In vitro susceptibility of 147 international clinical Mycobacterium abscessus isolates to epetraborole and comparators by broth microdilution.

Background: Mycobacterium abscessus is a highly drug-resistant non-tuberculous mycobacterium (NTM) for which treatment is limited by the lack of active oral antimycobacterials and frequent adverse reactions. Epetraborole is a novel oral, boron-containing antimicrobial that inhibits bacterial leucyl-tRNA synthetase, an essential enzyme in protein synthesis, and has been shown to have anti-M. abscessus activity in preclinical studies.

Objectives: To determine epetraborole MIC distribution for 147 recent M. abscessus isolates via broth microdilution.

Methods: M. abscessus isolates collected in 2021 from the USA (n = 122) from pulmonary sources and during 2019-22 predominantly from Europe (n = 25) from pulmonary and extrapulmonary sources had MICs determined by broth microdilution according to CLSI guidelines for epetraborole and a panel of 12 other antimycobacterials. Descriptive analyses were done on the MIC values.

Results: Of the 147 M. abscessus isolates, 101 were subspecies abscessus, 6 were bolletii and 40 were massiliense. Epetraborole MICs ranged from 0.03 to 0.25 mg/L and were consistent across subspecies. Epetraborole MIC50/MIC90 for all isolates were 0.06/0.12 mg/L. When stratified by subspecies, amikacin resistance, clarithromycin resistance and morphotype, the MIC50/MIC90 values remained 0.06/0.12 mg/L.

Conclusions: Epetraborole demonstrated potent in vitro activity against M. abscessus with MICs from 0.03 to 0.25 mg/L and consistent activity against all subspecies, resistance phenotypes and morphotypes. These data support clinical evaluation of epetraborole as a therapeutic option for M. abscessus disease.