The paper gives the results of a demonstration project to introduce a test for drug sensitivity to second-line antituberculous agents for patients with multidrug-resistant (MDR) tuberculosis at a routine large Russian laboratory. Two hundred and thirty MDR isolates were examined; of them 8.7% had extreme drug resistance. The cost of this test was estimated to be US $ 33.4. The introduction of this test is possible and essential for the precise and timely choice of antituberculous therapy for patients with MDR tuberculosis.

BACKGROUND: Data on global trends in resistance to antituberculosis drugs are lacking. METHODS: We expanded the survey conducted by the World Health Organization and the International Union against Tuberculosis and Lung Disease to assess trends in resistance to antituberculosis drugs in countries on six continents. We obtained data using standard protocols from ongoing surveillance or from surveys of representative samples of all patients with tuberculosis. The standard sampling techniques distinguished between new and previously treated patients, and laboratory performance was checked by means of an international program of quality assurance. RESULTS: Between 1996 and 1999, patients in 58 geographic sites were surveyed; 28 sites provided data for at least two years. For patients with newly diagnosed tuberculosis, the frequency of resistance to at least one antituberculosis drug ranged from 1.7 percent in Uruguay to 36.9 percent in Estonia (median, 10.7 percent). The prevalence increased in Estonia, from 28.2 percent in 1994 to 36.9 percent in 1998 (P=0.01), and in Denmark, from 9.9 percent in 1995 to 13.1 percent in 1998 (P=0.04). The median prevalence of multidrug resistance among new cases of tuberculosis was only 1.0 percent, but the prevalence was much higherin Estonia (14.1 percent), Henan Province in China (10.8 percent), Latvia (9.0 percent), the Russian oblasts of Ivanovo (9.0 percent) and Tomsk (6.5 percent), Iran (5.0 percent), and Zhejiang Province in China (4.5 percent). There were significant decreases in multidrug resistance in France and the United States. In Estonia, the prevalence in all cases increased from 11.7 percent in 1994 to 18.1 percent in 1998 (P<0.001). CONCLUSIONS: Multidrug-resistant tuberculosis continues to be a serious problem, particularly among some countries of eastern Europe. Our survey also identified areas with a high prevalence of multidrug-resistant tuberculosis in such countries as China and Iran.

The incidence of tuberculosis has been increasing substantially on a worldwide basis over the past decade, but no tuberculosis-specific drugs have been discovered in 40 years. We identified a diarylquinoline, R207910, that potently inhibits both drug-sensitive and drug-resistant Mycobacterium tuberculosis in vitro (minimum inhibitory concentration 0.06 mug/ml). In mice, R207910 exceeded the bactericidal activities of isoniazid and rifampin by at least 1 log unit. Substitution of drugs included in the World Health Organization's first-line tuberculosis treatment regimen (rifampin, isoniazid, and pyrazinamide) with R207910 accelerated bactericidal activity, leading to complete culture conversion after 2 months of treatment in some combinations. A single dose of R207910 inhibited mycobacterial growth for 1 week. Plasma levels associated with efficacy in mice were well tolerated in healthy human volunteers. Mutants selected in vitro suggest that the drug targets the proton pump of adenosine triphosphate (ATP) synthase.

The response to short-course chemotherapy of patients with pulmonary tuberculosis caused by drug-resistant Mycobacterium tuberculosis was examined in 12 controlled trials carried out during the past decade in Africa, Hong Kong, and Singapore. Among those with initial resistance to isoniazid and/or streptomycin, failures during chemotherapy were encountered in 17% of 23 patients given a 6-month regimen of isoniazid and rifampin and in 12% of 264 patients given rifampin only in an initial 2-month intensive phase of their regimen. The proportion of failures fell as the number of drugs in the regimen and the duration of treatment with rifampin were increased, to reach 2% of 246 patients receiving 4 or 5 drugs including rifampin in 6-month regimens. The sterilizing activity of the regimens, whether these included rifampin or pyrazinamide, was little influenced by initial resistance, because the sputum conversion rate at 2 months was similar to that in patients with initially sensitive bacilli, and the relapse rates after chemotherapy were only a little higher. The response in the 11 patients with initial rifampin resistance was, however, much less good, failure during chemotherapy occurring in 5 and relapse afterwards in a further 3 patients. This review demonstrates the value of rifampin in preventing failure caused by the emergence of resistance during treatment and the greater sterilizing activity of rifampin and pyrazinamide compared with that of isoniazid and streptomycin.

