SUSCEPTIBILITY TESTING FOR RAPIDLY GROWING MYCOBACTERIA

​For mycobacteria isolated in CTBL or in other laboratories

​Isolates identified in referring labs must specify the organism’s identification and clinical source on the lab request form. For further instructions on packing, refer under IDENTIFICATION OF MYCOBACTERIA.

​Microbroth dilution

​Susceptible, Intermediate, Resistant, according to CLSI interpretive criteria

​1 - 2 weeks

​Once a week

​Drugs tested: Amikacin, cefoxitin, ciprofloxacin, clarithromycin*, doxycycline, imipenem**, linezolid, tobramycin***, trimethoprim-sulfamethoxazole, moxifloxacin, tigecycline and clofazimine. There are no CLSI interpretative criteria for tigecycline and clofazimine.

*Class representative for newer macrolides e.g. azithromycin. For the detection of the erm gene which causes inducible resistance to macrolides, a preliminary result is issued if the isolate is susceptible after Day 5 of incubation, followed by a final result after Day 14.

Identification of M. abscessus to the subspecies level (M. abscessus subsp abscessus, M. abscessus subsp massiliense, and M. abscessus subsp bolletti) will be performed as a reflex test because the resistance mechanisms and profiles may vary according to the subspecies. 

 ** Not predictive of results for meropenem or ertapenem as the activity against rapidly growing mycobacteria is greater for imipenem than for meropenem or ertapenem.

***M. chelonae from eye cultures only.