Evaluation of the post-antibiotic effect against Mycobacterium abscessus by a bioluminescence method

Mycobacterium abscessus is an emerging pathogen, extremely difficult to treat and with no FDA-approved drugs in clinic. Many antibiotics have limited activity against M. abscessus, and their clinical breakpoints are not available. Post-antibiotic effect (PAE) is a determinant of antibiotic efficacy and could inform drug dosing regimens. Here, we evaluated and compared the duration of the PAE for seven antibiotics (amikacin, bedaquiline, cefoxitin, clarithromycin, imipenem, linezolid, and tigecycline), alone and in combination, toward M. abscessus. The bioluminescence method used to evaluate the PAE was confirmed through conventional viable counting and offered a faster and easier approach to access PAE of individual antibiotics, their combinations, and could facilitate translation into clinical dosing. Clarithromycin and tigecycline induced a strong PAE (8.3-25.7 and 10.6-22 h, respectively), while amikacin (2-11 h), bedaquiline (1.8-4.5 h), imipenem (5 h), and linezolid (0.8-2 h) displayed moderate PAE activities. Cefoxitin showed no PAE. Inclusion of clarithromycin into four three-drug combinations used in the initial parenteral phase resulted in significant extension of the PAE in concordance with the better outcomes of these drug regimens. These results provide reference PAE values for M. abscessus-active antibiotics and their combinations and offer a method to facilitate PAE testing in vitro.IMPORTANCEClinical infections with Mycobacterium abscessus are on the rise globally, with no reliable cure options. Current treatment options rely on multidrug therapy including macrolide-based combinations and/or amikacin; however, minimum inhibitory concentration (MIC) cutoffs for susceptibility and resistance have established clinical relevance only for macrolides and amikacin. No other M. abscessus-active antibiotics have validated MIC cutoff points or available other parameters such as post-antibiotic effect (PAE) that could predict clinical response and dosing efficacy. Here, we report on the generation of a recombinant M. abscessus reference strain expressing the bacterial lux genes and its usage to monitor regrowth and quantify PAEs for current M. abscessus antibiotics and their combinations used in clinic. These data provide reference numbers for current M. abscessus antibiotics and offer a simplified approach to facilitate testing of new antibiotics and their combinations.