Media was free of bacteria throughout the entire experiment, suggesting efficient killing of extracellular bacteria (data not shown). At the end of experiment, after 8 hours post-exposure to antibiotics, intracellular B. mallei CFUs were negligible from cell lysates. Similar results were obtained with lower antibiotics concentration 10 × MIC and lower MOI, 12:1 (data not shown). The lactate dehydrogenase (LDH) cytotoxicity assay was performed during bacterial invasion assays to monitor cytotoxic

effects of bacteria on J774A.1 macrophages. Throughout the assay LDH levels were below 20%. Cytotoxicity was observed at 8 h in ceftazidime treated macrophages, reaching 25.7% which may have contributed to the decrease in recoverable intracellular bacteria in this treatment. Possible cytotoxic effects of antibiotics alone was ACP-196 tested in separate experiments for up to 24 h, including concentrations higher than that tested, showing no selleck inhibitor significant LDH levels (data not shown). Figure 3 Antibiotic mediated intracellular killing of B. mallei infected J774A.1 murine macrophages. Bacteria were added at an MOI of 25:1 and incubated for 2 hours at 37°C with 5% CO2 followed by incubation with 100 × MIC levofloxacin (black bars), ceftazidime (white bars) or media only (crossed bars). Media in control

wells contained 250 μg/ml kanamycin for first 2 h postinfection and 100 μg/ml kanamycin for the rest of the assay to prevent the growth of extracellular bacteria. At 2, 4 and 8 h post treatment, cells were washed and Cyclic nucleotide phosphodiesterase lysed with 0.1% Triton X-100, followed by serial 10-fold dilutions plated on LBG plates and incubated at 37°C for 2 days for CFUs determination. Experiment performed twice in triplicate. Errors bars represent mean ± SEM. * P < 0.05 significant difference between time 0 and all time points in levofloxacin treatment, ** P < 0.01 significant difference between time 0 and all time points in ceftazidime treatment. Discussion Limited data of in vitro antibiotic susceptibilities to strains of B. mallei has been published. The recommendations for treatments of glanders are largely based on knowledge of pathogenesis of melioidosis,

a human disease caused by a closely related species B. pseudomallei. Currently, ceftazidime is the first antibiotic of choice for treatment of acute melioidosis [14]. The previously established MICs of 16 different antimicrobials evaluated against both species showed most strains susceptible to ceftazidime, ciprofloxacin, imipenem, and doxycycline [8]. Although B. mallei has a susceptibility profile similar to B. pseudomallei, the MICs are usually lower in case of B. mallei [15]. Due to emergence of resistant strains and cases of disparity between in vitro susceptibility and clinical outcome of the treatments for melioidosis, the development of effective treatments has been Proteasome inhibitor difficult [10, 16, 17]. Both species, B. mallei and B.