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

Abstract

Clarithromycin (CLR) is the corner stone in regimens for the treatment of lung disease caused by Mycobacterium abscessus (Mab). However, many strains harbor the CLR-inducible CLR resistance gene erm41, encoding a ribosome methylase. Induction of erm41 is mediated by the transcription factor whiB7. We hypothesized that an inhibitor of RNA synthesis should be able to block the whiB7–erm41 induction response to CLR exposure and thus suppress CLR resistance. Recently, we discovered that the rifampicin analog rifabutin (RFB) shows attractive potency against Mab. To determine whether RFB-CLR combinations are synergistic, a checkerboard analysis against a collection of erm41 positive and negative Mab strains was carried out. This revealed synergy of the two drugs for erm41 positive but not for erm41 negative strains. To determine whether RFB’s potentiation effect was due to inhibition of the transcriptional induction of the whiB7–erm41 resistance system, we measured the effect of CLR alone and in combination with RFB on whiB7 and erm41 mRNA levels. CLR alone strongly induced whiB7 and erm41 expression as expected. The synergistic, growth-inhibiting combination of RFB with CLR blocked induction of both genes. These results suggest that RFB suppresses inducible CLR resistance by preventing induction of whiB7 and erm41 expression.

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

“…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). Notably, M. massiliense strains with a CLA susceptible phenotype have a nonfunctional erm (41) gene.…”

Differentialin vitroactivity of individual drugs and bedaquiline-rifabutin combinations against actively multiplying and nutrient-starvedMycobacterium abscessus

“…As a rifamycin, rifabutin inhibits DNA-dependent RNA polymerase and initiation of transcription. Several groups have reported in vitro synergistic activity between rifabutin and clarithromycin against M. abscessus (35, 36, 55), and Aziz et al have specifically linked this synergism to rifabutin-induced transcriptional inhibition of genes associated with inducible macrolide resistance in M. abscessus, thus rendering the bacteria fully susceptible to clarithromycin (55). In vitro exposure of actively-growing M. tuberculosis to bedaquiline has been shown to induce specific transcriptional responses which may help the bacteria counteract ATP depletion, thus causing the limited or delayed activity of bedaquiline (56, 57).…”

Alternative and Experimental Therapies of Mycobacterium abscessus Infections

“…This antimicrobial activity was approximately 10-fold greater than the activity of rifampin and rifapentine, and it was evident in clarithromycin-resistant strains [27]. Rifabutin was found to be synergistic to clarithromycin against isolates with an intact erm(41) gene, and it has been shown to suppress inducible clarithromycin resistance [29], suggesting this drug combination may be of great clinical benefit.…”

“…Activity against clinical and reference strains, including CLR resistant strains [27,28] Synergy with CLR, suppresses CLR induced resistance [29].…”