Effects of sodium chloride on heat resistance, oxidative susceptibility, motility, biofilm and plaque formation of Burkholderia pseudomallei

Burkholderia pseudomallei is an environmental saprophyte and the causative agent of melioidosis, a severe infectious disease prevalent in tropical areas, including southeast Asia and northern Australia. In Thailand, the highest incidence of melioidosis is in the northeast region, where saline soil and water are abundant. We hypothesized that B. pseudomallei develops an ability to thrive in saline conditions and gains a selective ecological advantage over other soil-dwelling microorganisms. However, little is known about how an elevated NaCl concentration affects survival and adaptive changes in this pathogen. In this study, we examined the adaptive changes in six isolates of B. pseudomallei after growth in Luria-Bertani medium containing different concentrations of NaCl at 37°C for 6 hr. The bacteria were then investigated for resistance to heat at 50°C and killing by hydrogen peroxide (H₂O₂). In addition, flagellar production, biofilm formation, and the plaque formation efficiency of B. pseudomallei after culture in saline conditions were observed. In response to exposure to 150 and 300 mmol L⁻¹ NaCl, all B. pseudomallei isolates showed significantly increased thermal tolerance, oxidative resistance, and plaque-forming efficiency. However, NaCl exposure notably decreased the number of B. pseudomallei flagella. Taken together, these results provide insight into the adaptations of B. pseudomallei that might be crucial for survival and persistence in the host and/or endemic environments with high salinity.