Catheter sepsis due to Mycobacterium chelonae.

We read with interest the recent article by Hsueh et al. on catheter sepsis due to Mycobacterium chelonae (3). In the antimicrobial susceptibility section, the clarithromycin MIC is reported to be 1.5 to 2.0 mg/ml. The authors later state, “. . . our isolates were not susceptible to any of the antibiotics tested, including clarithromycin.” In another study (1), which found 100% of M. chelonae isolates to be susceptible to #1.0 mg of clarithromycin per ml (by a different susceptibility method), resistance is defined as .4 mg/ml. This breakpoint for rapidly growing mycobacteria, although not approved by the National Committee for Clinical Laboratory Standards (NCCLS), has been proposed (2). Thus, we would consider these isolates to be susceptible to clarithromycin and suspect the somewhat higher MICs than reported by Hsueh et al. (3) could be method dependent (E test versus broth microdilution). Thus, clarithromycin likely contributed to the clinical and microbiologic response of the patient.