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.     

In vitro activities of the novel oxazolidinones DA-7867 and DA-7157 against rapidly and slowly growing mycobacteria

DA-7867 and DA-7157 are oxazolidinones active against pathogenic aerobic actinomycetes including Nocardia spp. and Mycobacterium tuberculosis. However, the activity of these drugs against nontuberculous mycobacterium (NTM) species is not known. In this work, we compared the susceptibilities of 122 clinical isolates and 29 reference species of both rapidly growing and slowly growing mycobacteria to linezolid, DA-7867, and DA-7157 by the broth microdilution method. The MICs for 50 and 90% of the strains tested (MIC50s and MIC90s, respectively) of DA-7867 and DA-7157 were lower than those of linezolid. In all of the cases, a MIC90 of <8 microg/ml was observed for all of the species tested in both groups of NTM. For M. kansasii and M. marinum isolates, the MIC90s of both DA-7867 and DA-7157 were less than 0.5 microg/ml. These results demonstrate the potential of these compounds to treat NTM infections.     

In vitro activity of linezolid against slowly growing nontuberculous Mycobacteria

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 相似文献   

Antibiotic susceptibility pattern of Mycobacterium marinum

In vitro activities of 17 antibiotics against 53 clinical strains of Mycobacterium marinum, an atypical mycobacterium responsible for cutaneous infections, were determined using the reference agar dilution method. Rifampin and rifabutin were the most active drugs (MICs at which 90% of the isolates tested were inhibited [MIC(90)s], 0.5 and 0.6 microgram/ml, respectively). MICs of minocycline (MIC(90), 4 microgram/ml), doxycycline (MIC(90), 16 microgram/ml), clarithromycin (MIC(90), 4 microgram/ml), sparfloxacin (MIC(90), 2 microgram/ml), moxifloxacin (MIC(90), 1 microgram/ml), imipenem (MIC(90), 8 microgram/ml), sulfamethoxazole (MIC(90), 8 microgram/ml) and amikacin (MIC(90), 4 microgram/ml) were close to the susceptibility breakpoints. MICs of isoniazid, ethambutol, trimethoprim, azithromycin, ciprofloxacin, ofloxacin, and levofloxacin were above the concentrations usually obtained in vivo. For each drug, the MIC(50), geometric mean MIC, and modal MIC were very close, showing that all the strains had a similar susceptibility pattern. Percent agreement (within +/-1 log(2) dilution) between MICs yielded by the Etest method and by the agar dilution method used as reference were 83, 59, 43, and 24% for minocycline, rifampin, clarithromycin, and sparfloxacin, respectively. Reproducibility with the Etest was low, in contrast to that with the agar dilution method. In conclusion, M. marinum is a naturally multidrug-resistant species for which the agar dilution method is more accurate than the Etest for antibiotic susceptibility testing.     

In vitro activities of free and liposomal drugs against Mycobacterium avium-M. intracellulare complex and M. tuberculosis.

We compared MICs and MBCs of various free- and liposome-incorporated antimicrobial agents against several patient isolates of Mycobacterium avium-M. intracellulare complex and certain American Type Culture Collection strains of M. avium, M. intracellulare, and Mycobacterium tuberculosis. Seven of 19 agents were selected for incorporation into liposomes. The MICs of these agents for 50 and 90% of isolates tested (MIC50s and MIC90s, respectively) ranged from 0.5 to 62 micrograms/ml. Members of the M. avium-M. intracellulare complex were resistant to killing by most of the other agents tested in the free form. However, clofazimine, resorcinomycin A, and PD 117558 showed complete killing of bacteria at concentrations ranging from 8 to 31 micrograms/ml, represented as MBC90s. Among the liposome-incorporated agents, clofazimine and resorcinomycin A had the highest killing effects (MBC90s, 8 and 16 micrograms/ml, respectively). Furthermore, both free and liposome-incorporated clofazimine had equivalent growth-inhibitory and killing effects on all American Type Culture Collection strains of M. avium, M. intracellulare, and M. tuberculosis tested. These results show that the antibacterial activities of certain drugs, particularly those of clofazimine and resorcinomycin, were maintained after the drugs were incorporated into liposomes.     

Effect of pH on the in vitro potency of clarithromycin against Mycobacterium avium complex.

