Clofazimine-Containing Regimen for the Treatment of Mycobacterium abscessus Lung Disease

In vitro effects of the new oral β-lactamase inhibitor xeruborbactam in combination with oral β-lactams against clinical Mycobacterium abscessus isolates

Non-tuberculosis mycobacteria (NTM), particularly Mycobacterium abscessus subsp. abscessus (M. abscessus), are increasingly being recognized as etiological agents of NTM pulmonary disease. However, treatment options for M. abscessus are limited owing to their natural resistance to most antibiotics, including β-lactams. M. abscessus produces a class A β-lactamase, whose activity is inhibited by cyclic boronic acid β-lactamase inhibitors. We aimed to evaluate the in vitro effects of xeruborbactam, a cyclic boronic acid β-lactamase inhibitor, against M. abscessus when combined with five β-lactams (amoxicillin, tebipenem, cefdinir, cefuroxime, and cefoxitin). The drug susceptibilities of 43 M. abscessus clinical isolates obtained from 43 patients between August 2005 and May 2014 were tested. The MIC results for each β-lactam with or without 4 µg/mL xeruborbactam were examined. Xeruborbactam lowered the MIC90 values of tebipenem, amoxicillin, cefuroxime, and cefdinir by 5, ≥4, 3, and 3 dilutions, respectively. The MIC90 values of cefoxitin without xeruborbactam were 32 µg/mL and did not change upon the addition of xeruborbactam. The lowest MIC90 value was obtained for tebipenem with xeruborbactam. Almost all isolates had an MIC of 4 µg/mL; one isolate had an MIC of 2 µg/mL. With respect to the susceptibility to the same family drug, the number of susceptible isolates increased from 1/43 (2%) to 43/43 (100%) for tebipenem with xeruborbactam. Combining tebipenem and xeruborbactam could be considered an effective all-oral regimen that benefits outpatient treatment of M. abscessus pulmonary disease.

IMPORTANCE

Mycobacterium abscessus subsp. abscessus (M. abscessus) disease is treated in two phases; injectable drugs for initial followed by others for continuation. There is a need to develop all-oral treatment methods for M. abscessus infection, especially in the continuation phase. However, treatment options for M. abscessus are limited owing to their natural resistance to most antibiotics. This is the first report to evaluate the in vitro effects of xeruborbactam, a cyclic boronic acid β-lactamase inhibitor capable of inhibiting the class A β-lactamase produced by M. abscessus, against 43 M. abscessus clinical isolates when combined with five β-lactam antibiotics. Xeruborbactam lowered the MIC90 values of tebipenem by five dilutions, and the number of susceptible isolates increased from 1/43 (2%) to 43/43 (100%). We showed that the tebipenem-xeruborbactam combination might be of interest to explore further as a potentially effective oral regimen for outpatient treatment of M. abscessus pulmonary disease.

Drugs for treating infections caused by non-tubercular mycobacteria: a narrative review from the study group on mycobacteria of the Italian Society of Infectious Diseases and Tropical Medicine

BACKGROUND

Non-tuberculous mycobacteria (NTM) are generally free-living organism, widely distributed in the environment, with sporadic potential to infect. In recent years, there has been a significant increase in the global incidence of NTM-related disease, spanning across all continents and an increased mortality after the diagnosis has been reported. The decisions on whether to treat or not and which drugs to use are complex and require a multidisciplinary approach as well as patients' involvement in the decision process.

METHODS AND RESULTS

This review aims at describing the drugs used for treating NTM-associated diseases emphasizing the efficacy, tolerability, optimization strategies as well as possible drugs that might be used in case of intolerance or resistance. We also reviewed data on newer compounds highlighting the lack of randomised clinical trials for many drugs but also encouraging preliminary data for others. We also focused on non-pharmacological interventions that need to be adopted during care of individuals with NTM-associated diseases CONCLUSIONS: Despite insufficient efficacy and poor tolerability this review emphasizes the improvement in patients' care and the needs for future studies in the field of anti-NTM treatments.