The emergence of strains of Mycobacterium tuberculosis that are resistant to antimycobacterial agents is a worldwide problem whose global magnitude is not well described. We reviewed and tabulated 63 surveys of resistance to antituberculous drugs that were performed between 1985 and 1994. Rates of primary resistance to isoniazid, administered as a single agent, ranged from 0 to 16.9%(median rate, 4.1%); to streptomycin, 0.1%-23.5%(median, 3.5%); to rifampin, 0-3.0%(median, 0.2%); and to ethambutol, 0-4.2%(median, 0.1%). The rates of acquired resistance to these agents, which were higher than those of primary resistance, were as follows: isoniazid, 4.0%-53.7%(median rate, 10.6%); streptomycin, 0-19.4%(median, 4.9%); rifampin 0-14.5%(median, 2.4%); and ethambutol, 0-13.7%(median, 1.8%). The highest rates of multidrug-resistant tuberculosis have been reported in Nepal (48.0%), Gujarat, India (33.8%), New York City,(30.1%), Bolivia (15.3%), and Korea (14.5%). The WHO (World Health Organization) and the IUATLD (International Union Against Tuberculosis and Lung Disease) have established a global project of drug resistance surveillance that is based on standard epidemiological methods and quality control through an extensive network of reference laboratories. Accurate drug resistance surveillance data can be used to assess and improve national tuberculosis programs.

OBJECTIVE: To determine the clinical manifestations of patients with human immunodeficiency virus (HIV) infection and tuberculosis caused by multiple-drug-resistant bacilli compared with those with single-drug-resistant or susceptible bacilli. DESIGN: Descriptive, case-control, and cohort studies. SETTING: A large urban teaching hospital. PATIENTS: Sixty-two patients with tuberculosis caused by multiple-drug-resistant bacilli (cases) and 55 patients with tuberculosis caused by single-drug-resistant or susceptible bacilli (controls). MEASUREMENTS: Characteristics of clinical presentation, radiographs, pathologic abnormalities, antituberculosis treatment, and clinical course. RESULTS: Twenty cases (32%) had concomitant pulmonary and extrapulmonary disease at presentation compared with 9 controls (16%; odds ratio, 2.4; 95% CI, 1.0 to 5.9). More cases had alveolar infiltrates (76%; odds ratio, 3.6; CI, 1.2 to 11.4), interstitial infiltrates with a reticular pattern (67%; odds ratio, 7.8; CI, 1.0 to 83.5), and cavitations (18%; odds ratio, 6.6; CI, 0.8 to 315.3) on initial chest radiographs compared with controls (49%, 19%, and 3%, respectively). Pathologic specimens from cases showed extensive necrosis, poor granuloma formation, marked inflammatory changes with a predominance of neutrophils, and abundant acid-fast bacilli. Twenty-five cases received two or more effective antituberculosis drugs for more than 2 months. Only 2 cases had three consecutive negative cultures for Mycobacterium tuberculosis; one patient died within 1 day of the last negative culture, and the other had positive cultures 496 days later. The remaining 23 cases had persistently or intermittently positive cultures despite therapy. The clinical course of these cases suggested overwhelming miliary tuberculosis with involvement of the lungs (77%), pleura (15%), stool (34%), meninges (13%), bone marrow (16%), blood (10%), lymph nodes (10%), and skin (8%). The median survival time was 2.1 months for cases compared with 14.6 months for controls (P = 0.001, log-rank test). CONCLUSIONS: Tuberculosis caused by multiple-drug-resistant bacilli in patients with HIV infection is associated with widely disseminated disease, poor treatment response with an inability to eradicate the organism, and substantial mortality.

