Non-tuberculous mycobacteria (NTM) cause chronic lung infections in patients with cystic fibrosis. Among them, Mycobacterium abscessus (Mab) is the most frequently isolated species. NTMs can form an extracellular matrix, called biofilm, in the alveolar walls and airways of patients, in which oxygen decreases, causing a transition to a dormant hypoxic (anaerobic), non-replicative and drug-tolerant phase. To combat NTMs, it is therefore necessary to find new combinations of drugs active against aerobic and anaerobic forms.

In this study we tested Mab under aerobic and hypoxic conditions to study the efficacy of combinations of 8 drugs with anti-Mab activity and 10 nitro-compounds, known to be active against anaerobic bacteria. The bedaquiline+amikacin combination was highly active against aerobic bacteria, but to a lesser extent against anaerobes. The addition of a third drug increased mortality against aerobes, using moxifloxacin or clofazimine, or against anaerobes, with clarithromycin, colistin and some nitro compounds such as metronidazole and nimorazole. Therefore, to obtain a combination capable of killing both aerobic and anaerobic cells, it was necessary to use 5 drugs at the same time.

Furthermore, one of the relevant problems in antibiotic treatments is the presence of subpopulations of intrinsically multidrug-resistant bacteria, the so-called persisters. These forms are responsible for the failure of treatments and also for the emergence of genotypic resistance. The study of these forms, which has just begun, suggests that they are dormant bacteria, even in the absence of the main stimulus, i.e. hypoxia.

In conclusion, we investigated the activity of several drug combinations with promising anti-Mab activity and started to characterize the multidrug-resistant (dormant and persistent) forms that are the main enemy during drug treatments.

The research continues in the project FFC#6/2022 to identify at least one combination capable of killing both aerobic and hypoxic Mab cells in less than 1 month, which will then be explored in animal models and possible clinical studies, to shorten anti-Mab therapies in CF.