Activity of Drug Combinations against Mycobacterium abscessus Grown in Aerobic and Hypoxic Conditions

Abstract

Infections caused by Mycobacterium abscessus (Mab), an environmental non-tuberculous mycobacterium, are difficult to eradicate from patients with pulmonary diseases such as cystic fibrosis and bronchiectasis even after years of antibiotic treatments. In these people, the low oxygen pressure in mucus and biofilm may restrict Mab growth from actively replicating aerobic (A) to non-replicating hypoxic (H) stages, which are known to be extremely drug-tolerant. After the exposure of Mab A and H cells to drugs, killing was monitored by measuring colony-forming units (CFU) and regrowth in liquid medium (MGIT 960) of 1-day-old A cells (A1) and 5-day-old H cells (H5). Mab killing was defined as a lack of regrowth of drug-exposed cells in MGIT tubes after >50 days of incubation. Out of 18 drugs tested, 14-day treatments with bedaquiline-amikacin (BDQ-AMK)-containing three-drug combinations were very active against A1 + H5 cells. However, drug-tolerant cells (persisters) were not killed, as shown by CFU curves with typical bimodal trends. Instead, 56-day treatments with the nitrocompounds containing combinations BDQ-AMK-rifabutin-clarithromycin-nimorazole and BDQ-AMK-rifabutin-clarithromycin-metronidazole-colistin killed all A1 + H5 Mab cells in 42 and 56 days, respectively, as shown by lack of regrowth in agar and MGIT medium. Overall, these data indicated that Mab persisters may be killed by appropriate drug combinations.

Distinct Effects of Moxifloxacin and Bedaquiline on Growing and ‘Non-Culturable’ Mycobacterium abscessus

“…MIC assays are not enough to evaluate the bactericidal activity of tested agents against M. abscessus, and viability counting after challenge to antibacterial agents is essential to avoid an overestimation of their effects, as already recommended [16,17,27] and shown in this study. Particularly, both CFU and MPN tests are essential to monitor antibacterial effects of a tested agent in light of further development of non-culturability, as observed in our experiments for some antibiotics at least.…”

“…Dormant cells of M. abscessus have found limited application in tests for the bactericidal activity of potent drugs or their combinations. Particularly, M. abscessus cells, which underwent starvation in PBS [16], or survived under oxygen deprivation and nutrient starvation in a non-replicative state [17], or subjected to hypoxic conditions [27], have been the main targets for assessing bactericidal activity. Entry into the dormant state with the loss of the ability to form colonies (transiently 'non-culturable' state) is commonly and reproducibly attainable due to a deficiency of potassium ions in the culture medium, as previously demonstrated for other mycobacteria, notably, M. tuberculosis [28][29][30].…”

Challenges & Solutions for Recent Advancements in Multi-Drugs Resistance Tuberculosis: A Review

“…Then, it will reduce the time of treatment of tuberculosis and help in reducing MDR-TB. According to Lanni et al 11 and Iacobino et al, 40 the combination of Rifapentine and Rifampin at a neutral pH of 7.3 has shown significant results in the killing of the Mtb persisters. Not only one, but even, the combination of other drugs such as Nitazoxanide and Rifampin are equally effective against the dormant Mtb.…”

“…Temporal and spatial differences in the distribution and accumulation kinetics of medicine in lesion-specific comportment may create a window for the development of drug resistance. 11 …”

“…Temporal and spatial differences in the distribution and accumulation kinetics of medicine in lesion-specific comportment may create a window for the development of drug resistance. 11 When caseous granulomas enlarge, the necrotic centers join also with bronchial airway structures to create pulmonary cavities, that either contains both intracellular and extracellular bacilli deduced from the solubilization of phagosomes of the cavities as well as from liquefied caseum. These bacilli multiply quickly when exposed to ambient oxygen in the cavity's lumen.…”