Activity of Drugs against Dormant Mycobacterium tuberculosis

• Published in: International journal of mycobacteriology 2016-12, Vol.5 (5), p.S94-S95
• Main Authors: Iacobino, A, Piccaro, G, Giannoni, F, Mustazzolu, A, Fattorini, L
• Format: Article
• Language: English
• Subjects: 0 Mycobacterium tuberculosis; Caseous granuloma; Cellular granuloma; Drug therapy; Drugs; Hydrophilic drugs; Infectious Disease; Lipophilic drugs; Medical Education; Metronidazole; Mycobacterium tuberculosis; Rifapentine; Tuberculosis
• ISSN: 2212-5531; 2212-554X
• DOI: 10.1016/j.ijmyco.2016.09.061

Abstract Objective/Background Heterogeneous mixtures of cellular and caseous granulomas coexist in the lungs of tuberculosis (TB) patients, with Mycobacterium tuberculosis ( Mtb ) existing from actively replicating (AR) to dormant, nonreplicating (NR) stages. Within cellular granulomas, the pH is estimated to be less than 6, whereas in the necrotic centres of hypoxic, cholesterol/triacylglycerol-rich, caseous granulomas, the pH varies between 7.2 and 7.4. To combat TB, we should kill both AR and NR stages of Mtb . Dormant Mtb remodels lipids of its cell wall, and so lipophilic drugs may be active against NR Mtb living in caseous, lipid-rich, granulomas. Lipophilicity is expressed as log P , that is, the logarithm of the partition coefficient ( P ) ratio Poctanol / Pwater . In this study, the activity of lipophilic drugs (log P > 0) and hydrophilic drugs (log P ⩽ 0) against AR and NR Mtb was measured in hypoxic conditions under acidic and slightly alkaline pHs. Methods The activity of drugs was determined against AR Mtb (5-day-old aerobic cells: A5) and NR Mtb (12- and 19-day-old hypoxic cells: H12 and H19) in a Wayne dormancy model of Mtb H37Rv at pH 5.8, to mimic the environment of cellular granulomas. Furthermore, AR and NR bacilli were grown for 40 days in Wayne models at pH 6.6, 7.0, 7.4, and 7.6, to set up conditions mimicking the caseous granulomas (hypoxia + slightly alkaline pH), to measure drug activity against NR cells. Mtb viability was determined by colony-forming unit (CFU) counts. Results At pH 5.8, lipophilic drugs (rifampin, rifapentine, bedaquiline, PA-824, clofazimine, nitazoxanide: log P ⩾ 2.14) reduced CFU of all cells (H12, H19, and A5) by ⩾2log10 . Among hydrophilic drugs (isoniazid, pyrazinamide, ethambutol, amikacin, moxifloxacin, metronidazole: log P ⩽ .01), none reduced H12 and H19 CFUs by ⩾2log10 , with the exception of metronidazole. When Mtb was grown at different pHs the following Mtb growth was noted: at pH 6.6, AR cells grew fluently while NR cells grew less, with a CFU increase up to Day 15, followed by a drop to Day 40. AR and NR Mtb grown at pH 7.0, 7.4, and 7.6 showed up to 1 log10 CFU lower than their growth at pH 6.6. The pHs of all AR cultures tended to reach pH 7.2–7.4 on Day 40. The pHs of all NR cultures remained stable at their initial values (6.6, 7.0, 7.4, and 7.6) up to Day 40. The activity of drugs against H12 and H19 cells was tested in hypoxic conditions at pH 7.3. Under these conditions, the lipophilic drug