In Vitro MIC Values of Rifampin and Ethambutol and Treatment Outcome in Mycobacterium avium Complex Lung Disease

In vitro susceptibility patterns for slowly growing non-tuberculous mycobacteria in the USA from 2018 to 2022

BACKGROUND

Treatment of slowly growing non-tuberculous mycobacteria (SGM) is challenging. In vitro antimicrobial susceptibility testing (AST) is needed to optimize a multidrug regimen but requires weeks to result. Aggregated AST patterns, or an antibiogram, of SGM would be helpful to providers.

OBJECTIVES

We aggregated and analysed human SGM isolates sent to our laboratory from across the USA between 2018 and 2022 to describe their in vitro susceptibility patterns and construct an antibiogram.

METHODS

SGM isolates' species/subspecies and mutations in rrs or rrl were identified by a line probe assay. AST was done primarily by broth microdilution and interpreted using the latest CLSI guideline. Mutational and AST results for SGM with ≥15 isolates were collated and analysed with descriptive statistics.

RESULTS

There were 32 different species/subspecies of SGM from 10 131 isolates between January 2018 and December 2022 from across the USA, 80% of which were from organisms in Mycobacterium avium complex (MAC). Most specimens were sputum and came from Florida (2892). MAC ranged from 94% to 100% susceptible to clarithromycin, 64% to 91% to amikacin, 2% to 31% to linezolid, and 4% to 41% to moxifloxacin. Non-MAC SGM ranged from 82% to 100% susceptible to clarithromycin, 49% to 100% to amikacin, and 76% to 100% to rifabutin, but susceptibilities to other antimicrobials varied widely. WT rrs and rrl predicted >96% of phenotypic non-resistance to amikacin and clarithromycin, respectively, whereas mutant genotypes predicted >90% of phenotypic resistance.

CONCLUSIONS

Most SGM are likely to be susceptible to clarithromycin and amikacin, complementing their treatment guidance by mycobacterial experts. Molecular identification of resistant genotypes is accurate and helpful. This antibiogram for SGM will help providers.

Intracellular and in vivo activities of oxazolidinone drugs against Mycobacterium avium complex infection

The prevalence of Mycobacterium avium complex-pulmonary disease (MAC-PD) has become a growing concern worldwide, and current treatments involving macrolides (clarithromycin [CLR] or azithromycin), ethambutol, and rifampicin have limited success, highlighting the need for better therapeutic strategies. Recently, oxazolidinone drugs have been identified as novel anti-tuberculosis drugs effective against drug-resistant M. tuberculosis. However, the effects of these drugs against MAC are still controversial due to limited data. Here, we first evaluated the intracellular anti-MAC activities of two oxazolidinone drugs, linezolid (LZD) and delpazolid (DZD), against 10 macrolide-susceptible MAC strains and one macrolide-resistant M. avium strain in murine bone marrow-derived macrophages (BMDMs) and found that both drugs demonstrated similar potential. The synergistic efficacies with CLR were then determined in a chronic progressive MAC-PD murine model by initiating a 4-week treatment at 8 weeks post-infection. Upon assessment of bacterial burdens and inflamed lesions, oxazolidinone drugs exhibited no anti-MAC effect, and there was no significant difference in the synergistic effect of CLR between LZD and DZD. These findings suggest that oxazolidinone drugs inhibit intracellular bacterial growth, even against macrolide-resistant MAC, but their clinical application requires further consideration.

An Overview of Mycoviral Curing Strategies Used in Evaluating Fungal Host Fitness

The number of novel mycoviruses is increasing at a high pace due to advancements in sequencing technologies. As a result, an uncountable number of mycoviral sequences are available in public sequence repositories. However, only genomic information is not sufficient to understand the impact of mycoviruses on their host biology. Biological characterization is required to determine the nature of mycoviruses (cryptic, hypervirulent, or hypovirulent) and to search for mycoviruses with biocontrol and therapeutic potential. Currently, no particular selective method is used as the gold standard against these mycoviral infections. Given the importance of curing, we present an overview of procedures used in preparation of isogenic lines, along with their benefits and drawbacks. We concluded that a combination of single-spore isolation and hyphal tipping is the best fit for preparation of isogenic lines. Furthermore, recent bioinformatic approaches should be introduced in the field of mycovirology to predict virus-specific antivirals to get robust results.

