Briefly, SOEA and SOED primers were used to amplify the whole zurR region. This was then digested with restriction enzymes XbaI and EcoRI and ligated to a similarly digested pKSV7.

Following electroporation into E. coli DH5α, the construct was then extracted and transformed into competent EGDe ΔzurR. Plasmid integration, subsequent excision, and curing were carried out as described previously (Rea et al., 2004), with continuous passaging in BHI at 30 °C. The complementation Selleckchem Rapamycin was confirmed using primers SOE X and SOE Y. BHI motility agar plates or defined media motility agar plates were made up using 0.2% agar. Tetrazolium dye was added to the growth medium to enhance visualization of bacterial growth. Twenty millilitres of the desired media was added to each plate and allowed to solidify. Overnight cultures were pelleted by centrifugation and were washed

twice in PBS prior to use. Cultures were resuspended in PBS and were stabbed into the agar using a sterile inoculating needle. All plates were maintained at room temperature and were inspected daily for culture migration. One milliliter of overnight cultures of L. monocytogenes EGDe and ΔzurR was centrifuged (2938 g for 8 min) and washed twice with PBS. The resulting pellets were fixed in a primary fixative that consisted of 2% glutaraldehyde and 2.5% paraformaldehyde in 0.165 M phosphate buffer (pH 7.3). Following primary fixation, specimens were washed in buffer, postfixed in 2% osmium Acetophenone tetroxide

find more in the same buffer, dehydrated in graded acetones, and air dried from tetramethylsilane. Samples were mounted onto stubs using double sided carbon tape. All samples were sputter coated with a thin layer of gold using a Bio-RAD Polaron Sputter Coating Unit, before being examined using a scanning electron microscope, Jeol JSM-5510. Digital electron micrographs were obtained of areas of interest. For animal assays, 8–12-week female BALB/c mice were divided into groups of five for statistical analysis. For the infection assay, overnight listerial cultures were pelleted by centrifugation, washed twice with phosphate-buffered saline (PBS), resuspended in PBS, and subsequently diluted in PBS to approximately 1.5 × 106 CFU mL−1. In vivo survival was determined by inoculating 8–12-week-old female BALB/c mice intraperitoneally (i.p.) with approximately 3 × 105 CFU in 200 μL of PBS. The mice were euthanized 3 days postinfection. Bacterial numbers in the livers and spleens were determined by homogenization of the organs, serial dilution in PBS, and subsequent plating onto BHI agar. Plates were incubated for 24 h at 37 °C before colony counts were recorded. All murine experiments received prior approval by the University ethics committee. To determine the ability of strains to survival at lethal bile concentrations, stationary phase cultures of wild-type and mutant strains were subjected to lethal levels of bovine bile (oxgall).