We compared the in vitro activity of the glycylcycline tigecycline (formerly GAR-936) with those of tetracycline, doxycycline, and minocycline by broth microdilution against 76 isolates belonging to seven species of rapidly growing mycobacteria (RGM) and 45 isolates belonging to five species of slowly growing nontuberculous mycobacteria (NTM). By using a resistance breakpoint of >4 g/ml for tigecycline and >8 g/ml for tetracycline, all RGM were highly susceptible to tigecycline, with inhibition of 50% of isolates at <0.12 g/ml and inhibition of 90% of isolates at 0.25 g/ml for Mycobacterium abscessus and inhibition of both 50 and 90% of isolates at <0.12 g/ml for M. chelonae and the M. fortuitum group. The MICs of tigecycline were the same for tetracycline-resistant and -susceptible strains, and RGM isolates were 4-to 11-fold more susceptible to tigecycline than to the tetracyclines. In contrast, no slowly growing NTM were susceptible to tigecycline, and isolates of M. marinum and M. kansasii were less susceptible to this agent than to minocycline. This new antimicrobial offers exciting therapeutic potential for the RGM, especially for isolates of the M. chelonae-M. abscessus group, against which the activities of the currently available drugs are limited.Treatment of infections due to rapidly growing mycobacteria (RGM) remains difficult, in part because of resistance to the first-line antituberculous agents and also in part because of resistance to almost all antibacterial agents (3, 21). The only drugs with activity against all three major pathogenic species (Mycobacterium chelonae, M. abscessus, and M. fortuitum) are amikacin (13) and clarithromycin (4). In vitro studies with prior glycylcyclines (N,N-dimethylglycylamido-minocycline ) have shown this class of agents to be extremely active against this group of organisms, including tetracycline-resistant strains (1, 3). The latest glycylcycline, tigecycline (GAR-936), has shown excellent activity against many tetracycline-resistant bacterial species (1, 8, 17; R. N. Jones, A. C. Gales, L. M. Deshpande, D. M. Johnson, and D. J. Biedenbach, poster 407, 39th Intersci. Conf. Antimicrob. Agents Chemother., 1999). With this in mind, we undertook a comparative study of the in vitro susceptibilities of multiple species of nontuberculous mycobacteria (NTM) to tetracycline, minocycline, doxycycline, and tigecycline.(A portion of this study was presented at the 41st Interscience Conference on Antimicrobial Agents and Chemotherapy, 16 to 19 December 2001, Chicago, Ill.) MATERIALS AND METHODSOrganisms. Clinical mycobacterial isolates submitted to the Mycobacterial/ Nocardia Laboratory at The University of Texas Health Center for susceptibility testing and selected reference strains were chosen for testing. Clinical isolates were tested upon receipt in the laboratory, while the reference strains were taken from frozen stocks stored at Ϫ70°C in Trypticase soy broth with 15% glycerol. We also tested 45 isolates of slowly growing NTM that included 11 M. avium complex, 10 M. ...

