Mycobacterium immunogenum sp. nov., a novel species related to Mycobacterium abscessus and associated with clinical disease, pseudo-outbreaks and contaminated metalworking fluids: an international cooperative study on mycobacterial taxonomy.

PCR-restriction enzyme pattern analysis of a 439 bp hsp65 gene segment identified 113 unique isolates among non-pigmented rapidly growing mycobacteria (RGM) from clinical and environmental sources that failed to match currently recognized species patterns. This group represented 40% of isolates recovered from bronchoscope contamination pseudo-outbreaks, 0% of disease-associated nosocomial outbreaks and 4% of routine clinical isolates of the Mycobacterium abscessus/Mycobacterium chelonae group submitted to the Mycobacteria/Nocardia laboratory for identification. It is grouped within the Mycobacterium fortuitum complex, with growth in less than 7 d, absence of pigmentation, positive 3-d arylsulfatase reaction and growth on MacConkey agar without crystal violet. It exhibited overlapping biochemical, antimicrobial susceptibility and HPLC characteristics of M. abscessus and M. chelonae. By 16S rRNA gene sequencing, these isolates comprised a homogeneous group with a unique hypervariable region A sequence and differed by 8 and 10 bp, respectively, from M. abscessus and M. chelonae. Surprisingly, this taxon contained two copies of the ribosomal operon, compared with single copies in the two related species. By DNA-DNA hybridization, this new group exhibited <30% homology with recognized RGM species. The name Mycobacterium immunogenum sp. nov. is proposed for this new taxon.

Mycobacterium wolinskyi sp. nov. and Mycobacterium goodii sp. nov., two new rapidly growing species related to Mycobacterium smegmatis and associated with human wound infections: a cooperative study from the International Working Group on Mycobacterial Taxonomy.

Previous investigations demonstrated three taxonomic groups among 22 clinical isolates of Mycobacterium smegmatis. These studies were expanded to 71 clinical isolates, of which 35 (49%) (group 1) were identical to five ATCC reference strains including the type strain ATCC 19420T. Twenty-eight isolates (39%) were group 2, and eight isolates (11%) were group 3. Isolates of groups 2 and 3 were most often associated with post-traumatic or post-surgical wound infections including osteomyelitis, were susceptible to sulfamethoxazole, amikacin, imipenem and the tetracyclines, variably resistant to clarithromycin, and susceptible (group 1), intermediately resistant (group 2) or resistant (group 3) to tobramycin. The three groups were similar by routine biochemical and growth characteristics, but had different mycolic acid dimethoxy-4-coumarinylmethyl ester elution patterns by HPLC and different PCR-restriction enzyme patterns of a 439 bp fragment of the hsp-65 gene. Group 3 isolates differed from group 1 by 18 bp by 16S rRNA sequencing and exhibited < 25% homology by DNA-DNA hybridization, being most closely related to Mycobacterium mageritense. The 16S rRNA of group 1 and group 2 isolates differed by only 3 bp, but by DNA-DNA hybridization they exhibited only 40% homology. The following names are proposed: Mycobacterium goodii sp. nov. for group 2 isolates (type strain ATCC 700504T = MO69T), Mycobacterium wolinskyi sp. nov. for group 3 isolates (type strain ATCC 700010T = MO739T) and Mycobacterium smegmatis sensu stricto for group 1 isolates.

A single 16S ribosomal RNA substitution is responsible for resistance to amikacin and other 2-deoxystreptamine aminoglycosides in Mycobacterium abscessus and Mycobacterium chelonae.

Twenty-six clinical isolates of Mycobacterium abscessus resistant to amikacin were identified. Most isolates were from patients with posttympanostomy tube placement otitis media or patients with cystic fibrosis who had received aminoglycoside therapy. Isolates were highly resistant (MICs > 1024 microg/mL) to amikacin, kanamycin, gentamicin, tobramycin, and neomycin (all 2-deoxystreptamine aminoglycosides) but not to streptomycin. Sequencing of their 16S ribosomal (r) RNA revealed that 16 (94%) of 17 had an A-->G mutation at position 1408. In vitro-selected amikacin-resistant mutants of M. abscessus and Mycobacterium chelonae had the same resistance phenotype, and 15 mutants all had the same A-->G substitution at position 1408. Introducing an rRNA operon from Mycobacterium smegmatis with a mutated A-->G at this position into a single functional allelic rRNA mutant of M. smegmatis produced the same aminoglycoside resistance phenotype. These studies demonstrate this 16S rRNA mutation is responsible for amikacin resistance in M. abscessus, which has only one copy of the rRNA operon.