Treatment Outcomes of Clofazimine-Containing Regimens in Severe Mycobacterium avium Complex Pulmonary Disease

Background

Clofazimine is suggested as a promising drug for the treatment of nontuberculous mycobacterial pulmonary disease. However, the role of clofazimine in severe Mycobacterium avium complex pulmonary disease (MAC-PD) remains unclear. In this study, we investigated the treatment outcomes of patients with severe MAC-PD treated with regimens containing clofazimine.

Methods

This study included patients diagnosed with severe MAC-PD at Seoul National University Hospital who underwent anti-mycobacterial treatment between 1 January 2011 and 31 December 2022. We assessed the rate of culture conversion within 6 months and microbiological cure in patients receiving clofazimine-containing regimens, considering the dose and duration of clofazimine administration.

Results

A total of 170 patients with severe MAC-PD, treated with regimens containing clofazimine, were included in the analysis. The median age of patients was 68 years (interquartile range, 59-75 years), with a female predominance (n = 114 [67.1%]). Cavities were identified in 121 patients (71.2%). Within 6 months, 77 patients (45.3%) achieved culture conversion, and 84 of 154 (54.6%) patients attained microbiological cure. The dose of clofazimine (100 mg vs 50 mg) was not associated with culture conversion (adjusted odds ratio [aOR], 0.64 [95% confidence interval {CI}, .29-1.42]) or microbiological cure (aOR, 1.21 [95% CI, .52-2.81]). The microbiological cure rate reached 71.0% when clofazimine was administered for 6-12 months, compared to 23.1% when administered for <6 months.

Conclusions

Clofazimine demonstrated a relatively favorable efficacy in severe MAC-PD, regardless of the maintenance dose. This effect was more pronounced when administered for a duration exceeding 6 months.

[A pharmacologic approach to treatment of Mycobacterium abscessus pulmonary disease]

Mycobacterium abscessus is a fast-growing non-tuberculous mycobacteria complex causing pulmonary infections, comprising the subspecies abscessus, massiliense and bolletii. Differences are based predominantly on natural inducible macrolide resistance, active in most Mycobacterium abscessus spp abscessus species and in Mycobacterium abscessus spp bolletii but inactive in Mycobacterium abscessus spp massiliense. Therapy consists in long-term treatment, combining multiple antibiotics. Prognosis is poor, as only 40% of patients experience cure. Pharmacodynamic and pharmacokinetic data on M. abscessus have recently been published, showing that therapy ineffectiveness might be explained by intrinsic bacterial resistance (macrolides…) and by the unfavorable pharmacokinetics of the recommended antibiotics. Other molecules and inhaled antibiotics are promising.

Treatment Approaches to Mycobacterium abscessus Pulmonary Disease

Mycobacterium abscessus pulmonary disease is highly antibiotic-resistant, and the current armamentarium of antibiotics yields poor treatment outcomes with significant drug toxicity. Macrolide susceptibility is a key prognostic factor. Optimal drug combinations, duration of therapy, and management of refractory disease are unknown. Surgical resection, performed at centers with experience in surgical management of nontuberculous mycobacterial pulmonary disease, may produce favorable outcomes in select patients. Multiple emerging therapeutic candidates hold promise for more efficacious and tolerable treatment options.

Treatment of Mycobacterium avium Complex Pulmonary Disease: When Should I Treat and What Therapy Should I Start?

Treatment of M avium pulmonary disease requires a three-drug, macrolide-based regimen that is administered for 12 months beyond culture conversion. The regimen can be administered 3 days a week in non-cavitary, nodular bronchiectatic disease but should be given daily when cavitary disease is present. For treatment refractory disease, amikacin liposome inhalation suspension is added to the regimen. Parenteral amikacin or streptomycin should be administered in the setting of extensive radiographic involvement or macrolide resistance. Recurrence of disease is common and often due to reinfection. Novel and repurposed agents are being evaluated in clinical trials.