Linezolid is an oxazolidinone available as an oral drug which has activity against most gram-positive bacteria. However, few species of the genus Mycobacterium have been studied. We tested 249 clinical isolates and 10 reference strains of rapidly growing mycobacteria for susceptibility to linezolid by broth microdilution. Clinical species included the Mycobacterium fortuitum group (n ‫؍‬ 74), M. abscessus (n ‫؍‬ 98), M. chelonae (n ‫؍‬ 50), M. mucogenicum (n ‫؍‬ 10), and M. fortuitum third biovariant complex (10). The modal MIC for M. mucogenicum was 1.0 g/ml, and the MIC at which 90% of the isolates tested are inhibited (MIC 90 ) was 4 g/ml; the modal MIC for the M. fortuitum group was 4 g/ml, and the MIC 90 was 16 g/ml; the modal MIC for the M. fortuitum third biovariant complex was 4 g/ml, and the MIC 90 was 8 g/ml; the modal MIC for M. chelonae was 8 g/ml, and the MIC 90 was 16 g/ml; and the modal MIC for M. abscessus was 32 g/ml, and the MIC 90 was 64 g/ml. Based on peak levels of linezolid in serum of 15 to 20 g/ml, we propose the following broth MIC breakpoints for these species: susceptible, < 8 g/ml; moderately susceptible, 16 g/ml; and resistant, >32 g/ml). These studies demonstrate the excellent potential of linezolid for therapy of rapidly growing mycobacteria.Treatment of infections due to nontuberculous mycobacteria remains difficult, in part because they are resistant to many of the first-line tuberculosis agents and in part because so few other agents are available for therapy (21 , abstr. 1098, 1999) which have the potential for activity against nontuberculous mycobacteria, including the rapidly growing mycobacteria (6; M. Wu, P. Aralor, K. Nash, L. E. Bermudez, C. B. Inderlied, and L. S. Young, Abstr. 38th Intersci. Conf. Antimicrob. Agents Chemother., abstr. E-143, 1998; L. E. Bermudez, Abstr. Int. Conf. Macrolides, Azalides, Streptogramins, Ketolides and Oxazolidinone, abstr. 03.16, 2000).We chose to study linezolid, which along with eperezolid is the first of the oxazolidinones to reach clinical testing (4; M. C. Birmingham et al., 39th ICAAC) Linezolid offers special promise, as it is a twice-daily oral drug which is 100% bioavailable (Zyvox package insert, 2000 [Pharmacia & Upjohn, Inc.]; also see reference 8) and appears to be well tolerated (8; N. E. Wilks, Abstr. 39th Intersci. Conf. Antimicrob. Agents Chemother., abstr. 1763Chemother., abstr. , 1999, important features of therapeutic drugs to be used against nontuberculous mycobacteria which cause chronic infections and require long-term therapy (often 6 months or longer) (21). The activities of linezolid against a large number of clinical isolates of rapidly growing mycobacteria, including the common disease-producing species Mycobacterium fortuitum, M. chelonae, and M. abscessus (24), were studied.(This work was presented in part as an abstract at the 100th General Meeting of the American Society for Microbiology, Los Angeles, Calif.) T , and M. abscessus ATCC 19977 T . Susceptibility testing. Susceptibility testing utilized seri...

Six clinical isolates of the nonpigmented, rapidly growing species Mycobacterium mageritense were recovered from sputum, bronchial wash, blood, sinus drainage, and two surgical wound infections from separate patients in Texas, New York, Louisiana, and Florida. The isolates matched the ATCC type strain by PCR restriction enzyme analysis of the 65-kDa hsp gene sequence of Telenti, high-performance liquid chromatography, biochemical reactions, and partial 16S rRNA gene sequencing. These are the first isolates of this species to be described in the United States and the first isolates to be associated with clinical disease. Susceptibility testing of all known isolates of the species revealed all isolates to be susceptible or intermediate to amikacin, cefoxitin, imipenem, and the fluoroquinolones and sulfonamides but resistant to clarithromycin. Because of their phenotypic and clinical similarity to isolates of the Mycobacterium fortuitum third biovariant complex (sorbitol positive), isolates of M. mageritense are likely to go undetected unless selected carbohydrate utilization or molecular identification methods are used.In 1997 Domenech et al. (4) described a new nonpigmented species of rapidly growing mycobacterium that they named Mycobacterium mageritense. The name was derived from Magerit, the old Arabic name of Madrid, where four of the five isolates had been recovered. The isolates were from sputum and came from two hospitals in Spain. None were known to be clinically significant. The isolates were nonpigmented and had similarities to both M. smegmatis and the M. fortuitum complex (1, 4, 10, 18).Utilizing PCR restriction enzyme analysis (PRA) of the Telenti fragment (11, 14) of the 65-kDa hsp gene, we identified six clinical isolates whose PRA patterns matched the pattern of M. mageritense. We compared these strains to the initial strains from Spain by using standard growth and biochemical tests, partial 16S rRNA gene sequencing, PRA of the 65-kDa hsp gene, high-performance liquid chromatography (HPLC), and determination of antimicrobial susceptibilities. Growth and biochemical characterization. All 11 isolates identified as M. mageritense were examined for colony morphology, pigmentation, and growth within 7 days on Trypticase soy agar and Middlebrook 7H10 agar at 30, 35, and 45°C, as well as for arylsulfatase activity at 3 days (graded from 0 to 4ϩ), nitrate reductase activity (graded from 0 to 5ϩ), iron uptake, and urease activity (graded from 0 to 4ϩ) (5). Carbohydrate utilization testing included D-mannitol, i-myoinositol, citrate, D-galactose, L-rhamnose, D-trehalose, D-glucitol (sorbitol), Dxylose, and L-arabinose (10, 15). Acetamide (Becton Dickinson Biosciences, Sparks, Md.) utilization was also determined in addition to susceptibility to kanamycin, cephalothin, and polymyxin B by using a disk diffusion technique on Mueller-Hinton agar (17,20). MATERIALS AND METHODS OrganismsSusceptibility testing. Susceptibility to 10 antimicrobial agents was determined by broth microdilution in cation-supplemented M...

