Mycobacterium Avium Complex Clinical Isolates Research Articles

Biofilm Development by Mycobacterium avium Complex Clinical Isolates: Effect of Clarithromycin in Ultrastructure.

The Mycobacterium avium complex includes the commonest non-tuberculous mycobacteria associated with human infections. These infections have been associated with the production of biofilms in many cases, but there are only a few studies about biofilms produced by the species included in this group. Three collection strains (M. avium ATCC25291, M. intracellulare ATCC13950, and M. chimaera DSM756), three clinically significant strains (647, 657, and 655), and three clinically non-significant ones (717, 505, and 575) of each species were included. The clinical significance of the clinical isolates was established according to the internationally accepted criteria. The biofilm ultrastructure was studied by Confocal-Laser Scanning Microscopy by using BacLight Live-Dead and Nile Red stains. The viability, covered surface, height, and relative autofluorescence were measured in several images/strain. The effect of clarithromycin was studied by using the technique described by Muñoz-Egea et al. with modifications regarding incubation time. The study included clarithromycin in the culture medium at a concentration achievable in the lungs (11.3 mg/L), using one row of wells as the control without antibiotics. The bacterial viability inside the biofilm is expressed as a percentage of viable cells. The differences between the different parameters of the biofilm ultrastructure were analyzed by using the Kruskal-Wallis test. The correlation between bacterial viability in the biofilm and treatment time was evaluated by using Spearman's rank correlation coefficient (ρ). The strains showed differences between them with all the studied parameters, but neither a species-specific pattern nor a clinical-significance-specific pattern were detected. For the effect of clarithromycin, the viability of the bacteria contained in the biofilm was inversely proportional to the exposure time of the biofilm (ρ > -0.3; p-value < 0.05), excluding two M. chimaera strains (M. chimaera DSM756 and 575), which showed a weak positive correlation with treatment time (0.2 < ρ < 0.39; p-value < 0.05). Curiously, despite a clarithromycin treatment of 216 h, the percentage of the biofilm viability of the strains evaluated here was not less than 40% at best (M. avium 717). All the M. avium complex strains studied can form biofilm in vitro, but the ultrastructural characteristics between them suggest that these are strain-specific characteristics unrelated to the species or the clinical significance. The clarithromycin effect on MAC species is biofilm-age/time-of-treatment-dependent and appears to be strain-specific while being independent of the clinical significance of the strain.

Ceftriaxone Efficacy for Mycobacterium avium Complex Lung Disease in the Hollow Fiber and Translation to Sustained Sputum Culture Conversion in Patients.

Only 35.6%-50.8% of patients with Mycobacterium avium complex (MAC) pulmonary disease achieve sustained sputum culture conversion (SSCC) on treatment with the azithromycin-ethambutol-rifabutin standard of care (SOC). We tested the efficacy of ceftriaxone, a β-lactam with a lung-to-serum penetration ratio of 12.18-fold. We mimicked lung concentration-time profiles of 7 ceftriaxone once-daily doses for 28 days in the hollow fiber system model of intracellular MAC (HFS-MAC). Monte Carlo experiments were used for dose selection. We also compared once-daily ceftriaxone monotherapy to 3-drug SOC against 5 MAC clinical isolates in HFS-MAC using γ (kill) slopes, and translated to SSCC rates. Ceftriaxone killed 1.02-3.82 log10 colony-forming units (CFU)/mL, at optimal dose of 2 g once-daily. Ceftriaxone killed all 5 strains below day 0 versus 2 of 5 for SOC. The median γ (95% confidence interval [CI]) was 0.49 (.47-.52) log10 CFU/mL/day for ceftriaxone and 0.38 (.34-.43) log10 CFU/mL/day for SOC. In patients, the SOC was predicted to achieve SSCC rates (CI) of 39.3% (36%-42%) at 6 months. The SOC SSCC was 50% at 8.18 (3.64-27.66) months versus 3.58 (2.20-7.23) months for ceftriaxone, shortening time to SSCC 2.35-fold. Ceftriaxone is a promising agent for creation of short-course chemotherapy.

