No abstract

The SLOMYCO Sensititre panel and the custom JustOne strip (both from TREK Diagnostic Systems, Cleveland, OH) were evaluated for susceptibility testing of Mycobacterium avium complex isolates against clarithromycin. Seventy-one archived and prospectively collected isolates were tested using both the SLOMYCO panel and the JustOne strip, and the results were compared to those obtained using the BACTEC 460 (BD, Sparks, MD) radiometric method and a broth microdilution reference method. Results obtained by the SLOMYCO panel and the JustOne strip agreed with the BACTEC 460 method for 64/71 isolates (90%). Similarly, concordance with the broth microdilution method was 40/43 isolates (93%) for both test systems. The effect of the source medium on inoculum preparation was evaluated, and there were no differences noted in MICs, regardless of whether the inoculum was prepared from isolates grown in Middlebrook 7H9 medium, on Middlebrook 7H10 agar, or in VersaTREK broth culture bottles (Trek Diagnostics). Clarithromycin susceptibility testing of MAC using the SLOMYCO panel and the JustOne strip methods is easy to set up and simple to read and is readily incorporate into the clinical laboratory. These systems offer advantages over the BACTEC 460 system including the lack of a need for radioactive substrates, sharps, or costly instrumentation.Nontuberculous mycobacteria (NTM) are increasingly recognized as a cause of pulmonary disease (1), and some of the most common NTM species isolated in the clinical laboratory are members of the Mycobacterium avium complex (MAC). In addition to pulmonary disease, MAC infection can result in lymphadenitis and disseminated disease in both immunocompromised and immunocompetent patients (9). The American Thoracic Society (ATS) and the Infectious Diseases Society of America (IDSA) recommend that a three-drug regimen be utilized for the treatment of MAC infection, including a macrolide (clarithromycin or azithromycin), ethambutol, and a rifamycin such as rifampin (4).The ATS and the IDSA recommend performing susceptibility testing of MAC isolates only against the macrolides based on the results of the limited number of available, well-controlled clinical trials correlating in vitro susceptibility data and clinical outcomes (2,3,6). The ATS, the IDSA, and the Clinical and Laboratory Standards Institute (CLSI) all recommend that susceptibility testing of MAC be performed for the initial clinical isolate, for isolates from patients previously on macrolide therapy, for isolates from patients failing macrolide therapy, for isolates from AIDS patients who develop bacteremia while on macrolide prophylaxis, and for isolates from patients with positive blood cultures after 3 months of therapy for disseminated MAC infection (4, 5). The CLSI guideline also suggests that clarithromycin can serve as a class drug for azithromycin and that therefore only clarithromycin needs to be routinely tested. Although some experts disagree, testing of drugs other than clarithromycin is not recommended at this time since ...