Linezolid was tested by broth microdilution against 140 clinical Nocardia isolates belonging to seven species. The MIC at which 50% of the strains are inhibited (MIC 50 ) and MIC 90 for all species other than Nocardia farcinica were 2 and 4 g/ml. Linezolid is the first antimicrobial agent demonstrated to be active against all Nocardia species.Treatment of Nocardia infections continues to be difficult, especially with central nervous system or disseminated disease (1,6,7,9,10) and species, such as Nocardia farcinica, that are highly drug resistant (22). Most recent antimicrobial therapy of complicated cases has involved the use of a sulfonamide or trimethoprim-sulfamethoxazole plus the injectable agents amikacin and imipenem or ceftriaxone (6,10,16,18 E-143, 1998.). We studied the new oxazolidinone compound linezolid against all clinically important species of Nocardia including drug-resistant species, such as N. farcinica and Nocardia transvalensis (22,23).(Presented in part at the 99th Annual Meeting of the American Society for Microbiology, Los Angeles, Calif., May 2000.)Linezolid is a new class of synthetic antibiotics which prevent protein synthesis by blocking the formation of a function initiation complex (9, 11). The exact mechanism of action is unique, and no cross-resistance has been discovered in strains of bacteria resistant to other antimicrobial agents (11).We tested 192 clinical Nocardia isolates submitted for susceptibility testing from January 1999 through January 2000 to the Mycobacteria/Nocardia Research Laboratory at The University of Texas Health Center for their susceptibility to linezolid. Isolates from 27 states and Mexico were tested, with 60% of the isolates from Texas, Florida, North Carolina, Ohio, Massachusetts, and Connecticut. Approximately 40% of the organisms were identified to the species level by PCR restriction analysis of the 439-bp Telenti segment of the 65-kDa hsp gene (13)(14)(15)(16)23), and all were identified by their patterns of susceptibility (16,17,(20)(21)(22)(23) to approximately 15 other drugs, including aminoglycosides, beta lactams, and quinolones. The test isolates belonged to seven species (eight taxa) and included Nocardia asteroides sensu stricto (n, 34), N. farcinica (n, 25), Nocardia brasiliensis (n, 24), Nocardia nova (n, 41), Nocardia pseudobrasiliensis (n, 8), Nocardia otitidiscaviarum (n, 5), N. transvalensis complex (n, 7), and Nocardia sp. (n, 2).Susceptibility testing utilized three methods. The first was serial twofold broth microdilution in cation-supplemented Mueller-Hinton broth as previously described and recently approved by the NCCLS (4, 24). The second was the E-test (2) (generously supplied by Pharmacia and Upjohn, Inc., and AB Biodisks) performed on selected isolates on Mueller-Hinton agar using a 1-McFarland standard inoculum. The third method was agar disk diffusion (20, 21) performed with Mueller-Hinton agar and 30-g linezolid disks generously supplied by the manufacturer, Pharmacia and Upjohn, Inc. Susceptibilities to linezolid by all ...