Genetic basis for clarithromycin resistance among isolates of Mycobacterium chelonae and Mycobacterium abscessus.

Resistance to clarithromycin among isolates of Mycobacterium chelonae and M. abscessus was observed in 18 of 800 (2.3%) patients tested between 1990 and 1995. Patients whose isolates were resistant had either disseminated disease or chronic lung disease, and the resistant isolates were recovered after clarithromycin monotherapy. Sequencing of the gene coding for the 23S rRNA peptidyltransferase region revealed a point mutation involving adenine at position 2058 (38%) or adenine at position 2059 (62%) in 20 of 20 relapse isolates from the first 13 patients identified. By pulsed-field gel electrophoresis or random amplified polymorphic DNA PCR, initial and relapse isolates were shown to have identical DNA patterns. M. chelonae and M. abscessus isolates were found to have only a single chromosomal copy of the rRNA operon, thus making them susceptible to single-step mutations. Thus, clarithromycin resistance in these species of rapidly growing mycobacteria relates to a point mutation in the gene coding for 23S rRNA and occurs in limited clinical situations, but was identified in almost 5% of isolates tested in 1995.

Initial clarithromycin monotherapy for Mycobacterium avium-intracellulare complex lung disease.

Sputum conversion rates in Mycobacterium avium-intracellulare (MAI) complex lung disease have ranged from only 50 to 80% despite the use of three to five antituberculosis agents. We initiated a prospective, open, noncomparative trial of initial clarithromycin monotherapy at 500 mg twice a day for 4 months in HIV-negative patients with MAI lung disease. The primary study end point was microbiologic improvement. Of 30 patients enrolled, 20 completed therapy. This latter group was predominantly male (60%), smokers (70%), older than 45 yr of age (90%), infected with Mycobacterium intracellulare (70%) and with bilateral disease (85%). Of 19 patients with pretreatment minimum inhibitory concentrations (MIC) for clarithromycin < 16 micrograms/ml, 58% became sputum-negative, and 21% showed significant reductions in sputum positivity. Heavily positive sputum cultures (> 200 colonies) were reduced from 30 to 47 samples pretherapy (64%) to three of 54 (6%) post-therapy (p < 0.0001); 18 of 19 patients (95%) showed an improvement in sputum cultures, chest radiographs, or both. Only two patients (7%) discontinued the drug because of adverse events. Only three (16%) of 19 isolates developed clarithromycin resistance (MIC > 32 micrograms/ml). Clarithromycin-susceptible and -resistant MAI isolates from the same patient had identical DNA large-restriction fragment patterns. Clarithromycin is the first single agent to be shown efficacious in the treatment of MAI lung disease.

Activities of clarithromycin against eight slowly growing species of nontuberculous mycobacteria, determined by using a broth microdilution MIC system.

MICs of clarithromycin against 324 clinical isolates belonging to eight species of slowly growing nontuberculous mycobacteria were determined by using a broth microdilution system. Isolates were inoculated into twofold drug dilutions in Middlebrook 7H9 broth (pH corrected to 7.4) and then incubated at 30 degrees C for 7 days for Mycobacterium marinum and for 14 days for all other species. The MIC for 90% of the strains (MIC90) was less than or equal to 0.5 micrograms/ml for isolates of Mycobacterium gordonae (6 strains), Mycobacterium scrofulaceum (5 strains), Mycobacterium szulgai (6 strains), and Mycobacterium kansasii (35 strains). MICs for M. marinum (25 strains) and Mycobacterium avium complex (237 strains) were higher, but 100% and 89% of the strains, respectively, were susceptible to less than or equal to 4 micrograms/ml. In contrast, MICs for five of six M. simiae strains were greater than 8 micrograms/ml, and the range of MICs for Mycobacterium nonchromogenicum varied from less than or equal to 0.125 to 8 micrograms/ml. For the 237 isolates of M. avium complex, the MIC50 was 2 micrograms/ml and the MIC90 was 8 micrograms/ml. MICs for most isolates (77%) were in the 1- to 4-micrograms/ml range. For the 80 isolates in this group known to be from AIDS patients, the MIC50 was 4 micrograms/ml and the MIC90 was 8 micrograms/ml. These MIC studies combined with preliminary clinical trials suggest that clarithromycin may be useful for drug therapy of most species of the slowly growing nontuberculous mycobacteria except M. simiae.

Skin, soft tissue, and bone infections due to Mycobacterium chelonae chelonae: importance of prior corticosteroid therapy, frequency of disseminated infections, and resistance to oral antimicrobials other than clarithromycin.

