Evaluation of two novel antimicrobial targets in Burkholderia pseudomallei

Abstract

Burkholderia pseudomallei is a Gram-negative bacterium and the causative agent of the disease melioidosis. Melioidosis is endemic in regions of Southeast Asia and northern Australia, with human infection associated with a high mortality rate. The disease can manifest in several forms, including pneumonia, septicaemia or a chronic infection which can affect multiple organs and persist for months or years. This makes treatment of B. pseudomallei infection extremely problematic, complicated further by its inherent antibiotic resistance. For this reason new antimicrobials are required that target novel pathways within the cell.

The aim of this study was to evaluate two proteins in B. pseudomallei as future targets for antimicrobial drugs. These proteins included an essential target, inhibition of which would result in cell death, and a second that was predicted to be crucial for virulence. The Min system is responsible for the correct placement of the cell division apparatus. It is made up of three proteins; MinC, MinD and MinE, where MinE is predicted to be essential in B. pseudomallei. The virulence target chosen was PspA, the main effector of the Phage-shock protein (Psp) response. The Psp response is an extracytoplasmic response system that is vital for maintenance of the inner membrane when the cell encounters stressful conditions.

In order to validate MinE as an essential target in B. pseudomallei, a number of conditional mutagenesis techniques were used to inactivate the gene. This study found that the min operon was not essential when all three genes were inactivated, but an imbalance any of the min genes did have a detrimental effect on the survival of the bacteria, indicating that this would provide an ideal target for inhibitors. The Psp response was fully characterised by creating a knockout mutant in the pspA gene. Deletion of pspA caused a growth defect during prolonged growth in a liquid culture, also displaying reduced survival in a macrophage infection during this stage of its lifecycle. However, the ?pspA mutant did not show attenuation when tested in multiple infection models and so was not thought to play a major role in the virulence of B. pseudomallei. The results from this study indicate the PspA would not make an effective candidate for an antimicrobial target.

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ORCID for Ali Tavassoli: orcid.org/0000-0002-7420-5063

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