We describe a 57-year-old man with steroid-dependent myasthenia gravis and progressive ulcerating leg nodules due to clarithromycin-resistant Mycobacterium chelonae. The patient was successfully treated with linezolid.

The rapidly growing mycobacterial species Mycobacterium porcinum was described in 1983 by Tsukamura et al. as a causative agent of submandibular lymphadenitis in swine (23). Tsukamura et al. characterized these strains as being similar to M. fortuitum but differing from this species by being D-mannitol and i-myo-inositol positive, nitrate negative, and succinamidase positive and utilizing benzoate as a sole source of carbon in the presence of ammoniacal nitrogen. Until recently, no isolation of this species had been reported since that report.Bönicke studied isolates previously identified as M. fortuitum and placed them into three subgroups (1). Subgroup A was negative for D-mannitol and i-myo-inositol and now is recognized as M. fortuitum. Subgroup B was positive for D-mannitol but negative for i-myo-inositol and is now recognized as M. peregrinum. Subgroup C was positive for mannitol and inositol, and its taxonomic status has taken much longer to establish and is still evolving. A study by Wallace et al. in 1991 showed this subgroup to consist of two major groups. One group was D-sorbitol positive, had low semiquantitative catalase, and was pipemidic acid resistant, and MICs of cefoxitin (27) and clarithromycin (4) were high for members of the group. ␤-Lactamase patterns on polyacrylamide gels following isoelectric focusing (IEF) had previously showed these isolates to have primarily a single enzyme pattern (28). These isolates were named the M. fortuitum third biovariant complex D-sorbitol-positive group, and ATCC 49403 was chosen as the reference strain (27).Subsequent 16S rRNA gene sequencing showed these isolates to have a unique hypervariable A region (11,19) and an 880-bp sequence of ATCC 49403 to differ by 6 to 15 bp from previously recognized species within the M. fortuitum group (11). To date, three species are recognized within this D-sorbitol-positive group based on 16S rDNA complete sequencing and DNA-DNA homology studies: M. mageritense (7,26), M. houstonense (of which ATCC 49403 is the proposed type strain), and M. brisbanense (16).

MICs of linezolid in broth microdilutions were tested against 341 slowly growing nontuberculous mycobacteria (NTM) belonging to 15 species. The proposed linezolid susceptibility MICs for all Mycobacterium marinum, Mycobacterium szulgai, Mycobacterium kansasii, Mycobacterium malmoense, and Mycobacterium xenopi isolates and for 90% of Mycobacterium gordonae and Mycobacterium triplex isolates were <8 g/ml. Linezolid has excellent therapeutic potential against most species of NTM.Treatment of infections due to slowly growing nontuberculous mycobacteria (NTM) remains difficult for many species. In some cases only a few drugs are available for therapy, and in most situations combination therapy is necessary. Previous in vitro studies with linezolid have shown it to be active against most species of rapidly growing mycobacteria (RGM) (11) and Nocardia (4) and recently against Mycobacterium tuberculosis (1) at readily achievable levels in serum. Thus, we undertook a study of the in vitro activity of linezolid against species of slowly growing NTM.