The emergence of multidrug-resistant (MDR) tuberculosis (TB) highlights the urgent need to understand the mechanisms of resistance to the drugs used to treat this disease. The aminoglycosides kanamycin and amikacin are important bactericidal drugs used to treat MDR TB, and resistance to one or both of these drugs is a defining characteristic of extensively drug-resistant TB. We identified mutations in the ؊10 and ؊35 promoter region of the eis gene, which encodes a previously uncharacterized aminoglycoside acetyltransferase. These mutations led to a 20 -180-fold increase in the amount of eis leaderless mRNA transcript, with a corresponding increase in protein expression. Importantly, these promoter mutations conferred resistance to kanamycin [5 g/mL < minimum inhibitory concentration (MIC) <40 g/mL] but not to amikacin (MIC <4 g/mL). Additionally, 80% of clinical isolates examined in this study that exhibited low-level kanamycin resistance harbored eis promoter mutations. These results have important clinical implications in that clinical isolates determined to be resistant to kanamycin may not be cross-resistant to amikacin, as is often assumed. Molecular detection of eis mutations should distinguish strains resistant to kanamycin and those resistant to kanamycin and amikacin. This may help avoid excluding a potentially effective drug from a treatment regimen for drug-resistant TB.T he World Health Organization estimates that 9.2 million new cases of tuberculosis (TB) occur each year (1). Despite intensive efforts to ensure proper drug dosages and patient compliance with drug regimens, multidrug-resistant (MDR) and extensively drug-resistant (XDR) strains of Mycobacterium tuberculosis have emerged (2). These strains cause extensive mortality in immunocompromised individuals (3) and hinder the control and prevention of the disease. XDR and MDR TB infections cannot be adequately treated with the first-line anti-TB drugs and require expensive, prolonged treatment with second-line anti-TB drugs. The rapid determination of the resistance profile of an isolate can facilitate selection of an appropriate drug regimen and preclude development of additional drug resistances. Rapid detection of resistances is best achieved with molecular diagnostic approaches, particularly in developing countries where access to culture facilities is limited. Such strategies require a detailed understanding of the molecular basis for drug resistance. Although the mechanisms of resistance to first-line drugs such as isoniazid and rifampin are well characterized, much less is known about such mechanisms for the second-line drugs (4).An important second-line anti-TB drug is the aminoglycoside kanamycin (KAN), which binds to the 16S rRNA in the 30S ribosomal subunit and inhibits protein synthesis (5). In other bacteria, characterized mechanisms of KAN resistance include altered efflux or influx of the drug, inactivation of the drug by enzymatic modification, and mutation or methylation of rRNA, which disrupts binding of the drug to the riboso...

The lengthy course of treatment with currently used anti-mycobacterial drugs and the resulting emergence of drug-resistant strains have intensified the need for alternative therapies against Mycobacterium tuberculosis (Mtb), the etiologic agent of tuberculosis. We show that Mtb and Mycobacterium marinum use Abl and related tyrosine kinases for entry and intracellular survival in macrophages. In mice, the Abl-family tyrosine kinase inhibitor, imatinib (Gleevec®), when administered prophylactically or therapeutically, reduced both the number of granulomatous lesions and bacterial load in infected organs, and was also effective against a rifampicin-resistant strain. Further, when co-administered with current first-line drugs, rifampicin or rifabutin, imatinib acted synergistically. These data implicate host tyrosine kinases in entry and intracellular survival of mycobacteria, and suggest that imatinib may have therapeutic efficacy against Mtb. Because imatinib targets host, it is less likely to engender resistance compared to conventional antibiotics, and may decrease the development of resistance against co-administered drugs.

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