Little is known of clinical disease due to Mycobacterium chelonae chelonae. One hundred skin, soft tissue, or bone isolates of this rapidly growing mycobacterium were identified over 10 years. Clinical disease included disseminated cutaneous infection (53%); localized cellulitis, abscess, or osteomyelitis (35%); and catheter infections (12%). Underlying conditions with disseminated infection included organ transplantation, rheumatoid arthritis, and autoimmune disorders; 92% involved corticosteroid use. Trauma and medical procedures were risk factors for localized infections. Corticosteroids and chronic renal failure were risk factors for catheter infections. Overall, 62% of patients were receiving corticosteroids and 72% were immunosuppressed. MICs of six oral antimicrobials were obtained for 180 isolates by broth microdilution. Up to 20% of isolates were susceptible to doxycycline, ciprofloxacin, ofloxacin, and sulfamethoxazole. In contrast, 100% were susceptible to clarithromycin (MICs less than or equal to 1 microgram/mL). Disease due to M. chelonae chelonae usually occurs in the setting of corticosteroid therapy and is often disseminated; the organisms require high MICs of oral antimicrobials other than clarithromycin.

Activities of four macrolides, including clarithromycin, against Mycobacterium fortuitum, Mycobacterium chelonae, and M. chelonae-like organisms.

Susceptibilities to erythromycin by broth microdilution were compared with those to the newer macrolide clarithromycin for 223 isolates of rapidly growing mycobacteria belonging to seven taxonomic groups. Seventy-nine random isolates were also tested against azithromycin and roxithromycin. The MIC of clarithromycin for 90% of strains tested (MIC90) was 0.25 microgram/ml for isolates of Mycobacterium chelonae subsp. chelonae and 0.5 microgram/ml for M. chelonae subsp. abscessus, with 100% of strains inhibited by less than or equal to 1 microgram/ml. Clarithromycin was 10 to 50 times more active than erythromycin and four- to eightfold more active than the other newer macrolides against M. chelonae. MICs of clarithromycin frequently increased with prolonged incubation with isolates of M. chelonae subsp. abscessus but not M. chelonae subsp. chelonae. MICs of clarithromycin were much higher for M. fortuitum bv. fortuitum (MIC50, 2.0 microgram/ml; MIC90, greater than 8.0 microgram/ml). The three newer macrolides had comparable activity against M. fortuitum bv. peregrinum (MIC90s of 0.5 to 2.0 microgram/ml compared with erythromycin MIC90s of greater than 8.0 microgram/ml). Overall, clarithromycin was the most active agent, inhibiting all isolates of M. chelonae subsp. chelonae, M. chelonae subsp. abscessus, M. fortuitum bv. peregrinum, and the M. chelonae-like organisms and 35% of M. fortuitum bv. fortuitum at less than or equal to 1 microgram/ml. Clinical trials of the newer macrolides, especially clarithromycin, against these environmental mycobacterial species appear to be warranted.

Clinical and laboratory features of Nocardia nova.

Recent studies have shown that Nocardia asteroides isolates have five major antibiotic resistance patterns; one of these patterns identifies isolates of Nocardia farcinica. In the current study, we investigated a second pattern characterized by susceptibility to ampicillin and erythromycin. This pattern was seen in 17% of 223 clinical isolates identified by standard techniques as N. asteroides and associated with diseases typical for nocardiae. Biochemically, isolates with this drug pattern were relatively homogeneous and identical to the type strain and previous descriptions of Nocardia nova. The strains studied were unique among nocardiae in having both alpha- and beta-esterase activity (85 and 95%, respectively). However, the arylsulfatase activity at 14 days (75%) and antimicrobial susceptibility patterns, including susceptibility to erythromycin (100%), were the only routinely available methods that would separate N. nova strains from other members of N. asteroides. N. asteroides should be considered a complex because current clinical identification schemes include isolates of N. farcinica and N. nova and may well include additional species. This is the first detailed description of N. nova as a pathogen in humans.

Susceptibilities of Mycobacterium fortuitum biovar. fortuitum and the two subgroups of Mycobacterium chelonae to imipenem, cefmetazole, cefoxitin, and amoxicillin-clavulanic acid.

MICs of imipenem, cefoxitin, cefmetazole, and amoxicillin-clavulanic acid were determined against 100 strains of Mycobacterium fortuitum and 200 strains of Mycobacterium chelonae. Imipenem and cefmetazole were more active against M. fortuitum than cefoxitin was, and imipenem (which inhibited 39% of strains at 8 micrograms/ml) was the only beta-lactam active against M. chelonae subsp. chelonae.