Blocking ADP-ribosylation expands the anti-mycobacterial spectrum of rifamycins

The clinical utility of rifamycins against non-tuberculous mycobacterial (NTM) disease is limited by intrinsic drug resistance achieved by ADP-ribosyltransferase Arr. By blocking the site of ribosylation, we recently optimized a series of analogs with substantially improved potency against Mycobacterium abscessus. Here, we show that a representative member of this series is significantly more potent than rifabutin against major NTM pathogens expressing Arr, providing a powerful medicinal chemistry approach to expand the antimycobacterial spectrum of rifamycins. IMPORTANCE Lung disease caused by a range of different species of non-tuberculous mycobacteria (NTM) is difficult to cure. The rifamycins are very active against Mycobacterium tuberculosis, which causes tuberculosis (TB), but inactive against many NTM species. Previously, we showed that the natural resistance of the NTM Mycobacterium abscessus to rifamycins is due to enzymatic inactivation of the drug by the bacterium. We generated chemically modified versions of rifamycins that prevent inactivation by the bacterium and thus become highly active against M. abscessus. Here, we show that such a chemically modified rifamycin is also highly active against several additional NTM species that harbor the rifamycin inactivating enzyme found in M. abscessus, including M. chelonae, M. fortuitum, and M. simiae. This finding expands the potential therapeutic utility of our novel rifamycins to include several currently difficult-to-cure NTM lung disease pathogens beyond M. abscessus.

Targeted and efficient delivery of rifampicin to macrophages involved in non-tuberculous mycobacterial infection via mannosylated solid lipid nanoparticles

Non-tuberculous mycobacterial infections are representative difficult-to-cure lung diseases with high incidence. Conventional treatments have several limitations such as negative side effects and increased drug resistance due to long-term administration. To overcome these limitations, there is a growing need for more stable drug delivery systems. Among the various drug delivery platforms developed thus far, solid lipid nanoparticles can be effectively loaded with hydrophobic substances and their physicochemical properties can be easily manipulated through surface modification, which makes them highly suitable drug delivery materials. Recent studies have reported the successful development of nanoparticles capable of selectively delivering drugs by targeting lectin-like receptors overexpressed on the surface of immune cells. Among these lectin-like receptors, the mannose receptor is a promising target because it is expressed on the surface of macrophages and is involved in immune activity. This study sought to synthesize rifampicin-loaded mannose surface-modified solid lipid nanoparticles (Man-RIF SLNs). The Man-RIF SLN synthesis process was first optimized, after which the characteristics of the synthesized particles were analyzed using dynamic light scattering (DLS), nanoparticle tracking analysis (NTA), and transmission electron microscopy (TEM). The surface modification with mannose was confirmed through FT-IR analysis. More importantly, the synthesized Man-RIF SLNs exhibited antibacterial and anti-biofilm properties against Mycobacterium intracellulare, a causative agent of non-tuberculous lung disease. Therefore, this study demonstrated that mannose receptor-targeted rifampicin delivery through solid lipid nanoparticles can be effectively applied to the treatment of non-tuberculous lung disease. Moreover, Man-RIF SLNs could also be used for the targeted delivery of drugs to several types of carcinoma cells or immune cells, as well as to treat lung diseases.

Additive Effects of Cyclic Peptide [R4W4] When Added Alongside Azithromycin and Rifampicin against Mycobacterium avium Infection

Mycobacterium avium (M. avium), a type of nontuberculous mycobacteria (NTM), poses a risk for pulmonary infections and disseminated infections in immunocompromised individuals. Conventional treatment consists of a 12-month regimen of the first-line antibiotics rifampicin and azithromycin. However, the treatment duration and low antibiotic tolerability present challenges in the treatment of M. avium infection. Furthermore, the emergence of multidrug-resistant mycobacterium strains prompts a need for novel treatments against M. avium infection. This study aims to test the efficacy of a novel antimicrobial peptide, cyclic [R4W4], alongside the first-line antibiotics azithromycin and rifampicin in reducing M. avium survival. Colony-forming unit (CFU) counts were assessed after treating M. avium cultures with varying concentrations of cyclic [R4W4] alone or in conjunction with azithromycin or rifampicin 3 h and 4 days post-treatment. M. avium growth was significantly reduced 4 days after cyclic [R4W4] single treatment. Additionally, cyclic [R4W4]-azithromycin and cyclic [R4W4]-rifampicin combination treatments at specific concentrations significantly reduced M. avium survival 3 h and 4 days post-treatment compared with single antibiotic treatment alone. These findings demonstrate cyclic [R4W4] as a potent treatment method against M. avium and provide insight into novel therapeutic approaches against mycobacterium infections.