2135. Epetraborole in vitro Activity Against Mycobacterium avium complex Recent Clinical Isolates from Japan

Abstract Background Epetraborole (EBO) is a boron-containing, oral inhibitor of bacterial leucyl-tRNA synthetase, an essential enzyme in protein synthesis. EBO demonstrates potent activity against nontuberculous mycobacteria and is currently under clinical development for treatment of treatment-refractory Mycobacterium avium complex (MAC) lung disease. The objective of this study was to evaluate the in vitro activity of EBO against recent MAC isolates from Japan. Methods Minimal inhibitory concentration (MIC) values for EBO, amikacin (AMK), clarithromycin (CLR), rifabutin (RFB), and ethambutol (EMB) were determined using broth microdilution assays according to Clinical and Laboratory Standards Institute M24-A3 guideline (2018) against 110 MAC clinical isolates collected from Japanese patients in 2020. MAC isolates were of respiratory origin and included 55 M. avium and 55 M. intracellulare isolates. Results EBO (MIC) values ranged from 0.25 - 16 µg/mL and the EBO MIC50 and MIC90 were 2 and 4 µg/mL, respectively (Table 1). The CLR MIC range was 0.125 - &amp;gt; 32 µg/mL and included 4 CLR-resistant isolates (MIC ≥ 32 µg/mL). CLR MIC50 and MIC90 were 1 and 4 µg/mL, respectively. All isolates were susceptible to AMK and had an MIC range of 2 - 32 µg/mL; the MIC50 and MIC90 were 8 and 16 µg/mL, respectively. The EMB MIC range was 2 - &amp;gt; 32 µg/mL; the MIC50 and MIC90 were 4 and 16 µg/mL, and the RFB MIC range was ≤0.03 - 2 µg/mL and MIC50 and MIC90 were 0.06 and 0.25 µg/mL. EBO maintained activity with MIC values of 0.25 - 2 µg/mL against the 4 CLR-resistant isolates. Epetraborole and comparator antimicrobial minimum inhibitory concentration values against 110 recent Mycobacterium avium complex clinical isolates from Japan MIC=minimal inhibitory concentration; MIC50=minimal inhibitory concentration for 50% of isolates tested; MIC90=minimal inhibitory concentration for 90% of isolates tested. Conclusion EBO demonstrated potent in vitro activity against 110 recent MAC isolates collected from Japanese patients. Furthermore, EBO demonstrated in vitro activity against CLR-resistant MAC isolates suggesting that CLR-resistance does not impact EBO activity. These data are similar to results obtained against U.S. isolates and support the continued clinical evaluation of the use of EBO in the treatment of MAC lung disease in Japan. Disclosures Tiffany Keepers White, PhD, AN2 Therapeutics: Employee|AN2 Therapeutics: Stocks/Bonds Satoshi Mitarai, MD, PhD, AN2 Therapeutics, Inc.: Grant/Research Support

Phenotypic drug-susceptibility profiles and genetic analysis based on whole-genome sequencing of Mycobacterium avium complex isolates in Thailand.

Mycobacterium avium complex (MAC) infections are a significant clinical challenge. Determining drug-susceptibility profiles and the genetic basis of drug resistance is crucial for guiding effective treatment strategies. This study aimed to determine the drug-susceptibility profiles of MAC clinical isolates and to investigate the genetic basis conferring drug resistance using whole-genome sequencing (WGS) analysis. Drug-susceptibility profiles based on minimum inhibitory concentration (MIC) assays were determined for 38 MAC clinical isolates (12 Mycobacterium avium and 26 Mycobacterium intracellulare). Mutations associated with drug resistance were identified through genome analysis of these isolates, and their phylogenetic relationships were also examined. Drug resistance, based on MIC values, was most commonly observed for moxifloxacin (81.6%), followed by linezolid (78.9%), clarithromycin (44.7%) and amikacin (36.8%). We identified specific mutations associated with resistance to amikacin. These include the rrs mutation at C464T in amikacin intermediate-resistance M. avium, and two mutations at T250A and G1453T in amikacin non-susceptible M. intracellulare. Mutations in rrl at A2058G, A2059C and A2059G were potentially linked to clarithromycin resistance. MAC clinical isolates not susceptible to linezolid exhibited mutations in rplC at G237C and C459T, as well as two rplD mutations at G443A and A489G. GyrB substitution Thr521Ala (T521A) was identified in moxifloxacin non-susceptible isolates, which may contribute to this resistance. A phylogeny of our MAC isolates revealed high levels of genetic diversity. Our findings suggest that the standard treatment regimen for MAC infections using moxifloxacin, linezolid, clarithromycin and amikacin may be driving development of resistance, potentially due to specific mutations. The combination of phenotypic and genotypic susceptibility testing can be valuable in guiding the clinical use of drugs for the treatment of MAC infections.

