Due to the slow growth and relative resistance of mycobacteria to many antimicrobial agents, drug susceptibility testing (DST) has been technically difficult in the past, and is now mostly performed in regional reference laboratories.
Currently, phenotypic DST for Mycobacterium tuberculosis is performed using a semi‐automated broth culture system under internationally standardised protocols. With rising rates of drug resistance being reported worldwide, all new (and potential relapse) isolates of M. tuberculosis should be tested against first‐line anti‐tuberculous agents, and should any resistance be detected, representative second line agents should also be tested.
DST methods are well established for several other mycobacterial species, but are of limited value in some, especially the M. avium complex (MAC).
Recently commercial assays have started appearing that directly detect resistance mutations in M. tuberculosis genes encoding anti‐tuberculous drug targets. Advantages and limitations of this approach will be discussed.