Employing 7H11 agar medium at pH 6.6, the MICs of clarithromycin for 50% (MIC50) and 90% (MIC90) of 19 strains of Mycobacterium avium complex were 8 and 16 micrograms/ml, respectively. However, the MICs were 2 to 3 log2 dilutions lower in the 7H11 medium adjusted to pH 7.4, and the MICs on 10% OADC (oleic acid-albumin-dextrose-catalase)-enriched Mueller-Hinton agar at pH 7.3 were also 2 log2 dilutions lower than those measured on 7H11 agar at pH 6.6. Therefore, clarithromycin is more active at a physiologic than at an acidic pH.     

Activities of sparfloxacin, azithromycin, temafloxacin, and rifapentine compared with that of clarithromycin against multiplication of Mycobacterium avium complex within human macrophages.

The activities of sparfloxacin, azithromycin, temafloxacin, and rifapentine against two virulent strains of the Mycobacterium avium complex isolated from patients with AIDS were evaluated in a model of intracellular infection and were compared with that of clarithromycin. Human monocyte-derived macrophages were infected with the M. avium complex at day 6 of culture. The intracellular CFU was counted 60 min after inoculation. The intracellular and supernatant CFU was counted on days 4 and 7 after inoculation. The concentrations used, which were equal to peak levels in serum, were 10 micrograms of rifapentine per ml (MICs for the two strains, 4 and 16 micrograms/ml), 4 micrograms of clarithromycin per ml (MICs, 8 and 4 micrograms/ml), 1 microgram of azithromycin per ml (MICs, 32 and 16 micrograms/ml), 4 micrograms of temafloxacin per ml (MICs, 2 and 16 micrograms/ml), and 1 microgram of sparfloxacin per ml (MICs, 0.5 and 2 micrograms/ml). Compared with controls on day 7 after inoculation, clarithromycin (P less than 0.001), sparfloxacin (P less than 0.001), and azithromycin (P less than 0.001 for the first strain, P less than 0.02 for the second) slowed intracellular replication. Rifapentine (P less than 0.001) and temafloxacin (P less than 0.001) slowed intracellular replication of the first strain but not of the second strain. Azithromycin plus sparfloxacin was as effective as sparfloxacin alone. In this macrophage model, sparfloxacin or clarithromycin (difference not significant) exhibited a better efficacy than rifapentine, azithromycin, or temafloxacin against intracellular M. avium complex infection.     

In vitro susceptibilities of rapidly growing mycobacteria to newer antimicrobial agents.

The in vitro antimicrobial susceptibilities of 42 isolates of rapidly growing mycobacteria (Mycobacterium fortuitum, M. chelonae, and Mycobacterium species [other than M. fortuitum and M. chelonae]) to nine quinolones, including newer agents, two new aminoglycosides, and an aminocyclitol (trospectomycin) were determined by a broth microdilution method. The new quinolones, PD 117596, PD 127391, and PD 117558, showed excellent in vitro activities against M. fortuitum (MICs for 90% of isolates [MIC90s], 0.06, 0.06, and 0.12 microgram/ml, respectively). The MIC90 of ciprofloxacin for M. fortuitum was 0.5 microgram/ml. Only 14 to 28% of isolates of M. chelonae were susceptible to various quinolones. Most isolates of all three species were susceptible to the new aminoglycosides SCH 21420 and SCH 22591. The MIC90s of trospectomycin were 8 micrograms/ml for M. chelonae, 32 micrograms/ml for Mycobacterium species, and > 64 micrograms/ml for M. fortuitum.     

Isolation and characterizations of clarithromycin-resistant Mycobacterium avium clinical isolates

Mycobacterium avium is an important intracellular pathogen, particularly in AIDS patients. It also shows the second frequency among nontuberculous mycobacteria infections in Korea. Point mutations of domain V region of the 23S rRNA gene has been known to confer clarithromycin resistance to M. avium. In order to isolate the clarithromycin-resistant strains from clinical isolates of M. avium and characterize them, we isolated the clarithromycin-resistant strains from clinical isolates of M. avium using reverse hybridization assay (RHA) and broth microdilution test (BMT). Three clarithromycin-resistant isolates with high level of MICs were found from 274 clinical isolates by BMT. Two of three resistant strains were also found by RHA, which revealed point mutations in the domain V region of the 23S rRNA. We report here clarithromycin-resistant clinical isolates of M. avium with the different characteristics from those of the resistant strains reported from earlier studies.     

Comparative in vitro activities of ampicillin, BMY 28142, and imipenem against Mycobacterium avium complex

The in vitro activity of ampicillin, BMY 28142, and imipenem was evaluated against 21 clinical isolates of Mycobacterium avium complex by both a broth and an agar dilution method. The MIC90 by broth dilution for ampicillin, BMY 28142, and imipenem was 16 micrograms/ml, 8 micrograms/ml, and greater than 32 micrograms/ml, respectively. The MIC90 by agar dilution for ampicillin and BMY 28142 was 16 micrograms/ml.     

