Abstract: This invention relates to the identification, cloning, sequencing and characterization of the embCAB operon which determines mycobacterial resistance to the antimycobacterial drug ethambutol. The embCAB operon encodes the proteins which are the target of action of Mycobacterium tuberculosis, Mycobacterium smegmatis, and Mycobacterium leprae for ethambutol. The present invention provides purified and isolated embC, embA, and embB nucleic acids which comprise the embCAB operon, as well as mutated forms of these nucleic acids. The present invention also provides one or more single-stranded nucleic acid probes which specifically hybridize to the wild type embCAB operon or the mutated embCAB operon, and mixtures thereof, which may be formulated in kits, and used in the diagnosis of drug-resistant mycobacterial strain. The present invention also provides methods for the treatment and prevention of mycobacterial infections.

Abstract: A process for the detection of resistance to an antibiotic in a mycobacterium comprises detecting a mutation in a gene selected from the group consisting of the katG gene or fragment thereof, the rpoB gene or fragment thereof, and the rpsI gene or fragment thereof. The process is useful for detecting in vitro the presence of nucleic acids of a Mycobacterium tuberculosis resistant to isoniazid.