Towards clinical breakpoints for non-tuberculous mycobacteria - Determination of epidemiological cut off values for the Mycobacterium avium complex and Mycobacterium abscessus using broth microdilution

OBJECTIVE

For non-tuberculous mycobacteria (NTM), minimum inhibitory concentration (MIC) distributions of wild-type isolates have not been systematically evaluated despite their importance for establishing antimicrobial susceptibility testing (AST) breakpoints.

METHODS

We gathered MIC distributions for drugs used against the Mycobacterium avium complex (MAC) and Mycobacterium abscessus (MAB) obtained by commercial broth microdilution (SLOMYCOI and RAPMYCOI) from 12 laboratories. Epidemiological cut-off values (ECOFFs) and tentative ECOFFs (TECOFFs) were determined by EUCAST methodology including quality control (QC) strains.

RESULTS

The clarithromycin ECOFF was 16 mg/L for M. avium (n = 1271) whereas TECOFFs were 8 mg/L for M. intracellulare (n = 415) and 1 mg/L for MAB (n = 1014) confirmed by analysing MAB subspecies without inducible macrolide resistance (n = 235). For amikacin, the ECOFFs were 64 mg/L for MAC and MAB. For moxifloxacin, the WT spanned >8 mg/L for both MAC and MAB. For linezolid, the ECOFF and TECOFF were 64 mg/L for M. avium and M. intracellulare, respectively. Current CLSI breakpoints for amikacin (16 mg/L), moxifloxacin (1 mg/L) and linezolid (8 mg/L) divided the corresponding WT distributions. For QC M. avium and M. peregrinum, ≥95% of MIC values were well within recommended QC ranges.

CONCLUSION

As a first step towards clinical breakpoints for NTM, (T)ECOFFs were defined for several antimicrobials against MAC and MAB. Broad wild-type MIC distributions indicate a need for further method refinement which is now under development within the EUCAST subcommittee for anti-mycobacterial drug susceptibility testing. In addition, we showed that several CLSI NTM breakpoints are not consistent in relation to the (T)ECOFFs.

Isolation and Antimicrobial Susceptibility of Nontuberculous Mycobacteria in a Tertiary Hospital in Korea, 2016 to 2020

BACKGROUND

There is a global increase in isolation of nontuberculous mycobacteria (NTM). The aim of the study was to analyze longitudinal trends of NTM identification and pattern of antimicrobial susceptibility testing.

METHODS

NTM recovery rates, distribution of NTM species identification, and antimicrobial susceptibility pattern of NTM at Pusan National University Yangsan Hospital between January 2016 and December 2020 were retrospectively analyzed.

RESULTS

A total of 52,456 specimens from 21,264 patients were submitted for mycobacterial culture, of which 2,521 from 1,410 patients were NTM positive over five years (January 2016 to December 2020). NTM isolation showed an increasing trend from 2016 to 2020 (p<0.001, test for trend) mainly caused by Mycobacterium avium complex. The vast majority of M. avium complex were susceptible to key agents clarithromycin and amikacin. For Mycobacterium kansasii, resistance to rifampin and clarithromycin is rare. Amikacin was the most effective drug against Mycobacterium abscessus subspecies abscessus and Mycobacterium subspecies massiliense. Most of M. subspecies massiliense were susceptible to clarithromycin, while the majority of M. abscessus subspecies abscessus were resistant to clarithromycin (p<0.001).

CONCLUSION

There was an increasing trend of NTM isolation in our hospital. Resistance to key drugs was uncommon for most NTM species except for M. abscessus subspecies abscessus against clarithromycin.

Diagnosis and Management of Pulmonary NTM with a Focus on Mycobacterium avium Complex and Mycobacterium abscessus: Challenges and Prospects

BACKGROUND

Nontuberculous mycobacteria (NTM) are ubiquitous. NTM can affect different organs and may cause disseminated diseases, but the pulmonary form is the most common form. Pulmonary NTM is commonly seen in patients with underlying diseases. Pulmonary Mycobacterium avium complex (MAC) is the most common NTM disease and M. abscessus (MAB) is the most challenging to treat. This review is prepared with the following objectives: (a) to evaluate new methods available for the diagnosis of pulmonary MAC or MAB, (b) to assess advances in developing new therapeutics and their impact on treatment of pulmonary MAC or MAB, and (c) to evaluate the prospects of preventive strategies including vaccines against pulmonary MAC or MAB.

METHODS

A literature search was conducted using PubMed/MEDLINE and multiple search terms. The search was restricted to the English language and human studies. The database query resulted in a total of 197 publications. After the title and abstract review, 64 articles were included in this analysis.

