We evaluated the in vitro activities of tigecycline and 10 other antibiotics against clinical isolates of nonpigmented rapidly growing mycobacteria. Fifteen collection strains and 165 clinical isolates were included in the study. Tigecycline showed the highest activity among all antibiotics studied: all the strains were inhibited by 1 mg/liter.Nonpigmented rapidly growing mycobacteria (NPRGM) constitute a group of species of the genus Mycobacterium that share some characteristics. They are among the most commonly isolated species in clinical mycobacteriology laboratories (7). NPRGM, especially the nonrespiratory isolates (5), cause human infections (3, 4). Due to differences between strains, these organisms require individualized treatment that needs to be selected on the basis of results obtained from in vitro susceptibility tests. New antibiotics have been added to those previously recognized as active against these species, such as linezolid (12) or telithromycin (6). Tigecycline is a new antibiotic that has good activity against some of these species (11). However, because regional differences can exist, moredetailed studies with NPRGM from different areas are required. Here we report a study of the susceptibilities of NPRGM to tigecycline and other antimicrobials used for the treatment of infections caused by these organisms.Fifteen , and M. septicum [n ϭ 1]) of NPRGM were included in the study. The clinical isolates were from the area of Madrid, Spain, and were collected from 1990 to 2006. They were identified using a combination of standard biochemical tests and PCR with restriction fragment length polymorphism analysis (10). Strains were maintained frozen at Ϫ20°C until the study was performed. Prior to testing, strains were subcultured, checked for purity, and reidentified.The following antibiotics were used in the study: tigecycline (Wyeth, Madison, NJ), levofloxacin (GSK, Brentford, United Kingdom), cefoxitin, ciprofloxacin, amikacin, tobramycin, doxycycline, cotrimoxazole, erythromycin (Sigma, St. Louis, MO), azithromycin (Pfizer, New York, NY), and clarithromycin (Abbott, Abbott Park, IL).MICs were determined by the broth microdilution technique (8). Mycobacteria were grown on tryptic soy (5%) sheep blood agar (bioMérieux, Marcy l'Étoile, France) and incubated at 35°C for 4 days in room air. The inoculum was prepared directly from blood agar plates in cation-supplemented MuellerHinton broth (Difco, Detroit, MI) with 0.02% Tween 80 (Difco, Detroit, MI). Double dilutions of antibiotics were prepared and added to the wells at concentrations ranging from 64 to 0.03 g/ml. After inoculation, the plates were incubated at 30°C in room air and read at 3 days. Escherichia coli ATCC 25922, Staphylococcus aureus ATCC 29213, and Enterococcus faecalis ATCC 29212 were used as controls. Table 1 shows the results of the study. For the species with Ն10 strains tested, the MIC at which 50% of strains were inhibited (MIC 50 ), MIC 90 , and range are shown. For the strains with Ͻ10 strains tested, only the MIC range is ...
