represents total coverage). C. Average thickness of biofilm. The mean and standard errors of the means are shown. Values were calculated from analysis of a minimum of seven images. Also the substratum coverage

was significantly reduced for the type 3 fimbriae mutants PI3K inhibitor in the 1-3 days old biofilms (Figure 4B). Both the type 3 fimbriae mutant and the type 1 and 3 fimbriae double mutant exhibited a much lower substratum coverage than the wild type (P < 0.01), whereas there was no significant difference between the wild type and the type 1 fimbriae mutant. The average thickness of the 1-3 days old biofilms formed by the type 3 fimbriae mutant and the type 1 and 3 fimbriae mutant was also significantly lower than for the wild type (Figure 4C) (P < 0.01), while

there was no significant difference between the wild type and the type 1 fimbriae mutant. Thus type 3 fimbriae do not only mediate cell-surface attachment to the substratum, but are also important for cell-cell adherence. Complementation by type 3 fimbriae restores biofilm formation of the mutant To verify that the attenuated biofilm formation of the type 3 fimbriae mutants was due to abolishment of type 3 fimbriae expression and not polar effects of the mutation, the type 3 fimbriae mutant was transformed with pCAS630 containing the C3091 mrk gene cluster [19]. In contrast to the type 3 fimbriae mutant, the complemented mutant exhibited pronounced biofilm formation OSBPL9 confirming the significant role of type 3 fimbriae in K. pneumoniae biofilm formation (Figure 5). In fact, the biofilm formation was even more prominent than for the wild type strain, likely due to enhanced type 3 fimbriae expression from the plasmid vector. Figure 5 Comparison of biofilm formation by the wild type, type 3 fimbriae mutant, and the type 3 fimbriae mutant transformed with pCAS630 containing the type 3 fimbriae gene cluster. Biofilm formation was examined in three independent experiments with similar results. Box sides 230 μm × 230 μm. Type 1 fimbriae expression is down-regulated in K. pneumoniae biofilms Expression of K.