Biofilm formation of Klebsiella pneumoniae on urethral catheters requires either type 1 or type 3 fimbriae

Abstract

Urinary catheters are standard medical devices utilized in both hospital and nursing home settings, but are associated with a high frequency of catheter-associated urinary tract infections (CAUTI). In particular, biofilm formation on the catheter surface by uropathogens such as Klebsiella pneumoniae causes severe problems. Here we demonstrate that type 1 and type 3 fimbriae expressed by K. pneumoniae enhance biofilm formation on urinary catheters in a catheterized bladder model that mirrors the physico-chemical conditions present in catheterized patients. Furthermore, we show that both fimbrial types are able to functionally compensate for each other during biofilm formation on urinary catheters. In situ monitoring of fimbrial expression revealed that neither of the two fimbrial types is expressed when cells are grown planktonically. Interestingly, during biofilm formation on catheters, both fimbrial types are expressed, suggesting that they are both important in promoting biofilm formation on catheters. Additionally, transformed into and expressed by a nonfimbriated Escherichia coli strain, both fimbrial types significantly increased biofilm formation on catheters compared with the wild-type E. coli strain. The widespread occurrence of the two fimbrial types in different species of pathogenic bacteria stresses the need for further assessment of their role during urinary tract infections.

Fig. 1

(a) Colonization of catheterized bladder model by wild type C3091 and C3091Δfim, C3091Δmrk and double mutant C3091ΔfimΔmrk. (b) Colonization of catheterized bladder model by wild type C3091 and double mutant C3091ΔfimΔmrk carrying different complementation constructs pEpi-Fos-5 (control), pEpiFosfim (type 1 fimbriae), and pEpiFosmrk (type 3 fimbriae). Each bar represents total CFU in the bladder or catheter tip and CFU per cm of catheter after 70 h of cultivation using pooled urine (M ± SE, n = 3). Statistical significant differences (P < 0.05) to wild type C3091 colonization are indicated by an asterisk.

Fig. 2

Orientation of the fim phase switch during planktonic growth and biofilm formation on urinary catheters by wild type, C3091. Lane 1, molecular size marker. Lane 2, planktonic growth. Lane 3, biofilm formation catheter tip (in the bladder). Lane 4, biofilm formation on catheter. ‘On’ denotes, that fim switch is transcribing fimA, while ‘off’ denotes no transcription of fimA.

Fig. 3

Expression of type 1 (Red) and type 3 (Green) fimbriae by individual Klebsiella pneumoniae C3091 cells grown as a biofilm on urinary tract catheters (a) or planktonically in urine (b) using type 1 fimbriae specific antibodies and type 3 fimbriae specific antibodies. Black cells are non-fimbriated cells. Note that during biofilm formation on urinary catheters each individual cell is expressing either type 1 or type 3 fimbriae not both. Scale bars denote 20 μm.

Fig. 4

Biofilm formation on urinary tract catheters by the non-fimbriated Escherichia coli strain HB101[pUC18], HB101[pCAS624] expressing type 1 fimbriae and HB101[pCAS625] expressing type 3 fimbriae, quantified by crystal violet straining after 48 h. All experiments were performed in triplicates. Means are shown and statistical calculations done by Students t-test.