RESULTS

The guidelines by the American Thoracic Society (ATS), European Respiratory Society (ERS), European Society of Clinical Microbiology and Infectious Diseases (ESCMID), and Infectious Diseases Society of America (IDSA) are widely applicable. The guidelines are based on expert opinion and there may be a need to broaden criteria to include those with underlying lung diseases who may not fulfill some of the criteria as 'probable cases' for better follow up and management. Some cases with only one culture-positive sputum sample or suggestive histology without a positive culture may benefit from new methods of confirming NTM infection. Amikacin liposomal inhalation suspension (ALIS), gallium containing compounds and immunotherapies will have potential in the management of pulmonary MAC and MAB.

CONCLUSIONS

the prevalence of pulmonary NTM is increasing. The efforts to optimize diagnosis and treatment of pulmonary NTM are encouraging. There is still a need to develop new diagnostics and therapeutics.

Variability of Mycobacterium avium Complex Isolates Drug Susceptibility Testing by Broth Microdilution

Non-tuberculous mycobacteria are widely distributed in environments and are capable of infecting humans, particularly those with a compromised immune system. The most prevalent species that cause nontuberculous mycobacterial lung diseases are slow-growing bacteria from the Mycobacterium avium complex (MAC), mainly M. avium or M. intracellulare. The key treatment of MAC infections includes macrolides, ethambutol, and rifampicin; however, the therapy outcomes are unsatisfactory. Phenotypic drug susceptibility testing is a conditional recommendation prior to treatment, and critical concentrations for clarithromycin, amikacin, moxifloxacin, and linezolid have been established. In this review, data from studies on the determination of MIC of clinical isolates using the broth microdilution method were summarized. A significant variation in the MIC distributions from different studies was found. The main reasons could impact the findings: insufficient reproducibility of the phenotypic testing and variation in species lineages identified in different laboratories, which could have various intrinsic susceptibility to drugs. For most of the drugs analyzed, the MICs are too high, which could undermine the treatment efficiency. Further improvement of treatment outcomes demands the validation of microbiological resistance criteria together with the identification of molecular mechanisms of resistance.

Antimicrobial susceptibility and minimum inhibitory concentration distribution of common clinically relevant non-tuberculous mycobacterial isolates from the respiratory tract

Objective: To determine the minimum inhibitory concentration (MIC) distribution of antibacterial drugs and the susceptibility of non-tuberculous mycobacterial (NTM) isolates to provide a reference basis for the clinical selection of an effective starting regimen.Methods: The common clinical isolates of NTM in the respiratory tract, which met the standards of the American Thoracic Society for NTM lung disease, were collected. The MICs of 81 isolates were determined using the microbroth dilution method (Thermo Fisher Scientific, USA), as recommended by the Clinical and Laboratory Standards Institute, USA.Results: Included were 43 Mycobacterium avium complex (MAC) strains, 24 M. abscessus complex (MAB) strains, and 14 M. kansasii strains. The sensitivity rates of MAC to clarithromycin and amikacin were 81.4% and 79.1%, respectively, while the sensitivity rates to linezolid and moxifloxacin were only 20.9% and 9.3%; the MIC of rifabutin was the lowest (MIC50% was just 2 μg/mL). After incubation for 3-5 days, the sensitivity rate of MAB to clarithromycin was 87.5%; this decreased to 50% after 14 days' incubation. Most of them were susceptible to amikacin (91.6%), and most were resistant to moxifloxacin (95.8%), ciprofloxacin (95.8%), imipenem (95.8%), amoxicillin/clavulanate (95.8%), tobramycin (79.1%), doxycycline (95.8%) and trimethoprim/sulfamethoxazole (95.8%). intermediate (83.3%) and resistant (16.7%) to cefoxitin. The susceptibility to linezolid was only 33.3%. The sensitivity and resistance breakpoints of tigecycline were set to ≤0.5 and ≥8 μg/mL, respectively, and the sensitivity and resistance rates were 50% and 0%, respectively. M. kansasii was susceptible to clarithromycin, amikacin, linezolid, moxifloxacin, rifampicin and rifabutin (100%).Discussion: In Wenzhou, clarithromycin, amikacin and rifabutin have good antibacterial activity against MAC, while linezolid and moxifloxacin have high resistance. Amikacin and tigecycline have strong antibacterial activity against MAB, while most other antibacterial drugs are resistant to varying degrees. Most antibacterial drugs are susceptible to M. kansasii and have good antibacterial activity.Conclusion: The identification of NTM species and the detection of their MICs have certain guiding values for the treatment of NTM lung disease.Key MessageThe three most common respiratory non-tuberculous mycobacterial (NTM) isolates with clinical significance in the Wenzhou area were tested for drug susceptibility. The broth microdilution method was used to determine the minimum inhibitory concentration distribution of antibacterial drugs and the susceptibility of NTM isolates to provide a reference basis for the clinical selection of an effective starting regimen.