(This work was presented in part at the 42nd Interscience Conference on Antimicrobial Agents and Chemotherapy, San Diego, Calif., 27 to 30 September 2002.)We tested linezolid against 341 isolates of slowly growing NTM belonging to 15 species. This number included 335 clinical strains submitted for susceptibility testing and/or identification and six reference isolates kindly provided by the American Type Culture Collection (ATTC). The isolates included those of the Mycobacterium avium complex (MAC) (189 isolates), Mycobacterium marinum (47 isolates), Mycobacterium szulgai (10 isolates), Mycobacterium gordonae (21 isolates), Mycobacterium kansasii (19 isolates), Mycobacterium simiae complex (15 isolates), Mycobacterium terrae complex (11 isolates), Mycobacterium triplex (10 isolates), Mycobacterium lentiflavum (5 isolates), Mycobacterium xenopi (5 isolates), Mycobacterium malmoense (5 isolates), and one isolate each of Mycobacterium interjectum, Mycobacterium asiaticum, Mycobacterium scrofulaceum, and Mycobacterium branderi. Susceptibility was determined once for each isolate except for some reference strains.The isolates were identified by standard methods, including a combination of traditional biochemicals and high-performance liquid chromatography (2, 6; S. H. Chiu, K. C. Jost, Jr., D. F. Dunbar, and L. B. Elliott, Abstr. 98th Gen. Meet. Am. Soc. Microbiol. 1998, abstr. U-76, p. 508, 1998), nucleic acid probes, (5) or PCR-restriction fragment length polymorphism analysis of the 439-bp Telenti fragment of the 65-kDa hsp gene (9, 10). Most isolates of the MAC were identified by highperformance liquid chromatography and/or nucleic acid probes. All species other than those of the MAC, M. kansasii, M. marinum, and M. gordonae were confirmed by PCR-restriction fragment length polymorphism analysis.MICs were determined by using NCCLS-recommended serial twofold broth microdilutions in cation-adjusted MuellerHinton broth (12). MICs were tested with multiple lots of plates with linezo...

By using current NCCLS broth microdilution methods, we found that gatifloxacin inhibited 90% of the isolates of the Mycobacterium fortuitum group at <0.12 g/ml and 90% of the Mycobacterium chelonae isolates at <4 g/ml. Gatifloxacin was generally fourfold more active than ciprofloxacin. We recommend that both gatifloxacin and ciprofloxacin be tested routinely against rapidly growing mycobacteria.The fluoroquinolones have become increasingly important in the treatment of infections due to mycobacteria. Previous studies involving a wide variety of clinical bacterial isolates and the new 8-methoxy quinolone, gatifloxacin, have shown that gatifloxacin is more active than ciprofloxacin against untreated strains (1, 5) and that its activity (MIC) is less affected overall by mutations responsible for increasing quinolone resistance. Thus, we undertook a comparative study of the in vitro susceptibilities of the rapidly growing mycobacteria (RGM) to gatifloxacin and ciprofloxacin.(A portion of this study was presented at the 41st RGM were identified by using conventional methods, including drug susceptibility patterns (15), carbohydrate utilization tests, and PCR restriction enzyme analysis of a 439-bp sequence (Telenti fragment) of the 65-kDa hsp gene (8, 10).MICs were determined by use of the NCCLS-approved broth microdilution technique (6, 7). MICs of gatifloxacin were 0.12 to 32 g/ml, while those of ciprofloxacin were 0.12 to 16 g/ml (one lot number of panels used contained concentrations of ciprofloxacin of Յ0.25 to 16 g/ml). The MIC breakpoints indicating susceptibility, moderate susceptibility (intermediate), and resistance to gatifloxacin were Յ2, 4, and Ն8 g/ml, and those for ciprofloxacin were Յ1, 2, and Ն4 g/ml (the NCCLS breakpoints for Enterobacteriaceae and Staphylococcus species) (6). Gatifloxacin breakpoints for RGM have not yet been addressed by the NCCLS (7).For quality control tests, Staphylococcus aureus ATCC 29213 and Escherichia coli ATCC 25922 were used. Acceptable MIC ranges for S. aureus ATCC 29213 are 0.03 to 0.12 and 0.12 to 0.5 g/ml for gatifloxacin and ciprofloxacin, respectively. Acceptable MIC ranges for E. coli ATCC 25922 are 0.008 to 0.03 and 0.004 to 0.016 g/ml for gatifloxacin and ciprofloxacin, respectively (6).Results for the major species (groups) of pathogenic RGM are shown in Tables 1 and 2. Generally, the MICs of gatifloxacin for all of the RGM except M. abscessus were 1 to 4 dilutions lower than those of ciprofloxacin.