Novel mutations in the <i>marR</i> gene ( <i>MAB_2648c</i> ) modify nitroxoline activity in <i>Mycobacterium abscessus</i>

<i>Mycobacterium abscessus</i> is a fast-growing nontuberculous mycobacterium that can cause severe disease and poses a significant challenge for clinical management. New drugs are urgently needed for more effective treatment. Nitroxoline, an antibiotic used for treating urinary tract infections in Europe, has recently been shown to have promising activity against <i>M. abscessus</i>. However, the mechanism of its modified activity is not known. In anticipation for its potential clinical use, in this study, we investigated the mechanism of nitroxoline activity modification through mutant selection followed by whole-genome sequencing. We identified mutations in a transcriptional repressor MarR (<i>MAB_2648</i>c) controlling the expression of efflux pumps MmpS5-MmpL5 family that are associated with nitroxoline activity modification. Complementation of the mutants with the wild-type <i>marR</i> gene restored the MIC values to levels comparable to those of the wild-type strain. This study elucidates the key mechanism of how <i>M. abscessus</i> mutations modify the activity of nitroxoline, which has significant implications for rapid molecular detection of drug-resistant <i>M. abscessus</i> and for further studies on resistance mechanisms.