Materials and Methods: Matrix-assisted laser desorption ionization time of flight mass spectrometry (MALDI-TOF MS) has been recently introduced as a novel technique for identifying microbial pathogens. However, the characterization of bacterial drug resistance by MALDI-TOF MS assay has rarely been studied. This work was performed to characterize drug-resistant M. tuberculosis strains using classical antibiogram, molecular, and MALDI-TOF MS assays. Pathogenic M. tuberculosis strains were isolated by culturing clinical specimens in Löwenstein–Jensen medium and identified by amplification of IS6110. Drug resistance was characterized using classical antibiogram, sequencing of the rpoB, gyrA, katG, and rrs genes, and analyzing the MALDI-TOF MS spectrograms of bacterial cell wall components.

Results: The highest resistance was observed for capreomycin and ciprofloxacin (48%), followed by isoniazid (42%). Sequencing of drug target genes showed that point mutations at codons 507 of rpoB,315 of katG, 284 of gyrA, and 1260 of rrs genes were the major molecular causes of resistance to Rifampin, Ethambutol, Ciprofloxacin, and Kanamycin, respectively.

Conclusions: The MALDI-TOF MS assay revealed that bacterial strains have different spectrograms based on their drug resistance phenotypes. Therefore, this work revealed that the MALDI-TOF MS assay could be considered a novel and rapid technique to characterize the drug resistance pattern of M. tuberculosis.