A Novel Advanced Laboratory Diagnosis to Guide Tuberculosis Drug Therapy.
Recent Pat Antiinfect Drug Discov. 2015 Aug 3;
Authors: Amaral L, van Soolingen D
Tuberculosis presenting severe resistance, defined as extensively drug resistant tuberculosis (XDR TB) continues to increase world-wide to the point that resistance to all available drugs, defined as totally drug resistant tuberculosis (TDR TB) is now significantly present in India, Iran, and other countries (ex. China) and regions (ex. Central Asia) where multi-drug resistance is commonplace. Although the need for new- and more effective drugs is urgent, control of tuberculosis lies primarily in early case finding, prevention of transmission and successful therapy with available drugs. Essential to effective diagnosis and treatment is the appropriate use of a number of laboratory procedures for identification of the infecting bacteria and the selection of effective drugs. Because the outcome of each tuberculosis infection and similar infections by non-tuberculous mycobacteria (NTM) is determined by the nature of the infecting organism, but also depends on the immune response of the patient affected, it is essential that all aspects that contribute to the interaction between bacteria and patient are studied for each specific patient/infecting agent combination. This herein Current Opinion presents a proposed procedure which includes the genetic identification of the isolated Mycobacterium tuberculosis strain, the degree of antibiotic resistance exhibited by the clinical isolate to a wide panel of antibiotics used for therapy of multi-drug (MDR), XDR and TDR, the identification and evaluation of over-expressed efflux pumps of the clinical isolate which are responsible for the degree of individual resistance to specific antibiotics of the panel, the killing activity of the patient's non-killing whole blood derived macrophages with and without the presence of inhibitors of efflux pumps, and the evaluation of effective empirically demonstrated efflux pump inhibitors in combination with given antibiotics that together render the clinical isolate susceptible to antibiotics to which it was initially resistant. These methods and procedures together define the proposed approach as "Personalised Laboratory Medicine for Drug Resistant Tuberculosis". The approach presented may be subject to consideration for patenting. For the identification of the causative bacteria, several molecular tests are available (Hain, Nehren, Germany). In principle, these tests can recognize mycobacteria of the Mycobacterium tuberculosis complex and of non-tubercular mycobacterial (NTM) species. Whereas patients infected with bacteria of the former group always require treatment, patients infected by NTM in some cases, need to be treated . Because problems of resistance and transmissibility are not equally divided among the genotype families of the M. tuberculosis, molecular typing up to genotype level may yield interesting information [2, 3]. For instance some Beijing genotype family bacteria have caused large outbreaks of MDR-TB in Eastern Europe and Asia and recognizing the strains that are notorious spreaders may be of importance for treatment and for infection control of tuberculosis . In addition, early recognition of resistance to rifampicin (Rif) is of the utmost importance to trace cases of MDR/XDR-TB. For this purpose, a rapid one day procedure that identifies resistance to Rif is afforded by the identification of mutations within the beta subunit of the rpoB gene . Because resistance to Rif is almost always accompanied by resistance to isoniazid (INH) , resistance to Rif acts as a surrogate marker for identification of MDR-TB and XDR-TB . Therefore, rapid identification of patients in the need of intensified therapy is possible while pan-susceptible infections can readily be managed with four first line drugs recommended by the WHO. Confirmation of the MDR-TB phenotype of the M. tuberculosis isolate is then performed conventionally by an in vitro growth inhibition assay. Molecular tests are also available to detect mutations in the genome of M. tuberculosis associated with XDR-TB, such as the MDRTBsl kit (Hain, Nehren, Germany). There are, however, new insights that the MDR phenotype of the isolate may also be related to over-expressed efflux pumps and a simple assay that evaluates this status may be considered . If efflux pumps are up regulated, they may be inhibited by the phenothiazine thioridazine which has been used successfully with combinations of three antibiotics to which initial resistance of the clinical isolated was present, as shown by the cures of 17 XDR-TB patients of Buenos Aires, Argentina . Because pulmonary tuberculosis is primarily an infection of pulmonary macrophages that are often not able to kill the internalized bacteria, the selected therapy may be evaluated by testing the activity of the patient's own ex-vivo macrophages derived from his/her whole blood for predicting therapeutic success .
PMID: 26235217 [PubMed - as supplied by publisher]