Infected U937 cells were incubated at 37°C in 5% CO2 for 2 h. Non-adherent bacteria were removed by washing gently 3 times with 1 ml of PBS. The U937 cells were lysed with 1 ml of 0.1% Triton X-100 (Sigma), and the cell lysates serially diluted in PBS and spread
plated on Ashdown agar to obtain the bacterial count. Colony morphology was observed . The selleck inhibitor percentage of bacteria that were cell-associated was calculated by (number of associated bacteria × 100)/number of bacteria in the inoculum. The experiment was performed in duplicate for 2 independent experiments. Intracellular survival and multiplication of B. pseudomallei in human macrophages were determined at a series of time points following the initial selleck chemicals llc co-culture described above of differentiated U937 with B. pseudomallei for 2 h. Following removal of extracellular bacteria and 10058-F4 nmr washing 3 times with PBS, medium
containing 250 μg/ml kanamycin (Invitrogen) was added and incubated for a further 2 h (4 h time point). New medium containing 20 μg/ml kanamycin was then added to inhibit overgrowth by any remaining extracellular bacteria at further time points. Intracellular bacteria were determined at 4, 6 and 8 h after initial inoculation. Infected cells were washed, lysed and plated as above. Intracellular survival and multiplication of B. pseudomallei based on counts from cell lysates were presented. Percent intracellular bacteria was calculated by (number of intracellular bacteria at 4 h) × 100/number of bacteria in the inoculum. Percent intracellular replication was calculated by (number of intracellular bacteria at 6 or 8 h × 100)/number of intracellular bacteria at 4 h. The experiment was performed in
duplicate for 2 independent experiments. Growth in acid conditions B. pseudomallei from an overnight culture on Ashdown agar was suspended in PBS and adjusted using OD at 600 nm to a concentration of 1 × 106 CFU/ml in PBS. Thirty microlitres of bacterial suspension Urease was inoculated into 3 ml of Luria-Bertani (LB) broth at a pH 4.0, 4.5 or 5.0. The broth was adjusted to acid pH with HCl. Growth in LB broth at pH 7.0 was used as a control. The culture was incubated at 37°C in air with shaking at 200 rpm. At 1, 3, 6, 12 and 24 h time intervals, the culture was aliquoted and viability and growth determined by serial dilution and plating on Ashdown agar. Susceptibility of B. pseudomallei to reactive oxygen intermediates (ROI) The sensitivity of B. pseudomallei to reactive oxygen intermediates was determined by growth on oxidant agar plates and in broth containing H2O2. Assays on agar plates were performed as described previously , with some modifications. Briefly, an overnight culture of B. pseudomallei harvested from Ashdown agar was suspended in PBS and the bacterial concentration adjusted using OD at 600 nm. A serial dilution of the inoculum was spread plated onto Ashdown agar to confirm the bacterial count and colony morphology.