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.