pneumoniae, the role of virulence factors such as CPS, and the relevance of this interaction in vivo. We have recently shown that an isogenic

CPS mutant activates host cellular inflammatory responses and that CPS might prevent this activation through blockage of bacterial uptake [13]. Moreover, Klebsiella infection increases the expression levels of Toll-like receptors 2 and 4 (TLR2 and TLR4) [14]. This increased expression of TLRs results in an enhancement of the cellular Foretinib cost response upon stimulation with Pam3CSK4 or lipopolysaccharide, TLR2 and TLR4 agonists, respectively [14]. In this study, we show for the first time that K. pneumoniae exerts a cytotoxic effect on airway epithelial cells that is associated with the presence of CPS. Methods Bacterial strains K. pneumoniae strains 52145 and 1850 are clinical isolates belonging to serotypes O1:K2 and O1:K35, respectively [15]. K. pneumoniae Selleckchem Salubrinal strain 43816 (ATCC 43816) belongs to serotype O1:K2. K. pneumoniae 52K10 is a derivative of strain 52145 which lacks CPS [16]. K. pneumoniae strains were cultured in Luria-Bertani (LB) medium at 37°C. CPS purification

and quantification Cell-bound CPS was purified by the phenol-water method [17]. Briefly, bacteria were grown in 1 l LB-broth in 2 l flasks in an orbital shaker (180 rpm) for 24 h at 37°C. Cells were removed by centrifugation and washed once with PBS. The pellet was extracted with phenol, and polysaccharides present in the aqueous phase were precipitated by adding 5 volumes of methanol plus 1% (v/v) of a saturated solution of sodium acetate in methanol. After incubation for 24 h at -20°C, the pellet was recovered by centrifugation, dissolved in distilled second water, dialysed

against water and freeze-dried. For further purification, this preparation was dispersed (final concentration 10 mg/ml) in 0.8% NaCl/0.05% NaN3/0.1 M Tris-HCl (pH 7) and digested with nucleases (50 mg/ml of DNase II type V and RNase A [Sigma Chemical Co., St. Louis, Mo.]) for 18 h at 37°C. Proteinase K was added (50 mg/ml [E. Merck, Darmstadt, Germany]), and the mixture was incubated for 1 h at 55°C and for 24 h at room temperature. The proteinase K digestion was repeated twice and the polysaccharides were precipitated as described above. The pellet was recovered by centrifugation and dissolved in distilled water. LPS was removed by ultracentrifugation (105000 × g, 16 h, 4°C) and samples were freeze-dried. The enzymatic treatment and ultracentrifugation steps were repeated once. This CPS preparation was repurified by the method described by Hirschfeld and co-workers [18]. This method is widely used to remove proteins from polysaccharide preparations. SDS-PAGE-resolved preparations were transferred to PVDF membrane which was stained with colloidal gold to visualize proteins [19]. No trace of contaminant proteins was found (data not shown).