The intracellular replication profiles for each isolate were initially determined in a cell culture model using murine macrophages. This was performed using a modified intracellular replication assay where 250 μg/ml kanamycin was used to kill extracellular bacteria, as validated below. Initially, the minimum

inhibitory concentration (MIC) of kanamycin for each strain was determined and found to be 16-128 μg/ml (Table 1). All of the strains tested were unable to grow in the presence of 250 μg/ml kanamycin in broth. Similarly, supernatants of J774A.1 cell cultures containing 250 μg/ml kanamycin and infected with any of the strains did not contain viable bacteria when samples were plated onto agar. To test for harmful effects of kanamycin on eukaryotic cell lines, cell toxicity Caspase inhibitor in vivo assays (LDH assays) were carried out

CT99021 on culture supernatants from uninfected J774A.1 cells that had been cultured in the presence of 250 μg/ml kanamycin. There was no significant difference between the LDH levels of these culture supernatants compared to control supernatants from J774A.1 cells cultured in the absence of kanamycin (data not shown). Table 1 Burkholderia isolates used in this study. Isolate Description and reference MIC (μg/ml kanamycin) Virulence in mice by i.p. route B. pseudomallei       K96243 Clinical isolate from Thailand, sequenced strain [26] 128 MLD = 262 (i.p.) [7] 576 Clinical isolate from Thailand [28] 128 MLD = 80 (i.p.) [7] 708a Gentamicin-sensitive isolate from Thailand [9] 16 MLD = 2.3 × 103 (i.p.) [7] B. thailandensis       E264 Environmental isolate, selleckchem sequenced strain [10, 37] 128 1/10 survivors at 107 cfu [16] Phuket 4W-1 Water isolate from Thailand [38] 128

2/10 survivors at 107 cfu [16] CDC3015869 Clinical isolate from Texas; abbreviated as CDC301 [39] 128 8/10 survivors at 107 cfu [16] CDC2721121 Clinical isolate from Louisiana; abbreviated as CDC272 [39] 128 10/10 survivors at 107 cfu [16] B. oklahomensis       C6786 Clinical isolate from Oklahoma [40] 128 10/10 survivors at 107 cfu [16] E0147 Clinical isolate from Georgia [41] 128 10/10 survivors at 107 cfu [16] Description of the Burkholderia strains used in this study, their susceptibility to kanamycin as described by the minimum inhibitory concentration (MIC) and a summary of published data on virulence of these isolates in mice described as the median lethal dose (MLD) in colony forming units or as number of survivors. The first parameter that was assessed in the macrophage model was internalisation efficiencies of the Burkholderia strains. Bacteria released from J774A.1 macrophages lysed 2 hrs post infection were enumerated on agar plates and compared to the input number. There was no significant difference between the degree of internalisation of B. pseudomallei, B. thailandensis or B. oklahomensis into murine macrophages (Figure 1A).