Author Proof part of 10.2217/17460913.3.2.xxx © 2008 Future Medicine Ltd ISSN 1746-0913 PERSPECTIVE Future Microbiol. (2008) 3(2), xxx–xxx 1 The TB laboratory of the future: macrophage- based selection of XDR-TB therapeutics Marta Martins, Miguel Viveiros & Leonard Amaral † † Author for correspondence Unit of Mycobacteriology, Instituto de Higiene e Medicina Tropical, Universidade Nova de Lisboa, Rua da Junqueira, 96, 1349–008 Lisboa, Portugal Tel.: +35 121 365 2600; Fax: +35 121 363 2105; lamaral@ihmt.unl.pt Keywords: derivatives, K + inhibition, macrophages, MDR-TB, Mycobacterium tuberculosis, phenothiazines, thioridazine, XDR-TB Therapy of multidrug-resistant (MDR)-TB is highly problematic; that of extensively drug-resistant (XDR)-TB even more so. Both infections result in high mortality, especially if the patient is coinfected with HIV or presents with AIDS. Selection of therapy for these infections is limited and, for most situations, it is performed ‘blind’. However, there is a solution for the selection of effective therapy and this is presented herein. Ideal therapy of the patient infected with MDR-TB or XDR-TB can be determined a priori by the mycobacteriology laboratory. This would involve the isolation of the patient’s macrophages, the phagocytosis of the mycobacterial isolate and the presentation of the antitubercular agent to the macrophage–bacterium complex. This system is reviewed in its entirety and its potential and feasibility are supported by hard experimental demonstrations. Multi- & extensively drug-resistant TB Multidrug-resistant (MDR) Mycobacterium tuberculosis (MDR-TB) is resistant to the two most effective antitubercular drugs, isoniazid (INH) and rifampicin (RIF), and even under the best of circumstances, that is, under appropriate therapy, patient compliance and under direct observable therapy (DOT), it produces signifi- cant mortality [1]. When the infection takes place in a patient that is coinfected with HIV and has advanced to AIDS, mortality is almost always certain within a year, regardless of therapy [1–3]. To make matters worse, MDR-TB has pro- gressed to extensively drug-resistant (XDR) M. tuberculosis, defined by resistance to INH, RIF, any fluoroquinolone and at least one of the three injectable second-line drugs (capreomycin, kanamycin and amikacin) [2–4]. Even though individual resistance of wild-type M. tuberculosis to these drugs exceeds the frequency of individ- ual resistance to INH and RIF [2,4], these drugs in combination have been recommended for the therapy of XDR-TB [5]. Pulmonary TB is an intracellular infection of the alveolar macrophage. Because this cell has lit- tle killing activity of its own, the M. tuberculosis exists in situ for decades without causing any overt symptoms of infection. In fact, in the absence of immuno-incompetence, less than 10% of all infections progress to active disease [1,5] – the phase characterized by the release of the organism from its macrophage prison which is now extracel- lular and eventually manifested in patient sputum. Owing to the intracellular nature of the infection, in order for a given drug to be thera- peutically effective it must be able to penetrate the macrophage and have activity against the in situ localized organism. Consequently, although liter- ally thousands of compounds have been shown to have in vitro activity against M. tuberculosis [6], only a very few have activity against the organism at its intracellular location [7,8]. This simple fact means that if an agent is to be therapeutically active against antibiotic susceptible M. tuberculosis, MDR-TB and even XDR-TB, it must first be shown to be active where these strains of M. tuberculosis are to be found, namely, the human macrophage [8,9]. It is the purpose of this mini review to present cogent support for the use of the human macro- phage model in the clinical TB laboratory as the only realistic means by which effective anti- MDR/XDR-TB compounds can be a priori selected for the therapy of the MDR/XDR-TB- infected patient. Moreover, because time is of the essence for the identification and antibiotic sus- ceptibility of MDR/XDR-TB, rapid responses are required if this infection is to be curtailed, and so we discuss the system that has been in place at our laboratory for close to 5 years, which identifies MDR-TB within 1 day of receiving the specimen. Identification of an MDR-TB infection within 1 day of receiving the clinical specimen: The Faster TB Track Program As a consequence of the resurgence of TB and MDR-TB in the city of New York (USA) during the early 1990s, the New York State Department of Health instituted the TB Fast Track Program [10–12]. This program required that the clinical specimen be accompanied by a positive acid-fast stained sputum after which its reception resulted in the shunting of the specimen in the most rapid manner (fast track) for the identification of the