Progress in understanding the basis of resistance to isoniazid (INH) and rifampin (RMP) has allowed molecular tests for the detection of drug-resistant tuberculosis to be developed. Consecutive isolates (n = 95) of Mycobacterium tuberculosis, from a Spanish reference laboratory investigating outbreaks of multidrug-resistant tuberculosis, were coded and sent to two external laboratories for genotypic analysis of INH and RMP resistance by PCR-single-strand conformation polymorphism (SSCP) analysis of specific regions of four genes: part of the coding sequence of katG and the promoter regions of inhA and ahpC for INH and the RMP resistance region of rpoB. After correction for the presence of outbreak strains and multiple isolates from single patients, RMP resistance was detected successfully by PCR-SSCP in > 96% of the RMP-resistant strains. PCR-SSCP had a sensitivity of 87% for INH resistance detection, and mutations in katG, inhA, katG-inhA, ahpC, and katG-ahpC were identified in 36.8, 31.6, 2.6, 13.2, and 2.6%, respectively, of the unique strains. Specificity was 100%. Molecular detection of resistance to the two main antituberculous drugs, INH and RMP, can be accomplished accurately by using a strategy which limits analysis to four genetic regions. This may allow the expedient analysis of drug resistance by reference laboratories.

The molecular mechanisms of resistance to streptomycin, rifampin, and isoniazid in 53 Mycobacterium tuberculosis clinical isolates were examined. Twenty-five of 44 streptomycin-resistant strains had mutations in the rpsL gene and 5 of these had rrs gene perturbations. The region of the rpoB gene that is associated with resistance to rifampin was altered in 28 of 29 rifampin-resistant strains. Mutations in known genetic markers of isoniazid resistance were detected in 25 of 42 isoniazid-resistant isolates: 20 strains had katG gene alterations and 5 had perturbations in the inhA operon. Of the 20 multiply resistant strains with reduced sensitivity to streptomycin, rifampin, and isoniazid, 11 had mutations in genetic markers associated with resistance to each of these three drugs. These studies suggest that the primary mechanism of multiple drug resistance in tuberculosis is the accumulation of mutations in individual drug target genes.

The antimycobacterial compound ethambutol [Emb; dextro-2,2'-(ethylenediimino)-di-1-butanol] is used to treat tuberculosis as well as disseminated infections caused by Mycobacterium avium. The critical target for Emb lies in the pathway for the biosynthesis of cell wall arabinogalactan, but the molecular mechanisms for drug action and resistance are unknown. The cellular target for Emb was sought using drug resistance, via target overexpression by a plasmid vector, as a selection tool. This strategy led to the cloning of the M. avium emb region which rendered the otherwise susceptible Mycobacterium smegmatis host resistant to Emb. This region contains three complete open reading frames (ORFs), embR, embA, and embB. The translationally coupled embA and embB genes are necessary and sufficient for an Emb-resistant phenotype which depends on gene copy number, and their putative novel membrane proteins are homologous to each other. The predicted protein encoded by embR, which is related to known transcriptional activators from Streptomyces, is expendable for the phenotypic expression of Emb resistance, but an intact divergent promoter region between embR and embAB is required. An Emb-sensitive cell-free assay for arabinan biosynthesis shows that overexpression of embAB is associated with high-level Emb-resistant arabinosyl transferase activity, and that embR appears to modulate the in vitro level of this activity. These data suggest that embAB encode the drug target of Emb, the arabinosyl transferase responsible for the polymerization of arabinose into the arabinan of arabinogalactan, and that overproduction of this Emb-sensitive target leads to Emb resistance.