In vitro assessment of 17 antimicrobial agents against clinical Mycobacterium avium complex isolates

Background

Recently, Mycobacterium avium complex (MAC) infections have been increasing, especially in immunocompromised and older adults. The rapid increase has triggered a global health concern due to limited therapeutic strategies and adverse effects caused by long-term medication. To provide more evidence for the treatment of MAC, we studied the in vitro inhibitory activities of 17 antimicrobial agents against clinical MAC isolates.

Results

A total of 111 clinical MAC isolates were enrolled in the study and they were identified as M. intracellulare, M. avium, M. marseillense, M. colombiense, M. yongonense, and two isolates could not be identified at the species level. MAC strains had relatively low (0–21.6%) resistance to clarithromycin, amikacin, bedaquiline, rifabutin, streptomycin, and clofazimine, and the resistant rates to isoniazid, rifampin, linezolid, doxycycline, and ethionamide were very high (72.1–100%). In addition, M. avium had a significantly higher resistance rate than that of M. intracellulare for ethambutol (92.3% vs 40.7%, P < 0.001), amikacin (15.4% vs 1.2%, P = 0.049), and cycloserine (69.2% vs 25.9%, P = 0.004).

Conclusions

Our results supported the current usage of macrolides, rifabutin, and aminoglycosides in the regimens for MAC infection, and also demonstrated the low resistance rate against new drugs, such as clofazimine, tedizolid, and bedaquiline, suggesting the possible implementation of these drugs in MAC treatment.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12866-022-02582-2.

Relationship between Resistance to Ethambutol and Rifampin and Clinical Outcomes in Mycobacterium avium Complex Pulmonary Disease

We evaluated the associations between the in vitro activities of ethambutol and rifampin and clinical outcomes of Mycobacterium avium complex (MAC) pulmonary disease (PD). Among 158 patients with MAC-PD, there was no relationship between high MICs for ethambutol and/or rifampin and treatment failure for MAC-PD. Ethambutol and rifampin resistance was common among MAC isolates (rates of 87% and 59%, respectively), but mutations in embB, rpoB, and rpoC were rare, with detection in only 4% of the drug-resistant MAC isolates.

Clinical Pharmacokinetic and Pharmacodynamic Considerations in the Drug Treatment of Non-Tuberculous Mycobacteria in Cystic Fibrosis

Non-tuberculous mycobacteria (NTM) are an emerging group of pulmonary infectious pathogens of increasing importance to the management of patients with cystic fibrosis (CF). NTM include slow-growing mycobacteria such as Mycobacterium avium complex (MAC) and rapidly growing mycobacteria such as Mycobacterium abscessus. The incidence of NTM in the CF population is increasing and infection contributes to significant morbidity to the patient and costs to the health system. Treating M. abscessus requires the combination of multiple costly antibiotics for months, with potentially significant toxicity associated with treatment. Although international guidelines for the treatment of NTM infection in CF are available, there are a lack of robust pharmacokinetic studies in CF patients to inform dosing and drug choice. This paper aims to outline the pharmacokinetic and pharmacodynamic factors informing the optimal treatment of NTM infections in CF.

A Clofazimine-Containing Regimen Confers Improved Treatment Outcomes in Macrophages and in a Murine Model of Chronic Progressive Pulmonary Infection Caused by the Mycobacterium avium Complex

Treatment outcomes using the standard regimen (a macrolide, ethambutol, and rifampicin) for Mycobacterium avium complex-pulmonary disease (MAC-PD) remain unsatisfactory. Thus, improved treatment regimens for MAC-PD are required. Clofazimine has recently been revisited as an effective drug against mycobacterial infection. We performed a comparison between the standard regimen and an alternative regimen (replacing the rifampicin of the standard regimen with clofazimine) based on the intracellular anti-MAC activities of the individual drugs in a murine model of chronic progressive MAC-pulmonary infection (MAC-PI). The intracellular anti-MAC activities of the individual drugs and their combinations in murine bone marrow-derived macrophages (BMDMs) were determined. The treatment efficacies of the standard and clofazimine-containing regimens were evaluated in mice chronically infected with M. avium by initiating 2- and 4-week treatment at 8 weeks post-infection. Bacterial loads in the lung, spleen, and liver were assessed along with lung inflammation. Insufficient intracellular anti-MAC activity of rifampicin in BMDMs was recorded despite its low in vitro minimum inhibitory concentrations (MICs), whereas optimal intracellular killing activity against all tested MAC strains was achieved with clofazimine. Compared to the standard regimen, the clofazimine-containing regimen significantly reduced CFUs in all organs and achieved marked reductions in lung inflammation. The replacement of rifampicin with clofazimine in the treatment regimen resulted in more favorable outcomes in an animal model of chronic progressive MAC-PI. Intriguingly, 2 weeks of treatment with the clofazimine-containing regimen reduced bacterial loads more effectively than 4 weeks of treatment with the standard regimen in M. avium-infected mice. Thus, the clofazimine-containing regimen also had a treatment-shortening effect.

