Dissecting erm (41)-Mediated Macrolide-Inducible Resistance in Mycobacterium abscessus

Abstract

Macrolides are the cornerstone of Mycobacterium abscessus multidrug therapy, despite that most patients respond poorly to this class of antibiotics due to the inducible resistance phenotype that occurs during drug treatment. This mechanism is driven by the macrolide-inducible ribosomal methylase encoded by erm(41), whose expression is activated by the transcriptional regulator WhiB7. However, it has been debated whether clarithromycin and azithromycin differ in the extent to which they induce erm(41)-mediated macrolide resistance. Herein, we show that macrolide resistance is induced more rapidly in various M. abscessus isolates upon exposure to azithromycin than to clarithromycin, based on MIC determination. Macrolide-induced expression of erm(41) was assessed in vivo using a strain carrying tdTomato placed under the control of the erm(41) promoter. Visualization of fluorescent bacilli in infected zebrafish demonstrates that azithromycin and clarithromycin activate erm(41) expression in vivo. That azithromycin induces a more rapid expression of erm(41) was confirmed by measuring the β-galactosidase activity of a reporter strain in which lacZ was placed under the control of the erm(41) promoter. Shortening the promoter region in the lacZ reporter plasmid identified DNA elements involved in the regulation of erm(41) expression, particularly an AT-rich motif sharing partial conservation with the WhiB7-binding site. Mutation of this motif abrogated the macrolide-induced and WhiB7-dependent expression of erm(41). This study provides new mechanistic information on the adaptive response to macrolide treatment in M. abscessus.

Non-tuberculous mycobacteria and the rise of Mycobacterium abscessus

“…A T-C polymorphism in erm41 at position 28 is responsible for inducible macrolide resistance in M. abscessus and M. bolletii (only isolates with T28 develop resistance), whereas M. massiliense contains deletions in erm41 and thus a non-functional enzyme, rendering this subspecies susceptible to macrolides 147,148 . Macrolide-induced expression of erm41 was recently assessed in vivo with a fluorescent reporter strain carrying tdTomato placed under the control of the erm41 promoter 149 . Visualization of fluorescent bacilli in infected zebrafish exposed to azithromycin or clarithromycin demonstrated induction of erm41 expression.…”

“…The multidrug-inducible transcriptional activator WhiB7 (MAB_3508c) modulates the expression of a large set of genes, such as erm41 and eis2, and contributes to resistance to macrolides and aminoglycosides 150 . Indeed, deletion of whiB7 increased susceptibility to clarithromycin and amikacin 150 and mutations in the WhiB7binding motif in the erm41 promoter region abrogated macrolide-induced resistance 149 . Importantly, exposure of M. abscessus to subinhibitory concentrations of clarithromycin induced expression of whiB7 and conferred resistance to amikacin and clarithromycin due to the upregulation of erm41 and eis2 (reF.…”

Rifabutin Suppresses Inducible Clarithromycin Resistance in Mycobacterium abscessus by Blocking Induction of whiB7 and erm41

“…Intrinsic CLR resistance is inducible. Exposure to subinhibitory concentrations of CLR induces transcription of whiB7 encoding a transcriptional activator, which in turn induces transcription of erm41 [6][7][8][9].…”

<p>Antimicrobial Susceptibility of <em>Mycobacterium abscessus</em> Complex Clinical Isolates from a Chinese Tertiary Hospital</p>

“…The primary innate mechanism underlying CLA resistance in MABC involves an increase in expression of the erythromycin ribosomal methylase gene, erm (41). Induction of erm(41) is mediated by the transcription factor whiB7, 9 and rifabutin suppresses inducible CLA resistance by preventing induction of whiB7 and erm(41) expression. 10 Inducible resistance to CLA was identified in a sequevar with an intact erm(41) but with a single-nucleotide polymorphism (C to T) at position 28 11 (C at position 28 in M. abscessus results in CLA susceptibility).…”