Evaluating amikacin minimum inhibitory concentration in trailing growth for Mycobacterium avium complex

BackgroundAmikacin is a first-line drug that must be evaluated when performing an antimycobacterial susceptibility test (AST) for Mycobacterium avium complex (MAC). However, the presence of sporadic trailing growth in MAC makes determining the precise point for reading its minimal inhibitory concentration (MIC) challenging. MethodsSusceptibility was re-tested for 134 MAC clinical isolates using the Sensititre SLOMYCOI panel, the rrs gene was sequenced, and amikacin exposure history was investigated. The MIC50, MIC90, and the epidemiological cut-off value (ECOFF) were calculated using the EUCAST method. ResultsAfter re-testing and ignoring trailing growth, of the 22 M. intracellulare isolates originally classified as resistant to amikacin according to the CLSI guideline, 10 strains were reclassified as intermediate and four as susceptible. Similarly, from the seven resistant M. avium strains, one was reclassified as intermediate and four as susceptible. No rrs gene mutations were detected in any isolates, including resistant strains. When ignoring trailing growth, the calculated MIC50, MIC90, and ECOFF values closely aligned with the EUCAST MIC distribution. ConclusionTo maintain the current CLSI breakpoint, trailing growth should be ignored when reading the amikacin MIC of MAC. To read the MIC at complete bacterial inhibition, the CLSI breakpoint needs to be raised.

In Vitro Effect of Three-Antibiotic Combinations plus Potential Antibiofilm Agents against Biofilm-Producing Mycobacterium avium and Mycobacterium intracellulare Clinical Isolates.

Patients with chronic pulmonary diseases infected by Mycobacterium avium complex (MAC) often develop complications and suffer from treatment failure due to biofilm formation. There is a lack of correlation between in vitro susceptibility tests and the treatment of clinical isolates producing biofilm. We performed susceptibility tests of 10 different three-drug combinations, including two recommended in the guidelines, in biofilm forms of eight MAC clinical isolates. Biofilm developed in the eight isolates following incubation of the inoculum for 3 weeks. Then, the biofilm was treated with three-drug combinations with and without the addition of potential antibiofilm agents (PAAs). Biofilm bactericidal concentrations (BBCs) were determined using the Vizion lector system. All selected drug combinations showed synergistic activity, reducing BBC values compared to those treated with single drugs, but BBC values remained high enough to treat patients. However, with the addition of PAAs, the BBCs steadily decreased, achieving similar values to the combinations in planktonic forms and showing synergistic activity in all the combinations and in both species. In conclusion, three-drug combinations with PAAs showed synergistic activity in biofilm forms of MAC isolates. Our results suggest the need for clinical studies introducing PAAs combined with antibiotics for the treatment of patients with pulmonary diseases infected by MAC.

In vitro and intracellular activities of novel thiopeptide derivatives against macrolide-susceptible and macrolide-resistant Mycobacterium avium complex.