In vitro activities of sparfloxacin, tosufloxacin, ciprofloxacin, and fleroxacin.

The in vitro activity of sparfloxacin was compared with those of tosufloxacin, ciprofloxacin, and fleroxacin against 730 bacterial isolates representing 49 different species. Sparfloxacin and ciprofloxacin had similar spectra of activity, but sparfloxacin was less active against Pseudomonas aeruginosa and more active against many gram-positive cocci and anaerobic bacteria. Tosufloxacin MICs were generally 8- to 16-fold lower than those for sparfloxacin or ciprofloxacin. All four fluoroquinolones were active against nalidixic acid-susceptible strains of the family Enterobacteriaceae (MIC for 90% of the isolates [MIC90], less than or equal to 0.25 micrograms/ml) but nalidixic acid-resistant strains were less susceptible (MIC90, greater than or equal to 4.0 micrograms/ml). Against Pseudomonas aeruginosa isolates, MIC90s were 1.0 micrograms/ml for tosufloxacin, 2.0 micrograms/ml for ciprofloxacin, and 4.0 micrograms/ml for sparfloxacin. Against Enterococcus faecalis, sparfloxacin and ciprofloxacin MIC90s were 1.0 and 2.0 micrograms/ml, respectively. MIC90s for ciprofloxacin-susceptible Staphylococcus aureus were 0.016 micrograms/ml for tosufloxacin, 0.06 micrograms/ml for sparfloxacin, and 0.5 micrograms/ml for both ciprofloxacin and fleroxacin. With four species of gram-negative bacilli, mutants resistant to two to four times the sparfloxacin MIC occurred spontaneously at frequencies of 10(-7) to 10(-9): single-step high-level resistance was not observed. In vitro-selected sparfloxacin-resistant mutants displayed cross-resistance to other quinolones, as did clinical isolates of ciprofloxacin-resistant S. aureus. Tosufloxacin MICs with broth microdilution methods were four- to eightfold greater than those obtained with agar dilution methods. The two procedures gave comparable results when sparfloxacin or ciprofloxacin was being tested.     

In vitro susceptibility of Mycobacterium kansasii to clarithromycin.

The MICs of the macrolide clarithromycin for 31 clinical isolates of Mycobacterium kansasii were determined by three different methods. The methods employed were the proportion resistance method on 7H10 agar, the radiometric (BACTEC) method, and the T100 method of datum analysis. All methods gave similar results. The MICs were in a narrow range from 0.16 to 0.50 microgram/ml, with the MICs for 90% of isolates tested of 0.50 microgram/ml for the agar dilution and radiometric methods and 0.37 microgram/ml for the T100 method. The MBCs were determined for nine representative isolates by the radiometric broth method. The MBCs were equal to the MICs for four isolates, and the MBCs were twofold higher than the MICs for five isolates. Killing of 99.9% of the bacterial population was achieved at a clarithromycin concentration of 2.0 micrograms/ml for all nine isolates tested.     

Activities of ciprofloxacin and ofloxacin against rapidly growing mycobacteria with demonstration of acquired resistance following single-drug therapy.

The susceptibility to ciprofloxacin of 548 clinical isolates of rapidly growing mycobacteria belonging to eight subgroups or species was determined. The 170 isolates of Mycobacterium fortuitum biovar.fortuitum were most susceptible; the MIC for 90% of the organisms was 0.125 micrograms/ml. The other biovariants of M. fortuitum, M. smegmatis, and the M. chelonae-like organisms were less susceptible; the modal MIC was 0.5 micrograms/ml, and the MIC for 90% of organisms was 1.0 micrograms/ml. The two subspecies of M. chelonae were generally resistant, with only 8% of 206 isolates falling in the moderately susceptible category (MIC, 2 micrograms/ml) and only 2% falling in the susceptible category (MIC, less than or equal to 1 micrograms/ml). MICs of ofloxacin averaged 1 to 2 dilutions higher than those of ciprofloxacin for all subgroups tested. Three patients with M. fortuitum cutaneous disease relapsed after an initial response to therapy with ciprofloxacin, and their isolate was shown to have acquired drug resistance. Mutational frequencies for M. fortuitum with ciprofloxacin were relatively high (10(-5) to 10(-7), and MICs for single-step mutants were similar to those for the clinically resistant strains. Thus, despite the excellent activity of ciprofloxacin against rapidly growing mycobacterial groups other than M. chelonae, single-drug therapy should be used with caution because of the risk of development of mutational resistance.     

