The modified FAB medium was supplemented with glucose (100 mg l-1) as carbon source and isopropyl-thio-beta-galactoside (IPTG; 12 mg l-1) to ensure expression of fluorescent proteins from the PA1/04/03 promotor. The flow system was assembled and prepared as described previously this website [24]. A microscope cover slip of borosilicate (Knittel 24 × 50 mm st1; Knittel Gläser) was used as substratum. The flow chambers were inoculated by injecting approximately 2 × 106 cells, into each flow chamber

with a small syringe. After inoculation, the flow chambers were left without flow for 1 h, and medium flow (0.2 or 0.8 mm s-1 corresponding to laminar flow and Re numbers of 0.3 and 1.3,

respectively) was started using a Watson Marlow 205 S peristaltic pump and the system was incubated at 30°C. Microscopy and image acquisition Biofilm formation was monitored by CLSM four, 24, 48, and 72 hours after inoculation. Microscopic observations and image acquisitions were performed with a Zeiss LSM 510 CLSM (Carl Zeiss, Jena, Germany) using a 40 ×/1.3 oil objective. C646 The microscope was equipped with lasers, detectors and filter sets for detecting CFP and YFP fluorescence. Simulated three-dimensional images were generated using the IMARIS software package (Bitplane AG, Zürich, Switzerland). Quantification of biofilm formation and statistical analysis For quantitative analysis of the biofilms, CLSM images were analysed by the computer program Rutecarpine COMSTAT [25]. The total amount of biomass on the surface, the relative substratum coverage

and the average thickness of the biofilm were calculated. Differences between the wild type and each mutant in the three parameters were compared by using a two-tailed independent t-test. P values below 0.05 were considered to be statistically significant. Fimbrial switch orientation assay A modification of a previously described method was used to determine the orientation of the fim-switch in K. pneumoniae biofilms [18, 26]. Biofilm Selleckchem NSC 683864 samples were obtained by aspiration of the biofilm from individual flow cell channels by use of a syringe. All inoculum and biofilm samples were boiled for 5 min in PBS immediately after collection and then kept at -20°C until use. After thawing, the samples were boiled for 5 min, centrifuged at 12,000 g for 15 min and 2 μl of the supernatant used as template for PCR. Primers CAS168 and CAS169 (Table 1) were used to amplify an 817 bp region containing the fim-switch by use of the Expand High Fidelity PCR System (Roche).