15. A 10-fold dilution of the inoculums was performed. Ten microlitres of all dilutions of bacteria in PBS were spotted onto the LB agar with and without adding sub-lethal

concentrations of menadione (400 μM), H2O2 (250 μM) and tBOOH (200 μM) [52]. Colony counts were performed after incubation at 37°C for 24 hrs. The number of colonies on plates containing oxidants was compared with that on control plates (LB agar without oxidant) and presented as % bacterial survival. % Survival = CFU (with oxidant) × 100/ CFU (without oxidant). Statistical analysis All assays were conducted in triplicate, and unpaired t-test of independent experiments was performed by statistical analysis using GraphPad Prism 6 program (STATCON). Results were considered significant at p-value ≤ 0.05. Acknowledgements This work was supported by a Research Grant from the Faculty of Tropical Medicine, Mahidol University, Fiscal year 2011. NC is supported by a Wellcome Trust Career Development Award in Public Health and Tropical

Medicine, UK (Grant: 087769/Z/08/Z). We thank Herbert P. Schweizer for providing pEXKm5 vector. We thank Prof. Srisin Khusmith for her insightful advice, and Mr. Glad Rotaru & Mr. Paul Adams, of the Office of Research Services, Faculty of Tropical Medicine, Mahidol University, for proof-reading the manuscript. Electronic supplementary material Additional file 1: Construction and verification of eFT-508 in vivo B. pseudomallei SDO mutant. A) A 566 bp DNA fragment containing 298 bp-upstream and 288 bp-downstream of the SDO gene was replaced into the B. pseudomallei K96243 genome using the pEXKm5-based allele replacement system [19]. B) PCR of B. pseudomallei wild type, SDO mutant and SDO complement strain were performed with the BPSS2242-F1 and BPSS2242-R2 primer pair (lane 1: 100–3000 bp marker ladder; lane 2: negative control; lane 3: K96243; lane 4: SDO mutant; and lane 5: SDO complement strain). Adenylyl cyclase C) PCR analysis of pEXKm5 plasmid backbone within the B. pseudomallei genome using

oriT specific primers (lane 1: 100–3000 bp marker ladder; lane 2: negative control; lane 3: SDO mutant before sucrose selection; lane 4: SDO complement strain before sucrose selection; lane 5: SDO mutant after sucrose selection; and lane 6: SDO complement strain after sucrose selection). (TIFF 742 KB) References 1. White NJ: Melioidosis. Lancet 2003, 361:1715–1722.PubMedCrossRef 2. Currie BJ, Jacups SP: Intensity of rainfall and severity of melioidosis, Australia. Emerg Infect Dis 2003, 9:1538–1542.PubMedCrossRef 3. Leelarasamee A, Trakulsomboon S, Kusum M, Dejsirilert S: Isolation rates of Burkholderia pseudomallei among the four regions in Thailand. Southeast Asian J Trop Med Public Health 1997, 28:107–113.PubMed 4. Vuddhakul V, Tharavichitkul P, Na-Ngam N, Jitsurong S, Kunthawa B, Noimay P, Noimay P, Binla A, Thamlikitkul V: Epidemiology of Burkholderia pseudomallei in Thailand. Am J Trop Med Hyg 1999, 60:458–461.PubMed 5.