A narrative review of nontuberculous mycobacterial pulmonary disease: microbiology, epidemiology, diagnosis, and management challenges

INTRODUCTION

Nontuberculous mycobacteria (NTM) are a diverse group of mycobacterial species that are ubiquitous in the environment. They are opportunistic pathogens that can cause a range of diseases, especially in individuals with underlying structural lung disease or compromised immune systems.

AREAS COVERED

This paper provides an in-depth analysis of NTM infections, including microbiology, environmental sources and transmission pathways, risk factors for disease, epidemiology, clinical manifestations and diagnostic approaches, guideline-based treatment recommendations, drugs under development, and management challenges.

EXPERT OPINION

Future approaches to the management of NTM pulmonary disease will require therapies that are well tolerated, can be taken for a shorter time period and perhaps less frequently, have few drug-drug interactions, and are active against the various strains of pathogens. As the numbers of infections increase, such therapies will be welcomed by clinicians and patients.

In Vitro Synergistic Effects of Omadacycline with Other Antimicrobial Agents against Mycobacterium abscessus

The clinical importance of Mycobacterium abscessus species (MABS) infections has been increasing. However, the standard treatment regimens recommended in the current guidelines often result in unfavorable outcomes. Therefore, we investigated the in vitro activity of omadacycline (OMC), a novel tetracycline, against MABS to explore its potential as a novel therapeutic option. The drug susceptibilities of 40 Mycobacterium abscessus subsp. abscessus (Mab) clinical strains obtained from the sputum of 40 patients from January 2005 to May 2014 were investigated. The MIC results for OMC, amikacin (AMK), clarithromycin (CLR), clofazimine (CLO), imipenem (IPM), rifabutin (RFB), and tedizolid (TZD) alone and their combined effects (with OMC) were examined using the checkerboard method. Additionally, we studied the differences in the effectiveness of the antibiotic combinations based on the colony morphotype of Mab. The MIC50 and MIC90 of OMC alone were 2 and 4 μg/mL, respectively. The combinations of OMC with AMK, CLR, CLO, IPM, RFB, and TZD showed synergy against 17.5%, 75.8%, 25.0%, 21.1%, 76.9%, and 34.4% of the strains, respectively. Additionally, OMC combined with CLO (47.1% versus 9.5%, P = 0.023) or TZD (60.0% versus 12.5%, P = 0.009) showed significantly higher synergy against strains with rough morphotypes than those with smooth morphotypes. In conclusion, the checkerboard analyses revealed that the synergistic effects of OMC were observed most frequently with RFB, followed by CLR, TZD, CLO, IPM, and AMK. Furthermore, OMC tended to be more effective against rough-morphotype Mab strains.

Development of Low-Cost, Weight-Adjustable Clofazimine Mini-Tablets for Treatment of Tuberculosis in Pediatrics

Clofazimine (CFZ) is an important component of the World Health Organization's (WHO) recommended all-oral drug regimen for treatment of multi-drug resistant tuberculosis (MDR-TB). However, the lack of a dividable oral dosage form has limited the use of the drug in pediatric populations, who may require lowering of the dose to reduce the likelihood of adverse drug events. In this study, pediatric-friendly CFZ mini-tablets were prepared from micronized powder via direct compression. Rapid disintegration and maximized dissolution in GI fluids was achieved using an iterative formulation design process. Pharmacokinetic (PK) parameters of the optimized mini-tablets were obtained in Sprague-Dawley rats and compared against an oral suspension of micronized CFZ particles to examine the effect of processing and formulation on the oral absorption of the drug. Differences in maximum concentration and area under the curve between the two formulations were non-significant at the highest dosing level tested. Variability between rats prevented bioequivalence from being determined according to guidelines outlined by the Food and Drug Administration (FDA). These studies provide an important proof-of-concept for an alternative, low-cost formulation and processing approach for the oral delivery of CFZ in manner that is suitable for children as young as 6 months of age.

