MAPK pathways are involved in the signal transduction of a wide variety of extracellular stimuli

efflux pump blocker. Efflux pump inhibitors had no intrinsic antibacterial activity against wild type strain at the concentration used in the experiments. Osmotic, bile, chlorhexidine challenge assays Various stress assays were performed 9720791 as described previously. Briefly, K. pneumoniae NTUH-K2044 and NTUHK2044DcpxAR were grown to mid-exponential phase, cultures were spread plated onto LB agar plates containing different concentrations of NaCl, bile and chlorhexidine respectively. The results are expressed as the ratio of the number of colony forming units obtained from LB cultures containing different concentrations of NaCl, bile and chlorhexidine to the number of colony forming units obtained from control cultures. These experiments were performed at least three times. Oxidative stress sensitivity assay In this susceptibility test, small Whatman 3 MM paper disks was impregnated with different amount of H2O2 and later air dried as reported before. The K. pneumoniae NTUH-K2044 and NTUH-K2044DcpxAR were grown to the mid-log phase and was uniformly spread over an LB agar plate. Next, filter paper disks impregnated with specific concentrations of H2O2 was placed at the centre on to the agar surface. The culture was then incubated at 37uC for 1224 hours. The diameter of a zone of inhibition was measured which is a qualitative measure of the inhibitory activity of a compound. The data represents the distances from the edge of the disks to the end of the clear zone, where growth begins. Each experiment was repeated at least three times. String and Precipitation test for Hypermucoviscosity The NTUH-K2044 and NTUH-K2044DcpxAR was streaked onto LB agar plates and incubated at 37uC overnight. A standard bacteriologic loop was used to stretch a mucoviscous string from the colony. Hypermucoviscosity was defined by the formation of viscous strings.5 mm in length when a loop was used to stretch the colony on agar plate which was considered the positive string test. The strains to be tested were cultured overnight in LB broth at 37uC and subjected to centrifugation at 1,0006g for 5 min to check reduction in mucoidy. For exopolysaccharide analysis, cells were grown to late log phase in shaking culture and stained with crystal violet followed by treatment with 20% copper sulphate solution. Samples were visualized using an Olympus microscope work station. Capsular polysaccharides were extracted from overnight bacterial suspensions adjusted to,108 cells per ml with Zwittergent 314 detergent. The amount of uronic acid was then measured according to the method described previously. Each experiment was performed in triplicate. Antibiotic susceptibility testing Strains in this study were examined for resistance to nalidixic acid: NA30, colistin: CL30, enrofloxacin: EX10, polymyxin B: PB300, ciprofloxacin: CF5, azithromycin: AT15, erythromycin: E15, tetracycline: T30, rifampicin: R5, trimethoprim: TR5, kanamycin: K30, streptomycin: S10, tobramycin: TB10, clindamycin: CD2, spectinomycin: S100, UNC0642 imipenem: I10, ampicillin: A10, ertapenem: ETP10, piperacillin: PC100, ticarcillin: TI75, ceftazidime: CA30, chloramphenicol: C30, ceftriaxone: CI30, cefepime: CPM30 and carbencillin: CB100 by using commercial discs as described previously according to the interpretation criteria recommended by Clinical and Laboratory Standards Institute CLSI. MIC ” of antibiotics was tested using E-strips. Interpretation was done as per the criteria approved by CLSI. E. coli ATCC 25922 was u