Adaptation and Antibiotic Tolerance of Anaerobic Burkholderia pseudomallei

Abstract

The Gram-negative bacterium Burkholderia pseudomallei is the etiological agent of melioidosis and is remarkably resistant to most classes of antibacterials. Even after months of treatment with antibacterials that are relatively effective in vitro, there is a high rate of treatment failure, indicating that this pathogen alters its patterns of antibacterial susceptibility in response to cues encountered in the host. The pathology of melioidosis indicates that B. pseudomallei encounters host microenvironments that limit aerobic respiration, including the lack of oxygen found in abscesses and in the presence of nitric oxide produced by macrophages. We investigated whether B. pseudomallei could survive in a nonreplicating, oxygen-deprived state and determined if this physiological state was tolerant of conventional antibacterials. B. pseudomallei survived initial anaerobiosis, especially under moderately acidic conditions similar to those found in abscesses. Microarray expression profiling indicated a major shift in the physiological state of hypoxic B. pseudomallei, including induction of a variety of typical anaerobic-environment-responsive genes and genes that appear specific to anaerobic B. pseudomallei. Interestingly, anaerobic B. pseudomallei was unaffected by antibacterials typically used in therapy. However, it was exquisitely sensitive to drugs used against anaerobic pathogens. After several weeks of anaerobic culture, a significant loss of viability was observed. However, a stable subpopulation that maintained complete viability for at least 1 year was established. Thus, during the course of human infection, if a minor subpopulation of bacteria inhabited an oxygen-restricted environment, it might be indifferent to traditional therapy but susceptible to antibiotics frequently used to treat anaerobic infections.

Gene and Protein Expression in Response to Different Growth Temperatures and Oxygen Availability in Burkholderia thailandensis

“…Our proteomics data indicate that expression of proteins involved in PHA synthesis is downregulated in oxygen-limiting conditions (Table 2). However, previous reports had suggested increased transcription levels of genes involved in PHA biosynthesis in response to lack of oxygen in other Burkholderia species [25], [26], [33]. Thus, to confirm the results of our proteomic analysis, we assessed formation of PHA granules in BtCDC272 grown in different conditions by TEM observations.…”

“…Since genes encoding ribosomal proteins are known to be more expressed in optimal growth conditions, induction in anoxic conditions was unexpected; in addition, this result might seem at odds with previous findings showing decreased expression of protein synthesis-related genes in response to hypoxia in different Burkholderia species [25], [26]. In these reports, however, experiments had been carried on using exponentially-growing bacteria.…”

Nitrate Sensing and Metabolism Inhibit Biofilm Formation in the Opportunistic Pathogen Burkholderia pseudomallei by Reducing the Intracellular Concentration of c-di-GMP

“…Members of the Burkholderia genus, including the clinical isolate B. pseudomallei K96243, can grow in anaerobic conditions using nitrate as an alternative terminal electron acceptor, much like other facultative anaerobic bacteria (Yabuuchi et al, 1992; Hamad et al, 2011). The effects of anaerobic growth using nitrate on the physiology of B. pseudomallei biofilms remains largely undetermined.…”

Nitric oxide-dependent killing of aerobic, anaerobic and persistent Burkholderia pseudomallei

“…The B. pseudomallei bacterial pellets were resuspended in EGYE culture medium that had been deoxygenated in the anaerobic chamber for 24 h. The bacteria were adapted to the anaerobic environment for 2 h prior to challenge with the NO donors. Long-term anaerobiosis was achieved using shaking tubes in the “Wayne” model first described for work with Mycobacterium tuberculosis , and recently adapted for work with B. pseudomallei (16, 17). Hungate anaerobic glass tubes containing magnetic stir bars and filled with 14 ml of LBG broth were inoculated with log phase B. pseudomallei and sealed with Hungate stoppers and airtight screw caps.…”