The synergetic effect of sitafloxacin-arbekacin combination in the Mycobacterium abscessus species

Mycobacterium abscessus species (MABS) is the most commonly isolated rapidly growing mycobacteria (RGM) and is one of the most antibiotic-resistant RGM with rapid progression, therefore, treatment of MABS is still challenging. We here presented a new combination treatment with sitafloxacin that targeted rough morphotypes of MABS, causing aggressive infections. Thirty-four clinical strains of MABS were isolated from various clinical samples at the Juntendo university hospital from 2011 to 2020. The susceptibility to a combination of sitafloxacin and antimicrobial agents was compared to that of the antimicrobial agents alone. Out of 34 MABS, 8 strains treated with sitafloxacin-amikacin combination, 9 of sitafloxacin-imipenem combination, 19 of sitafloxacin-arbekacin combination, and 9 of sitafloxacin-clarithromycin combination showed synergistic effects, respectively. Sitafloxacin-arbekacin combination also exhibited the synergistic effects against 10 of 22 Mycobacterium abscessus subspecies massiliense (Mma) strains and 8 of 11 Mycobacterium abscessus subspecies abscessus (Mab) strains, a highly resistant subspecies of MABS. The sitafloxacin-arbekacin combination revealed more synergistic effects in rough morphotypes of MABS (p = 0.008). We demonstrated the synergistic effect of the sitafloxacin-arbekacin combination against MABS. Further, this combination regimen might be more effective against Mab or rough morphotypes of MABS.

Contemporary Pharmacotherapies for Nontuberculosis Mycobacterial Infections: A Narrative Review

Nontuberculous mycobacteria (NTM) are a group of atypical bacteria that may cause a spectrum of clinical manifestations, including pulmonary, musculoskeletal, skin and soft tissue, and cardiac infections. Antimycobacterial medication regimens for NTM infections require multiple agents with prolonged treatment courses and are often associated with poor tolerance in patients and suboptimal clinical outcomes. This review summarizes NTM pharmacotherapy, including treatment concepts, preferred medication regimens according to NTM species and site of infection, and emerging treatment methods for difficult-to-treat species.

Improving the Antimycobacterial Drug Clofazimine through Formation of Organic Salts by Combination with Fluoroquinolones

This work reports the synthesis, structural and thermal analysis, and in vitro evaluation of the antimicrobial activity of two new organic salts (OSs) derived from the antimycobacterial drug clofazimine and the fluoroquinolones ofloxacin or norfloxacin. Organic salts derived from active pharmaceutical ingredients (API-OSs), as those herein disclosed, hold promise as cost-effective formulations with improved features over their parent drugs, thus enabling the mitigation of some of their shortcomings. For instance, in the specific case of clofazimine, its poor solubility severely limits its bioavailability. As compared to clofazimine, the clofazimine-derived OSs now reported have improved solubility and thermostability, without any major deleterious effects on the drug's bioactivity profile.

Why Matter Matters: Fast-Tracking Mycobacterium abscessus Drug Discovery

Unlike Tuberculosis (TB), Mycobacterium abscessus lung disease is a highly drug-resistant bacterial infection with no reliable treatment options. De novo M. abscessus drug discovery is urgently needed but is hampered by the bacterium's extreme drug resistance profile, leaving the current drug pipeline underpopulated. One proposed strategy to accelerate de novo M. abscessus drug discovery is to prioritize screening of advanced TB-active compounds for anti-M. abscessus activity. This approach would take advantage of the greater chance of homologous drug targets between mycobacterial species, increasing hit rates. Furthermore, the screening of compound series with established structure-activity-relationship, pharmacokinetic, and tolerability properties should fast-track the development of in vitro anti-M. abscessus hits into lead compounds with in vivo efficacy. In this review, we evaluated the effectiveness of this strategy by examining the literature. We found several examples where the screening of advanced TB chemical matter resulted in the identification of anti-M. abscessus compounds with in vivo proof-of-concept, effectively populating the M. abscessus drug pipeline with promising new candidates. These reports validate the screening of advanced TB chemical matter as an effective means of fast-tracking M. abscessus drug discovery.