In vitro activity of decaplanin (M86-1410), a new glycopeptide antibiotic.

The in vitro activity of decaplanin (formerly M86-1410), a novel glycopeptide antimicrobial agent, was tested against 169 gram-positive bloodstream isolates from patients at the University of Iowa Hospitals and Clinics and 12 selected vancomycin-resistant strains. Enterococcus faecalis, E. faecium, Staphylococcus aureus, streptococci, bacilli, corynebacteria, and listeria were inhibited by decaplanin (MICs for 90% of the strains tested [MIC90s], 0.12 to 4 micrograms/ml). However, some rarely isolated and selected Enterococcus sp. populations had a MIC90 of 16 micrograms/ml, and S. haemolyticus strains had a MIC90 of 8 micrograms/ml. These in vitro results suggest that decaplanin may be useful against most gram-positive strains, even though some Enterococcus species and coagulase-negative staphylococci were potentially resistant (MICs, greater than or equal to 8 micrograms/ml).     

Characterization of resistance phenotype and cephalosporin activity in oxacillin-resistant Staphylococcus aureus

Forty isolates of methicillin-resistant Staphylococcus aureus were tested versus oxacillin at 30 and 35 degrees C with and without 2% NaCl supplementation of Mueller-Hinton broth and classified as having resistance that was low (MIC, less than or equal to 16 micrograms/ml) or high (MIC, greater than or equal to 32 micrograms/ml) and temperature or NaCl dependent. Only three isolates had low-grade resistance at both 30 and 35 degrees C; for two isolates the MICs at 35 degrees C were greater than or equal to 4 X the MICs at 30 degrees C. NaCl usually increased the MICs two- to fourfold. Efficiency of plating studies were performed on strains selected for their level of oxacillin resistance and according to temperature-related difference in MICs. Most strains appeared to represent the heterogeneous resistance phenotype. Cefamandole MICs were little affected by temperature but increased with NaCl. With three exceptions, cefamandole MCBs were less than or equal to 4 X MICs. For only six isolates were cefuroxime MICs less than or equal to 16 micrograms/ml. Four strains that were susceptible to both cefuroxime and cefamandole were selected for time-killing curve studies at inocula of 10(7) CFU/ml. At 8 X MIC, cefuroxime failed to reduce the concentration of any strain by greater than or equal to 3 X log10 CFU/ml. Killing of greater than or equal to 3 X log10 CFU/ml was achieved by cefamandole at 4X and 8 X MIC in one strain, at 8 X MIC only in two strains, and by neither 4 X nor 8 X MIC in one strain. Within therapeutically attainable blood levels, cefuroxime is essentially inactive and cefamandole is variably bactericidal against oxacillin-resistant s. aureus.     

In vitro and in vivo activities of clarithromycin against Mycobacterium avium.

There is no effective therapy to treat Mycobacterium avium complex infection in patients with acquired immune deficiency syndrome. Clarithromycin (A-56268; TE-031) is a new macrolide which is twofold more active than erythromycin against most aerobic bacteria. In addition, higher levels in serum and tissue are achieved with clarithromycin than with erythromycin. In this study, clarithromycin, erythromycin, difloxacin, temafloxacin, ciprofloxacin, rifampin, amikacin, and ethambutol were tested in vitro and in vivo against the M. avium complex. The MICs for 90% of strains tested were 4 micrograms/ml for clarithromycin, 64 micrograms/ml for erythromycin, 32 micrograms/ml for difloxacin, 8 micrograms/ml for temafloxacin, 4 micrograms/ml for ciprofloxacin, 4 micrograms/ml for rifampin, 32 micrograms/ml for amikacin, and 32 micrograms/ml for ethambutol. Beige mice were infected intravenously with 10(7) CFU of M. avium ATCC 25291. Treatment was started on day 6 after infection and was administered twice a day at 8-h intervals for 9 days. Clarithromycin was the most effective compound in these tests and was effective in reducing the viable bacterial counts in the spleen when it was administered subcutaneously or orally at a dose of 25 mg/kg. Amikacin was the only other compound which showed activity in vivo. The peak concentration in serum at which clarithromycin was active was approximately 1.0 microgram/ml.     

Effect of calcium on in vitro activity of LY146032 against Clostridium difficile.

The in vitro MICs of LY146032 against 63 isolates of Clostridium difficile tested in Wilkins-Chalgren broth ranged from 0.5 to greater than 32 micrograms/ml, with MICs of 4 and 8 micrograms/ml for 50 and 90% of the isolates, respectively. However, when the test medium was supplemented with physiologic concentrations of calcium, the MIC for 90% of the isolates was reduced to less than or equal to 0.12 microgram/ml.     

