An ex vivo culture model for screening drug activity against in vivo phenotypes of Mycobacterium tuberculosis

• Published in: Microbiology (Society for General Microbiology) 2002-10, Vol.148 (10), p.2929-2936
• Main Authors: Turner, David J, Hoyle, Stefan L, Snewin, Valerie A, Gares, Marie-Pierre, Brown, Ivor N, Young, Douglas B
• Format: Article
• Language: English
• Subjects: Animals; Antitubercular Agents - pharmacology; BCG Vaccine - administration & dosage; BCG Vaccine - immunology; Cells, Cultured; Culture Media; Female; Humans; Luciferases - metabolism; Mice; Mice, Inbred C57BL; Microbial Sensitivity Tests - methods; Mycobacterium tuberculosis; Mycobacterium tuberculosis - classification; Mycobacterium tuberculosis - drug effects; Mycobacterium tuberculosis - growth & development; pyrazinamide; Pyrazinamide - pharmacology; Spleen - cytology; Spleen - microbiology; T-Lymphocyte Subsets - immunology; Tuberculosis, Pulmonary - immunology; Tuberculosis, Pulmonary - microbiology
• ISSN: 1350-0872; 1465-2080
• DOI: 10.1099/00221287-148-10-2929

Centre for Molecular Microbiology and Infection, Department of Infectious Diseases and Microbiology, Faculty of Medicine, Imperial College of Science, Technology and Medicine, London SW7 2AZ, UK 1 Author for correspondence: Douglas B. Young. Tel: [phone]. Fax: [phone]. e-mail: d.young{at}ic.ac.uk Since the activity of drugs against Mycobacterium tuberculosis grown in microbiological culture can differ from their activity against bacteria present in infected tissues, compounds with optimal activity against in vivo phenotypes may be overlooked in drug-discovery programmes that rely on in vitro screens. The authors have investigated the use of an ex vivo cell-culture model to assess the action of drugs on M. tuberculosis in an environment resembling that encountered during infection. Mycobacterial viability in the ex vivo model was shown to be regulated by the cell-mediated immune system, with growth inhibited by CD4 + T cells at an early stage of infection in BCG-vaccinated mice, and at a later stage after infection in naive mice. Screening of drugs in the ex vivo model demonstrated a window of pyrazinamide susceptibility that coincides with the onset of the T-cell-mediated immune response in naive or vaccinated mice. It is proposed that pyrazinamide acts on a population of bacteria that are exposed to an acidic environment as a result of immune activation. Clinically, administration of pyrazinamide during the initial phase of treatment reduces the risk of relapse after 6 months, suggesting that the early pyrazinamide-susceptible population may contribute to the later pool of mycobacteria that persist during prolonged chemotherapy. Keywords: tuberculosis, drug screening, pyrazinamide, luciferase Abbreviations: BCG, bacille Calmette–Guérin; FCS, fetal calf serum; IFN , interferon- ; r.l.u., relative light units a These authors contributed equally to the work. b Present address: The Wellcome Trust, 183 Euston Road, London NW1 2BE, UK. c Present address: Department of Biology and Biochemistry, Imperial College of Science, Technology and Medicine, London SW7 2AZ, UK.