Pharmacokinetics and Adverse Effects of Clofazimine in the Treatment of Pulmonary Non-Tuberculous Mycobacterial Infection

Clofazimine (CFZ) is used to treat pulmonary non-tuberculous mycobacterial (NTM) infection; however, its pharmacokinetics remain unexplored in patients with pulmonary NTM, and the relationship between CFZ serum concentration and adverse effects has not been investigated. The objectives of this study were to characterize the pharmacokinetics of CFZ in pulmonary NTM disease treatment and to investigate the relationship between the steady-state CFZ serum concentration and adverse effects. A prospective observational study was conducted on 45 patients with pulmonary NTM treated with CFZ (UMIN000041053). A maximum of five serum samples per patient were taken at the CFZ trough, and serum concentration was measured using high-performance liquid chromatography-mass spectrometry (HPLC-MS). The pharmacokinetics of CFZ were analyzed using a nonlinear mixed effect model. The relationships among steady-state CFZ serum concentration and adverse effects, pigmentation, and heart rate-corrected QT (QTc) interval were investigated. Twenty-six patients had M. avium or M. intracellulare infection and nineteen had M. abscessus infection. The primary CFZ dosage was 50 mg/day. The estimated apparent CFZ clearance, apparent volume of distribution, and half-life were 2.4 L/h, 2,960 L, and 36 days, respectively. The combined use of rifampicin and CFZ significantly reduced CFZ exposure by 22%. Although there was no relationship between CFZ serum concentration and pigmentation intensity, the QTc interval was significantly correlated with CFZ serum concentration. The estimation of accurate pharmacokinetics for CFZ required approximately 5 months of monitoring. The relationship between the serum concentration and specific adverse effects of CFZ confirmed that CFZ serum concentration was not associated with pigmentation but did affect the QTc interval.

Antibiotic Maintenance and Redevelopment of Nontuberculous Mycobacteria Pulmonary Disease after Treatment of Mycobacterium avium Complex Pulmonary Disease

Limited data are available regarding the impact of the antibiotic maintenance period on the redevelopment of nontuberculous mycobacteria-pulmonary disease (NTM-PD) after microbiological cure of Mycobacterium avium complex (MAC)-PD. This retrospective study included 631 MAC-PD patients who achieved microbiological cure between 1994 and 2021. Data on the antibiotic maintenance period, defined as the time between culture conversion and treatment completion, were collected. Redevelopment, the subsequent diagnosis of NTM-PD regardless of causative organism after microbiological cure, was investigated. Factors associated with redevelopment were analyzed after adjusting for disease severity using the body mass index, age, cavity, erythrocyte sedimentation rate, and sex (BACES) scoring system. In total, 205 (33%) patients experienced redevelopment, with a median maintenance period after culture conversion of 15.0 months (interquartile range, 13.0 to 22.0 months). A greater proportion of patients with the nodular bronchiectatic form of MAC-PD (87% versus 80%, P = 0.033) and a longer maintenance period (median 15.0 versus 14.0 months, P < 0.001) were noted in the redevelopment group compared with the nonredevelopment group. The cumulative rate of redevelopment according to the maintenance period did not differ between the >12-month and ≤12-month groups in the total patient population or the subgroups sorted according to BACES severity. No association between a maintenance period >12 months and redevelopment was identified in multivariate models. Extending the antibiotic maintenance period more than 12 months did not reduce the redevelopment rate even with adjustment for disease severity, suggesting the need to further optimize the duration of the antibiotic maintenance period.

