Abstract
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.
Highlights
Burkholderia pseudomallei is a Gram-negative pathogenic bacterium responsible for melioidosis in humans and animals
The relevance of this has been shown in Salmonella enterica serovar Typhimurium (12), Staphylococcus aureus (Park et al, 2012), and Listeria monocytogenes (Garner, James, Callahan, Wiedmann, & Boor, 2006), whereby bacteria cultured in medium-containing high NaCl show increased heat tolerance (Park et al, 2012; Yoon, Park, Oh, Choi, & Yoon, 2013), antibiotic resistance (Yoon et al, 2013), and invasion ability into host cells (Garner et al, 2006; Yoon et al, 2013)
The percentage of surviving bacteria among the B. pseudomallei isolates grown in salt-free medium in the presence of H2O2 was significantly lower than the bacteria exposed to salt at a concentration of 150 mmol L−1 NaCl (p = .046 for K96243, p = .039 for 153, p = .019 for 576, p = .027 for 1026b, p = .043 for 1530, and p = .014 for 1634), or those exposed to 300 mmol L−1 NaCl (p = .004 for K96243, p = .004 for 153, p < .001 for 576, p = .010 for 1026b, p = .011 for 1530, and p < .001 for 1634)
Summary
Burkholderia pseudomallei is a Gram-negative pathogenic bacterium responsible for melioidosis in humans and animals. There is evidence of a link between high NaCl concentrations and an ability to survive in saline conditions in other closely related organisms, namely, the Burkholderia cepacia complex (BCC). Several studies have shown that exposure to NaCl can influence the adaptive survival and virulence of pathogenic bacteria The relevance of this has been shown in Salmonella enterica serovar Typhimurium (12), Staphylococcus aureus (Park et al, 2012), and Listeria monocytogenes (Garner, James, Callahan, Wiedmann, & Boor, 2006), whereby bacteria cultured in medium-containing high NaCl show increased heat tolerance (Park et al, 2012; Yoon, Park, Oh, Choi, & Yoon, 2013), antibiotic resistance (Yoon et al, 2013), and invasion ability into host cells (Garner et al, 2006; Yoon et al, 2013). The bacteria under salt stress were tested for heat resistance, oxidative susceptibility, swarm motility, flagellar production, and biofilm and plaque formation
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