However, many genes previously reported to be virulence associated were not up-regulated in the presence of serum.

Expression of these genes may require additional signals that were absent from our study. Alternatively, these genes may be expressed transiently in particular host niches, expressed constitutively or the proteins may be regulated at the translational level. In addition, microarray analyses are also limited in that transcripts which are unstable or have a short half-life are unlikely to be measured accurately. However, our results serve to advance our understanding A-769662 mouse of genes which may be important in pathogenesis. Genes of unknown function are over represented in the set of genes HDAC inhibitor unique to pathogenic Leptospira spp. [45], consistent with the notion that Leptospira possesses unique virulence factors. Accordingly, such genes of unknown function that are differentially regulated upon serum exposure warrant further investigation to gain a better insight into their roles in the

pathogenesis of leptospirosis. Methods Bacterial growth and conditions Pathogenic L. interrogans serovar Copenhageni strain L533, and non-pathogenic L. biflexa serovar Patoc strain L41 were grown in EMJH broth medium at 30°C under aerobic conditions. Leptospires were grown to exponential phase at an approximate density of 5-8 × 108cells/ml before harvesting by centrifugation at 8000 × g. Complement and heat-inactivated sera CYC202 molecular weight Normal guinea pig serum (NGS) (Sigma, St Louis, MO) was obtained lyophilized and stored at -80°C until use. Serum was reconstituted in 1 or 5 ml of sterile ice-cold deionized water according to the manufacturer’s instructions. To maintain selleck products consistency, the same batch of serum was used throughout. Heat-inactivated serum (HIS) was obtained by incubating NGS at 56°C for 30 min. Sera were freshly prepared before use or stored at -80°C until use. Serum was prewarmed at 37°C for 30 min before incubating with leptospires. Serum bactericidal assay Serum bactericidal

assays were performed as described previously with minor modification [38]. Pathogenic leptospires were grown to exponential phase and diluted in liquid EMJH medium to a density of 2 × 108cells/ml before use. 1 × 107 bacteria were incubated with 50% NGS in a final volume of 100 μl at 37°C for up to 2 h. HIS was used as a control. Samples were taken at different time points and viable spirochetes were enumerated by dark-field microscopy using a Petroff-Hausser counting chamber. The percentage of viable leptospires was calculated by comparison with those incubated with 50% HIS which were considered as 100% viability. The assay was performed in triplicate. The non-pathogenic, complement-sensitive L. biflexa serovar Patoc was used in parallel under the same conditions as a control for serum killing. Microarray construction Microarrays were constructed based on a revised annotation of the whole genome sequence of L.