Antibiotic resistance
Antibiotic resistance in "M. tuberculosis" typically occurs due to either the accumulation of mutations in the genes targeted by the antibiotic or a change in titration of the drug. "M. tuberculosis" is considered to be multidrug-resistant (MDR TB) if it has developed drug resistance to both rifampicin and isoniazid, which are the most important antibiotics used in treatment. Additionally, extensively drug-resistant "M. tuberculosis" (XDR TB) is characterized by resistance to both isoniazid and rifampin, plus any fluoroquinolone and at least one of three injectable second-line drugs (i.e., amikacin, kanamycin, or capreomycin).