Association Between Duration of Aminoglycoside Treatment and Outcome of Cavitary Mycobacterium avium Complex Lung Disease

BACKGROUND

Although aminoglycosides are recommended for cavitary Mycobacterium avium complex lung disease (MAC-LD), the optimal duration of treatment is unclear. We investigated the association between duration of aminoglycoside treatment and outcomes in cavitary MAC-LD.

METHODS

Among patients diagnosed with macrolide-susceptible cavitary MAC-LD between 2000 and 2013, 101 who received treatment up to August 2017 with a regimen containing aminoglycosides were enrolled at a tertiary referral center in South Korea. Their medical records were retrospectively reviewed. The duration of aminoglycoside treatment was at the discretion of the attending physician.

RESULTS

A total of 75 patients (74.3%) were administered aminoglycosides for ≥3 months (median 164 days), whereas the remaining 26 patients (25.7%) received treatment for <3 months (median 59 days). The overall treatment success rate was 63.4% (64/101). Patients treated with aminoglycosides for ≥3 months had a significantly higher success rate than those treated for <3 months (69.3% vs 46.2%; P = .035). Multivariate analysis revealed that aminoglycoside treatment for ≥3 months was a significant factor for treatment success (adjusted odds ratio, 3.602; 95% confidence interval, 1.249-10.390; P = .018). Recurrence occurred in 8 (22.9%) of 35 patients who were followed up for at least 3 years after the end of treatment; all 8 patients received aminoglycosides for ≥3 months.

CONCLUSIONS

Patients with cavitary MAC-LD treated with aminoglycosides for ≥3 months showed higher treatment success rate than those treated for <3 months. However, treatment for ≥3 months was not associated with the development of recurrence.

Minimal Inhibitory Concentration of Clofazimine Among Clinical Isolates of Nontuberculous Mycobacteria and Its Impact on Treatment Outcome

BACKGROUND

Clofazimine has been regarded as a promising agent for the treatment of nontuberculous mycobacteria pulmonary disease (NTM-PD). However, its overall effectiveness in vitro and in the clinic remains unknown.

RESEARCH QUESTION

What is the minimal inhibitory concentration (MIC) of clofazimine in clinical isolates and the association between MICs and treatment outcome?

STUDY DESIGN AND METHODS

MICs for clofazimine were measured in clinical isolates from NTM-PD patients who participated in a prospective study at Seoul National University Hospital. The MIC was determined by using the broth microdilution concentration method. Correlation between MIC and conversion to negative of sputum culture with clofazimine was determined.

RESULTS

Of a total 189 isolates, 133 strains were Mycobacterium avium complex (MAC) and 40 strains were M abscessus. Although the clofazimine MICs for MAC ranged from 0.031 mg/L to 8 mg/L, the values obtained for M abscessus ranged from 0.031 mg/L to 16 mg/L. Of 20 patients who were treated with a regimen including clofazimine, eight achieved negative conversion of sputum culture. All patients with isolates exhibiting clofazimine MIC values ≤ 0.25 mg/L achieved culture conversion. The likelihood of culture conversion in patients with MIC value ≤ 0.25 mg/L was much higher than that of patients with MIC value > 0.5 mg/L (OR, 39.3; P = .021).

INTERPRETATION

The MICs of clofazimine varied widely in clinical isolates from patients with NTM-PD. Negative conversion of sputum culture with clofazimine use was associated with a lower MIC value. Clofazimine use could be considered in patients with NTM-PD when the MIC value is ≤ 0.25 mg/L.

TRIAL REGISTRY

ClinicalTrials.gov; No.: NCT01616745; URL: www.clinicaltrials.gov.

