Characterization of the MacA–MacB efflux system in Neisseria gonorrhoeae

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Abstract
Objectives: A homologue of the MacA–MacB ABC transporter of Escherichia coli, which recognizes and exports macrolides, was identified in Neisseria gonorrhoeae. This study was undertaken to determine whether gonococci could use the MacA–MacB homologue to express decreased susceptibility to macrolides. Methods: Techniques of DNA sequencing, gene cloning and expression of recombinant proteins in E. coli, gene mutation construction, transcriptional analysis and antimicrobial susceptibility testing were used in the study. Results: Although the gonococcal MacA–MacB efflux pump enhanced bacterial resistance to macrolides when overexpressed in an E. coli background, its loss in a gonococcal clinical isolate only slightly decreased bacterial resistance to azithromycin and erythromycin. However, a mutation in the −10 sequence of the promoter used in macAB expression enhanced the macrolide resistance of gonococci that produced a defective MtrC–MtrD–MtrE pump, which also recognizes macrolides. Conclusions: The results from this study indicate that gonococci can employ both the MacA–MacB and MtrC–MtrD–MtrE efflux pumps to develop resistance to macrolides, particularly if mutations develop in the promoter that drives transcription of macAB.