Bacteriophage λ concatemers were used as DNA size markers. DNA restriction patterns of scanned BVD-523 molecular weight gel pictures were interpreted following cluster analysis with Fingerprinting II version 3.0 software (Bio-Rad) using the unweighted pair-group method with arithmetic averages (UPGMA). The Dice correlation coefficient was used with a 1.2% position tolerance to analyse the similarities of the banding patterns. Only bands larger than 48 Kb were considered for the analysis. Isolates showing more than three DNA fragment differences and a similarity of <80% were considered to represent different PFGE types, while isolates with less than three fragment differences and a similarity of >80% were

considered as belonging to the same PFGE subtype, following the criteria for genetic characterization using PFGE described in the literature [23, 46, 47]. A. baumannii RUH875 and

RUH134 were used as reference strains representative of the European clonal lineages I and II, respectively this website [20, 48]. Biofilm formation assays and determination of EPS production Biofilm formation in microtiter plates was determined as described [49]. Bacterial cells were grown overnight in microtiter plates (0.2 ml) either at 30°C or 37°C. Bacterial growth in the liquid culture was determined by optical density at 600 nm (OD600 nm) and the liquid culture was removed. Microtiter plates were washed with 0.1 M phosphate buffer (pH 7.0), and the biofilm cells attached to the microtiter plate wells were stained for 20 min with 1% crystal violet (CV) in ethanol, washed, and dried. Crystal violet staining was visually assessed and the microtiter plates were scanned. For semi-quantitative determination of biofilms, CV-stained cells were resuspended in either 0.2

ml of 70% ethanol. The absorbance at 600 nm (Abs600 nm) of the resuspended CV was determined and normalized to the OD600 nm of the corresponding grown cell density: this value corresponds to the http://www.selleck.co.jp/products/AP24534.html “”adhesion units”". To test biofilm sensitivity to cellulase, bacterial cultures were grown in the presence of cellulase from Trichoderma reesei ATCC 26921 (5 mg/ml, 700 U/ml, Sigma). For detection of cellulose production by binding to the fluorescent dye Calcofluor (CF), bacteria were grown overnight in a microtiter plate, and the cultures were spotted, using a replicator, on solid media to which 0.005% Calcofluor (for CF medium) was added after autoclaving. Bacteria were grown for 18-20 h at 30°C; staining was better detected after 24-48 h of additional incubation at 4°C. SDS-PAGE analysis of membrane proteins A. baumannii cultures (100 ml) were grown in defined M9 medium, supplemented with 0.02% peptone and 0.01% yeast extract, to which 0.2% glucose was added as main carbon source (M9Glu/sup, [27]). Cultures were grown at 30°C up to 0.1 OD600 nm prior to addition of 0.125 μg/ml imipenem (1/4 the MIC). Both control and treated cultures were harvested 3 hours after imipenem addition, at an OD600 nm >1.0.