title: Overexpression of the chromosomally encoded aminoglycoside acetyltransferase eis confers kanamycin resistance in Mycobacterium tuberculosis.
abstract: 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 microg/mL < minimum inhibitory concentration (MIC) <or=40 microg/mL] but not to amikacin (MIC <4 microg/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.
authors.affiliation: Microbiology and Molecular Genetics Graduate Program, Department of Microbiology and Immunology, Rollins Research Center, Emory University, Atlanta, GA 30322, USA.
authors.forename: M Analise
authors.initials: MA
authors.lastname: Zaunbrecher
authors.forename: R David
authors.initials: RD
authors.lastname: Sikes
authors.forename: Beverly
authors.initials: B
authors.lastname: Metchock
authors.forename: Thomas M
authors.initials: TM
authors.lastname: Shinnick
authors.forename: James E
authors.initials: JE
authors.lastname: Posey
mesh_terms: D000123:Acetyltransferases / Q000494:pharmacology / Q000627:therapeutic use; D000583:Amikacin / Q000494:pharmacology / Q000627:therapeutic use; D000900:Anti-Bacterial Agents / Q000494:pharmacology / Q000627:therapeutic use; D000942:Antigens, Bacterial / Q000235:genetics / Q000378:metabolism; D000995:Antitubercular Agents / Q000494:pharmacology / Q000627:therapeutic use; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism; D024901:Drug Resistance, Multiple, Bacterial / Q000502:physiology*; D006801:Humans; D007612:Kanamycin / Q000494:pharmacology / Q000627:therapeutic use; D008826:Microbial Sensitivity Tests; D009169:Mycobacterium tuberculosis / Q000187:drug effects / Q000201:enzymology / Q000502:physiology; D011401:Promoter Regions, Genetic; D014158:Transcription, Genetic; D018088:Tuberculosis, Multidrug-Resistant / Q000188:drug therapy / Q000201:enzymology / Q000235:genetics
chemical_list: D000900:Anti-Bacterial Agents; D000942:Antigens, Bacterial; D000995:Antitubercular Agents; D001426:Bacterial Proteins; D007612:Kanamycin; D000583:Amikacin; D000123:Acetyltransferases; C430563:Eis protein, Mycobacterium tuberculosis; C019681:aminoglycoside acetyltransferase