Treatment Outcomes after Discontinuation of Ethambutol due to Adverse Events in Mycobacterium avium Complex Lung Disease

BACKGROUND

Long-term administration of ethambutol (EMB) for Mycobacterium avium complex lung disease (MAC-LD) sometimes leads to permanent discontinuation of EMB due to various adverse events. This study aimed to investigate treatment outcomes after discontinuation of EMB.

METHODS

Among patients diagnosed with MAC-LD between January 2001 and December 2014, 508 patients whose treatment was initiated with standard regimen until May 2018 were enrolled at a tertiary referral center in Korea. Of these 508 patients, 60 (11.8%) discontinued EMB due to various adverse effects. Among these 60 patients, treatment outcomes were analyzed for 44 patients by comparing their outcomes with those of matched subjects who received the standard treatment regimen without EMB discontinuation.

RESULTS

The mean age of the 60 patients who discontinued EMB was 64.4 years. Ocular toxicity was the most common cause of discontinuation of EMB (75.0%, 45/60). The mean duration of EMB administration before its discontinuation was 7.0 ± 4.6 months. The treatment failure rate of the 44 patients with EMB discontinuation analyzed for treatment outcome was 29.6%, which was higher than that of the matched patients who received the standard regimen (18.3%), although the difference was not significant (P = 0.095). Of these 44 patients, EMB was substituted with later-generation fluoroquinolone in 23 patients, and the treatment failure rate of these 23 patients was significantly higher than that of the matched patients who received the standard regimen (39.1% vs. 19.3%, P = 0.045).

CONCLUSION

These findings suggest that treatment outcomes are unsatisfactory in patients with MAC-LD who discontinue EMB owing to adverse events. Notably, there was a statistically significant high failure rate in patients who were prescribed fluoroquinolone to replace EMB.

Outcome of shorter treatment duration in non-cavitary nodular bronchiectatic Mycobacterium avium complex lung disease

Background

The recommended treatment duration for non-cavitary nodular bronchiectatic (NC-NB) Mycobacterium avium complex (MAC) lung disease (LD) is at least 12 months after culture conversion, but evidence supporting this is limited. This study investigated whether treatment for less than 12 months after culture conversion is acceptable in terms of recurrence rate.

Methods

The study enrolled the patients diagnosed with NC-NB MAC LD between 2001 and 2014 at a tertiary referral center in South Korea who received the standard treatment for at least 9 months after culture conversion up to October 2018. The patients were divided into a shorter treatment group (9-11 months after culture conversion) and a standard treatment group (≥12 months).

Results

Of the 228 patients enrolled, 59 (25.9%) were treated for 9-11 months after culture conversion and 169 (74.1%) for ≥12 months. The mean treatment durations after culture conversion in the shorter and standard treatment groups were 11.1 and 13.8 months, respectively (P<0.001). During median follow-up durations after the completion of treatment of 56.5 and 55.9 months, respectively, the recurrence rates in the two groups were similar, at 39.0% (23/59) and 36.7% (62/169). There were also no significant differences between the groups in the 1-year and 3-year recurrence rates.

Conclusions

Post-conversion treatment shorter than the recommended duration may be adequate in terms of recurrence rate for patients with NC-NB MAC LD who receive the standard treatment for at least 9 months after culture conversion.

Rational Choice of Antibiotics and Media for Mycobacterium avium Complex Drug Susceptibility Testing

The Clinical and Laboratory Standards Institute recommends the use of Mueller Hinton (MH) medium to perform drug susceptibility testing (DST) of Mycobacterium avium complex (MAC) using the microdilution method. For MAC, there has been no study on the impact of media on the determination of minimum inhibitory concentrations (MICs) of antibiotics other than clarithromycin. This study aimed at determining the impact of two media used for DST of MAC and at augmenting the number of pertinent MICs for MAC species encountered in clinical practice. MICs of antibiotics used for the treatment of MAC infections were determined for 158 clinical MAC isolates (80 M. avium, 40 M. intracellulare, 35 M. chimaera, two M. yongonense and one M. timonense) in MH and 7H9 broths using the SLOMYCO Sensititre^TM system (TREK Diagnostic Systems, East Grinstead, United Kingdom). The modal MICs determined in both media were the same for linezolid, moxifloxacin, rifabutin and amikacin but not for clarithromycin, rifampin and ethambutol. The kappa test for MICs converted to susceptibility categories showed an excellent agreement for clarithromycin, a moderate agreement for linezolid and a weak agreement for moxifloxacin and amikacin. For amikacin, 7H9 allowed a better distinction (fewer intermediate strains) of wild-type populations than MH. Existing breakpoints for linezolid and moxifloxacin are spread through the distribution of MICs for wild-type populations. The only breakpoints that can be used rationally are those for amikacin and clarithromycin. For amikacin, 7H9 performs better than MH, whereas both media perform equally for clarithromycin. Given that testing in 7H9, as opposed to MH, allows easier MIC measurements and yields greater reproducibility, we propose the use of 7H9 medium for DST of MAC.

