Susceptibility testing of the non-tuberculous mycobacteria

In vitro susceptibility test criteria have been defined for only a limited number of non-tuberculous mycobacteria (NTM) because definitive studies correlating in vivo outcomes with in vitro data are lacking. Another contributing factor is the assigning of a pathogenic role to the isolation of a particular NTM. Currently, clarithromycin susceptibility testing of clinically significant Mycobacterium avium complex (MAC) isolates is recommended. However, breakthrough isolates of MAC have been shown to exhibit elevated MICs to other agents the patients were receiving. More data exist with testing isolates of Mycobacterium kansasii, which can be tested in a fashion similar to that for isolates of Mycobacterium tuberculosis. There are limited recommendations for other species of slowly growing mycobacteria. Testing of rapidly growing species of mycobacteria against antibacterial agents has been shown to have some clinical utility. The methods used to perform this testing also need to be further validated.