In vitro evaluation of HR810, a new wide-spectrum aminothiazolyl alpha-methoxyimino cephalosporin

HR810 (Hoechst-Roussel Pharmaceuticals Inc., Somerville, N.J.) is a new, cyclical-pyridinium cephalosporin that appeared superior to numerous comparison drugs against 658 strains of aerobic and facultative anaerobic bacteria. Seventeen Enterobacteriaceae spp. were tested by broth microdilution methods, and the 50% MICs (MIC50S) and 90% MICs (MIC90s) were 0.03 to 0.12 and 0.03 to 2.0 micrograms/ml, respectively. Only one strain had an MIC greater than 8.0 micrograms/ml (99.6% is considered susceptible). HR810 inhibited 98% of Pseudomonas aeruginosa isolates at less than or equal to 16 micrograms/ml, and the MIC90 for Acinetobacter spp. was 4.0 micrograms/ml. It was also very active against Pseudomonas spp. and Staphylococcus aureus (MIC90, 0.5 micrograms/ml) but marginally active against methicillin-resistant staphylococcal strains (MIC90, 16 micrograms/ml) and enterococcus (MIC90, 32 micrograms/ml). Non-enterococcal streptococci had MIC50s ranging from 0.008 micrograms/ml for Streptococcus pyogenes to 0.12 micrograms/ml for pneumococci. All MICs of HR810 against Haemophilus and Neisseria spp. were less than or equal to 0.03 micrograms/ml (MIC50, 0.002 to 0.008 micrograms/ml). HR810 poorly inhibited beta-lactamases and was very stable against 11 tested beta-lactamases of plasmid (TEM, OXA, SHV-1, and PSE) and chromosomal (K1, K14, P99) types.     

Enhanced in vitro activity of WR99210 in combination with dapsone against Mycobacterium avium complex.

WR99210, a dihydrofolate reductase inhibitor, has promising in vitro activity against Mycobacterium avium complex (MAC). The in vitro activities of WR99210 alone and in combination with a fixed concentration of dapsone (0.5 microgram/ml) were evaluated against 35 clinical MAC isolates by a broth dilution method. The MIC at which 50% of isolates were inhibited (MIC50) and MIC90 of WR99210 alone were 2 and 8 micrograms/ml, respectively. The MIC50 and MIC90 of WR99210 in combination with dapsone were 0.25 and 4 micrograms/ml, respectively. Overall, 75% of the MAC isolates displayed enhanced susceptibility to the combination.     

Activities of antimicrobial agents against clinical isolates of Mycobacterium haemophilum.

Mycobacterium haemophilum, first described in 1978, can cause severe infections of skin, respiratory tract, bone, and other organs of immunocompromised patients. There is no standardized antimicrobial susceptibility test, and for the 27 reported cases, a variety of test methods have been used. This paper reports the in vitro test results for 17 isolates of M. haemophilum recovered from 12 patients in the New York City area. MICs of 16 antimicrobial agents were determined in microtiter trays containing Middlebrook 7H9 broth plus 60 microM hemin, inoculated with 10(6) CFU of the organism per ml and incubated at 30 degrees C for 10 days. Ethambutol, ethionamide, tetracycline, cefoxitin, and trimethoprim-sulfamethoxazole were inactive against initial isolates from the 12 patients. Isoniazid was weakly active with a MIC for 50% of strains tested (MIC50) of 8 micrograms/ml and a MIC90 of > 32 micrograms/ml. Three quinolones, ciprofloxacin, ofloxacin, and sparfloxacin, were moderately active with MIC50s of 2 to 4 micrograms/ml and MIC90s of 4 to 8 micrograms/ml. Amikacin and clofazamine were active with MIC90s of 4 and 2 micrograms/ml, respectively. Clarithromycin was the most active macrolide with a MIC90 of < or = 0.25 microgram/ml. The MIC90 of azithromycin was 8 micrograms/ml, and the MIC90 of erythromycin was 4 micrograms/ml. The rifamycins were active with a MIC90 of 1 microgram/ml for rifampin and one of < or = 0.03 micrograms/ml for rifabutin. For a second isolate from the skin of one patient and a isolate from an autopsy culture of the spleen of a second patient, MICs of rifampin and rifabutin were > 16 microgram/ml, whereas initial isolates were inactivated by low concentrations of the rifamycins. Both patients had been treated for several months with several antimicrobial agents, including a rifamycin.