Unsatisfactory outcomes following long-term multidrug treatment in patients with Mycobacterium avium complex (MAC) pulmonary disease have urged us to develop novel antibiotics. Thiopeptides, a class of peptide antibiotics derived from natural products, have potential as drug candidates that target bacterial ribosomes, but drug development has been hampered due to their extremely poor solubility. Here, we evaluated three new compounds (AJ-037, AJ-039, and AJ-206) derived from the thiopeptide micrococcin P2 with enhanced aqueous solubility; the derivatives were generated based on structure-activity relationship analysis. We conducted in vitro drug susceptibility and intracellular antimycobacterial activity testing of the three thiopeptide derivatives against various MAC strains, including macrolide-resistant MAC clinical isolates. These compounds showed low MICs against MAC, similar to that of clarithromycin (CLR). In particular, two compounds, AJ-037 and AJ-206, had intracellular antimycobacterial activities, along with synergistic effects with CLR, and inhibited the growth of MAC inside macrophages. Moreover, these two compounds showed in vitro and intracellular anti-MAC activities against macrolide-resistant MAC strains without showing cross-resistance with CLR. Taken together, the results of the current study suggest that AJ-037 and AJ-206 can be promising anti-MAC agents for the treatment of MAC infection, including for macrolide-resistant MAC strains. IMPORTANCE Novel antibiotics for the treatment of MAC infection are urgently needed because the treatment outcomes using the standard regimen for Mycobacterium avium complex (MAC) pulmonary disease remain unsatisfactory. Here, we evaluated three novel thiopeptide derivatives (AJ-037, AJ-039, and AJ-206) derived from the thiopeptide micrococcin P2, and they were confirmed to be effective against macrolide-susceptible and macrolide-resistant MAC. Our thiopeptide derivatives have enhanced aqueous solubility through structural modifications of poorly soluble thiopeptides. The thiopeptide derivatives showed minimal inhibitory concentrations against MAC that were comparable to clarithromycin (CLR). Notably, two compounds, AJ-037 and AJ-206, exhibited intracellular antimycobacterial activities and acted synergistically with CLR to hinder the growth of MAC within macrophages. Additionally, these compounds demonstrated in vitro and intracellular anti-MAC activities against macrolide-resistant MAC strains without showing any cross-resistance with CLR. We believe that AJ-037 and AJ-206 can be promising anti-MAC agents for the treatment of MAC infections, including macrolide-resistant MAC strains.

Identification and drug susceptibility testing of the subspecies of Mycobacterium avium complex clinical isolates in mainland China

ObjectivesThe Mycobacterium avium complex (MAC), comprising a series of subspecies, has a worldwide distribution, with differences in drug susceptibility among subspecies. This study aimed to assess the composition of MAC and susceptibility differences among subspecies in mainland China. MethodsA total of 287 MAC clinical strains were included in the study. Multitarget sequences were applied to accurately identify subspecies, and a microdilution method was used to evaluate minimum inhibitory concentrations (MICs) among subspecies using Sensititre SLOMYCO plates. ResultsMycobacterium intracellular (N = 169), Mycobacterium avium (N = 52), Mycobacterium chimaera (N = 22), Mycobacterium marseillense (N = 25), Mycobacterium colombiense (N = 14), Mycobacterium yongonense (N = 4), Mycobacterium vulneris (N = 3) and Mycobacterium timonense (N = 2) were isolated from MAC. Clarithromycin, amikacin and rifabutin showed lower MIC50 and MIC90 values than other drugs, and the resistance rates of clarithromycin, amikacin, linezolid and moxifloxacin were 6.3%, 10.5%, 51.9% and 46.3%, respectively. The resistance rates of clarithromycin and moxifloxacin in the initial treatment group were significantly lower than those in the retreatment group (4.09% vs. 12.94%; 30.41% vs. 75.29%; P < 0.05). Drug susceptibility differences were observed in clarithromycin and moxifloxacin among the five major subspecies (P < 0.05); however, those statistically significant differences disappeared when MACs were divided into two groups according to previous anti-tuberculosis (anti-TB) treatment history. ConclusionThis study revealed that MAC, primarily comprising M. intracellulare, was susceptible to clarithromycin, amikacin and rifabutin. Drug susceptibility among subspecies did not exhibit intrinsic differences in our study. Previous anti-TB treatment patients are more resistant to drugs; thus, attention should be given to those patients in the clinic.

Effect of efflux pump inhibitors on the susceptibility of Mycobacterium avium complex to clarithromycin.

