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Abstract

Objectives

As an initial step in developing novel antibacterials against Burkholderia pseudomallei, we have characterized the FabI enoyl-ACP reductase homologues in the type II fatty acid biosynthesis pathway from this organism and performed an initial enzyme inhibition study.

Methods

A BLAST analysis identified two FabI enoyl-ACP reductase homologues, bpmFabI-1 and bpmFabI-2, in the B. pseudomallei genome, which were cloned, overexpressed in Escherichia coli and purified. Steady-state kinetics was used to determine the reaction mechanism and the sensitivity of bpmFabI-1 to four diphenyl ether FabI inhibitors. The antibacterial activity of the inhibitors was assessed using a wild-type strain of Burkholderia thailandensis (E264) and an efflux pump mutant (Bt38).

Results

Consistent with its annotation as an enoyl-ACP reductase, bpmFabI-1 catalysed the NADH-dependent reduction of 2-trans-dodecenoyl-CoA via a sequential Bi Bi mechanism. In contrast, bpmFabI-2 was inactive with all substrates tested and only bpmfabI-1 was transcriptionally active under the growth conditions employed. The sensitivity of bpmFabI-1 to four diphenyl ethers was evaluated and in each case the compounds were slow-onset inhibitors with Ki values of 0.5–2 nM. In addition, triclosan and PT01 had MIC values of 30 and 70 mg/L for B. pseudomallei as well as a wild-type strain of B. thailandensis (E264), but MIC values of <1 mg/L for the efflux pump mutant Bt38. A reduction in MIC values was also observed for the pump mutant strain with the other diphenyl ethers.

Conclusions

Provided that efflux can be circumvented, bpmFabI-1 is a suitable target for drug discovery.

B. pseudomallei, slow-onset inhibition, efflux pumps
© The Author 2011. Published by Oxford University Press on behalf of the British Society for Antimicrobial Chemotherapy. All rights reserved. For Permissions, please e-mail: [email protected]
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ORIGINAL RESEARCH
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