The present invention provides a diagnostic test method for detecting a tendency to rifampin resistance caused by mutations in a rpoB gene of M. tuberculosis, comprising the steps of (i) extracting genomic DNA from a biological sample containing M. tuberculosis cells; (ii) amplifying from the extracted genomic DNA the rpoB gene coding sequence or at least one distinct fragment thereof containing nucleotides encoding at least one test amino acid of the group consisting of amino acid numbers 511, 512, 513, 514, 515, 516, 517, 518, 522, 526, 529, 531, 533 to produce fluorescently labeled amplification product; (iii) contacting said fluorescently labeled amplification product with a first control array of oligonucleotide probes having DNA sequences specific to the wildtype M. tuberculosis rpoB gene coding sequence, including the nucleotides encoding the at least one test amino acid, and with a second test array of oligonucleotide probes having DNA sequences specific to the M. tuberculosis rpoB gene coding sequence, including nucleotides encoding mutations in the at least one test amino acid, wherein at least 3 mutations of the rpoB gene are probed for by the second test array of oligonucleotide probes; detecting any fluorescent hybridization signal of said purified fluorescently labeled amplification product which hybridized with the first and second arrays of oligonucleotide probes; (iv) correlating said detected hybridization with a tendency to rifampin resistance; and (v) correlating the detected hybridization to a tendency to rifampcin resistance and MDR.