In this study we aimed to evaluate the effect of the combination of clarithromycin and four inhibitors of efflux pumps (EPIs), including berberine (BER), carbonyl cyanide m-chlorophenylhydrazone (CCCP), piperine (PIP) and tetrandrine (TET), against 12 Mycobacterium avium complex clinical isolates. The minimum inhibitory concentration (MIC) of clarithromycin showed at least a fourfold reduction in presence of BER (83% of total isolates), CCCP (67%), PIP (25%) and TET (75%). Our results showed that the EPIs tested are active against both clarithromycin susceptible and resistant isolates. In particular, among the six resistant isolates, TET reversed the resistance phenotype of three strains, BER of two strains, and CCCP and PIP of one strain. Overall, our findings show the importance of these compounds in increasing the efficacy of clarithromycin in MAC clinical isolates.

Minocycline treatment for pulmonary Mycobacterium avium complex disease based on pharmacokinetics/pharmacodynamics and Bayesian framework mathematical models.

Our aim was to identify the pharmacokinetic/pharmacodynamic parameters of minocycline in the hollow-fibre system (HFS) model of pulmonary Mycobacterium avium complex (MAC) and to identify the optimal clinical dose. Minocycline MICs for 55 MAC clinical isolates from the Netherlands were determined. We also co-incubated primary isolated macrophages infected with MAC with minocycline. Next, we performed a 28 day HFS-MAC model dose-response study in which we mimicked pulmonary concentration-time profiles achieved in patients. The HFS-MAC model was sampled at intervals to determine the minocycline pharmacokinetics and MAC burden. We identified the AUC0-24/MIC ratios associated with 1.0 log10 cfu/mL kill below day 0 (stasis), defined as a bactericidal effect. We then performed 10000 Monte Carlo experiments to identify the optimal dose for a bactericidal effect in patients. The MIC for 50% and 90% of cumulative clinical isolates was 8 and 64 mg/L, respectively. Minocycline decreased MAC bacterial burden below stasis in primary isolated macrophages. In the HFS-MAC model, minocycline achieved a microbial kill of 3.6 log10 cfu/mL below stasis. The AUC0-24/MIC exposure associated with a bactericidal effect was 59. Monte Carlo experiments identified a minocycline susceptibility MIC breakpoint of 16 mg/L. At this proposed breakpoint, the clinical dose of 200 mg/day achieved the bactericidal effect exposure target in ∼50% of patients, while 400 mg/day achieved this in 73.6% of patients, in Monte Carlo experiments. Minocycline at a dose of 400 mg/day is expected to be bactericidal. We propose a clinical trial for validation.

Design, synthesis and activity of thio-linked arabinofuranosyl disaccharides against mycobacterial tuberculosis (MTB) and Mycobacterium avium complex (MAC)

We report the chemical synthesis of a series of disaccharides of arabinofuranose with a glycosidic sulfur linker as mimics of the acceptor for arabinofuranosyltransferases with and without using any activator to avoid any complex reactions. These analogs were tested for in vitro activity against MTB strain H37Ra and 3 MAC clinical isolates. MICs were determined using a colorimetric microdilution broth assay. Bactericidal activity was studied with kill curves over a period of seven days. Intracellular activity against MTB H37Ra was determined in the Mono Mac 6 (MM6) human monocytic cell line.

Determination of ansamycin MICs for Mycobacterium avium complex in liquid medium by radiometric and conventional methods.

A radiometric method to determine the MIC of ansamycin (LM427) for Mycobacterium avium complex clinical isolates has been developed. It is based on a comparison of the conventional growth curve determination and the radiometric detection of growth (growth index) in the same liquid medium (7H12 broth). This new method requires less time and labor than does a conventional determination of MIC in liquid medium (CFU). Other advantages of this method include relatively short periods of exposure of the drug to 37 degrees C and the composition of 7H12 broth, which has practically no substrates which could absorb or bind the drug. Thus, a more accurate estimation of the MIC in this medium can be expected than by the conventional agar dilution (proportion) method. The MICs of ansamycin appeared to be higher in agar plates than in 7H12 broth. More than 70% of the isolates had a broth-determined MIC one to three times lower than the average peak concentration of ansamycin achieved in sera of patients. The wide range of MICs suggests the importance of testing susceptibility in broth with many concentrations in addition to, or rather than in, agar plates with concentrations of 2.0 or 1.0 micrograms/ml only. Taking into account relatively low levels of ansamycin in sera of patients, it would be appropriate to compare the MICs with the levels in serum to make the outcome of chemotherapy more predictable.