Sulfonamide activity against Mycobacterium fortuitum and Mycobacterium chelonei

Forty-eight clinical strains of Mycobacterium fortuitum and 15 clinical strains of Mycobacterium chelonei were evaluated for susceptibility to sulfonamides, including trimethoprim-sulfamethoxazole (TMP-SMZ). Sensitivity tests were carried out with use of agar dilutions in Mueller-Hinton agar and a plate inoculum of 10(2) cfu. Thirty-six percent of the isolates of M. fortuitum were inhibited by 8 micrograms of sulfonamide/ml, and 98% were inhibited by 32 micrograms/ml. None of the isolates of M. chelonei were inhibited at these concentrations, but 73% were inhibited by 128 micrograms/ml, and 87% were inhibited by 256 micrograms/ml. Both species were highly resistant to TMP, and the combination TMP-SMZ (1:20) was no more active than was SMZ alone. The growth of M. chelonei on Mueller-Hinton agar required the addition of 10% OADC (oleic acid, albumin, dextrose, and catalase), and exact MICs were difficult to determine by agar dilutions because growth of the organism tended to diminish gradually over several dilutions. Six patients with disease due to rapidly growing mycobacteria were treated with sulfonamides, and all showed a good response to therapy. Sulfonamides may be the treatment of choice for infections due to M. fortuitum and offer potential for the therapy of disease due to M. chelonei.