The impact of the coexistence of mycobacterium avium with mycobacterium tuberculosis on the result of GeneXpert and MGIT susceptibility test

Rapid tests to diagnose tuberculosis relies on molecular detection of the M. tuberculosis. GeneXpert MTB/RIF test identifies M. tuberculosis and rifampicin resistance. We present a case of simultaneous coinfection with M. tuberculosis and M. avium. M. tuberculosis was detected in the sputum by PCR GeneXpert method. Unrecognized coexistence of M. tuberculosis and M. avium modified the results of drug susceptibility tests making the primary identification of M. tuberculosis as multi-drug resistant strain. We performed in vitro experiments to investigate the effect of the coexistence of M. avium with M. tuberculosis on the results of GeneXpert method, and drug susceptibility test.

Discontinuation rates attributed to adverse events and treatment outcomes between clarithromycin and azithromycin in Mycobacterium avium complex lung disease: A propensity score analysis

OBJECTIVES

This study aimed to compare the discontinuation rates attributed to adverse events and treatment outcomes between clarithromycin (CLR) and azithromycin (AZM) in patients with Mycobacterium avium complex lung disease (MAC-LD).

METHODS

Among patients diagnosed with MAC-LD during 2001-2013, 560 for whom treatment was initiated as a guideline-based therapy until May 2018 were selected for adverse event analysis. Of them, 316 who underwent treatment for ≥12 months were selected for outcome analysis. Their medical records were retrospectively reviewed. The discontinuation and treatment success rates were analysed after adjustments using the inverse probability of treatment weighted (IPTW) method.

RESULTS

Among the 560 patients, 466 (83.2%) and 94 (16.8%) started CLR-containing and AZM-containing regimens, respectively. The IPTW method using propensity scoring revealed that the discontinuation rate attributed to adverse events was significantly higher with CLR than AZM use (24.6% vs. 9.6%; P=0.001). The overall treatment success rate of the 316 patients who received guideline-based therapy for ≥12 months was 83.2%. Analysis adjusted by the IPTW method showed no significant difference in the treatment success rate between the use of CLR and AZM. Furthermore, 1-year and 3-year recurrence rates were similar with the two drugs (6.8% vs. 6.0%; P>0.999 and 31.0% vs. 37.5%; P=0.482, respectively).

CONCLUSIONS

These findings suggest that an AZM-containing regimen may be the better initial treatment choice for MAC-LD as it resulted in lesser discontinuation rates attributed to adverse events while offering similar patient outcomes when compared with CLR.

Sitafloxacin-Containing Regimen for the Treatment of Refractory Mycobacterium avium Complex Lung Disease

Background

Sitafloxacin (STFX) exhibits potent activity against Mycobacterium avium complex (MAC) in both in vitro and in vivo experiments. However, limited data are available for the clinical efficacy and adverse effects of STFX and the susceptibility of refractory MAC lung disease (MAC-LD) to the drug. Therefore, this study was aimed at evaluating the clinical efficacy and safety of an STFX-containing regimen for the treatment of refractory MAC-LD.

Methods

We retrospectively evaluated treatment outcomes of 31 patients with refractory MAC-LD, who received an STFX-containing regimen for ≥4 weeks between January 2010 and July 2017. Refractory MAC-LD was defined as persistent positive sputum cultures for >6 months of macrolide-based standard therapy.

Results

Clarithromycin resistance (minimum inhibitory concentration [MIC] ≥32 μg/mL) was identified in 15 patients (48%). Twelve months after receiving the STFX-containing regimen, 26% and 19% of patients showed symptomatic and radiological responses, respectively. Although STFX-associated adverse effects were noted in 9 patients, their severity was grade 1 (National Cancer Institute Common Terminology Criteria); only 1 patient discontinued STFX because of suspected gastrointestinal disturbance. Negative sputum culture conversion was achieved in 7 patients (23%). Both univariate and multivariate logistic regression analyses revealed that surgery, low STFX MIC (≤1 μg/mL), and macrolide resistance were significant predictors of negative sputum culture conversion.

Conclusions

Our results demonstrate that STFX may be effective in one-fourth of patients with refractory MAC-LD. Prospective larger studies that include the analyses of MAC are needed to determine the clinical efficacy of STFX against refractory MAC-LD.