IMPORTANCE Limited data are available regarding the impact of the antibiotic maintenance period on the redevelopment of Mycobacterium avium complex-pulmonary (MAC-PD) disease after microbiological cure. To improve treatment outcomes and reduce the recurrence rate, current guidelines recommend maintenance of antibiotics for a minimum of 12 months after achievement of negative culture conversion. However, the optimal duration of antibiotic therapy for MAC-PD is not currently known. Moreover, in real-world clinical practice, total antibiotic duration is mainly impacted by the length of the maintenance period; however, it is unknown whether extending the maintenance period is beneficial for preventing redevelopment of NTM-PD. Our study may help to address concerns regarding the antibiotic maintenance period after achievement of negative culture conversion in patients with MAC-PD.

Mycobacterium abscessus: It’s Complex

Mycobacterium abscessus (M. abscessus) is an opportunistic pathogen usually colonizing abnormal lung airways and is often seen in patients with cystic fibrosis. Currently, there is no vaccine available for M. abscessus in clinical development. The treatment of M. abscessus-related pulmonary diseases is peculiar due to intrinsic resistance to several commonly used antibiotics. The development of either prophylactic or therapeutic interventions for M. abscessus pulmonary infections is hindered by the absence of an adequate experimental animal model. In this review, we outline the critical elements related to M. abscessus virulence mechanisms, host–pathogen interactions, and treatment challenges associated with M. abscessus pulmonary infections. The challenges of effectively combating this pathogen include developing appropriate preclinical animal models of infection, developing proper diagnostics, and designing novel strategies for treating drug-resistant M. abscessus.

Structural Characterization of Mycobacterium abscessus Phosphopantetheine Adenylyl Transferase Ligand Interactions: Implications for Fragment-Based Drug Design

Anti-microbial resistance is a rising global healthcare concern that needs urgent attention as growing number of infections become difficult to treat with the currently available antibiotics. This is particularly true for mycobacterial infections like tuberculosis and leprosy and those with emerging opportunistic pathogens such as Mycobacterium abscessus, where multi-drug resistance leads to increased healthcare cost and mortality. M. abscessus is a highly drug-resistant non-tuberculous mycobacterium which causes life-threatening infections in people with chronic lung conditions such as cystic fibrosis. In this study, we explore M. abscessus phosphopantetheine adenylyl transferase (PPAT), an enzyme involved in the biosynthesis of Coenzyme A, as a target for the development of new antibiotics. We provide structural insights into substrate and feedback inhibitor binding modes of M. abscessus PPAT, thereby setting the basis for further chemical exploration of the enzyme. We then utilize a multi-dimensional fragment screening approach involving biophysical and structural analysis, followed by evaluation of compounds from a previous fragment-based drug discovery campaign against M. tuberculosis PPAT ortholog. This allowed the identification of an early-stage lead molecule exhibiting low micro molar affinity against M. abscessus PPAT (K_d 3.2 ± 0.8 µM) and potential new ways to design inhibitors against this enzyme. The resulting crystal structures reveal striking conformational changes and closure of solvent channel of M. abscessus PPAT hexamer providing novel strategies of inhibition. The study thus validates the ligandability of M. abscessus PPAT as an antibiotic target and identifies crucial starting points for structure-guided drug discovery against this bacterium.

In Vitro Bedaquiline and Clofazimine Susceptibility Testing in Mycobacterium abscessus

Bedaquiline and clofazimine are increasingly used to treat infections with Mycobacterium abscessus. We determined distributions of MICs by broth microdilution for bedaquiline and clofazimine for 61 M. abscessus clinical isolates using different media and incubation times. We show that incubation time and growth media critically influence the MIC. Our data will aid in defining future clinical breakpoints for in vitro susceptibility testing for bedaquiline and clofazimine in M. abscessus.

Minimum Inhibitory Concentrations before and after Antibacterial Treatment in Patients with Mycobacterium abscessus Pulmonary Disease

The clinical importance of Mycobacterium abscessus (MABS) pulmonary disease has been increasing. However, there is still a lack of information about MIC distribution patterns and changes in clinical practice settings. The MIC results of rapidly growing mycobacteria isolated from 92 patients with nontuberculous mycobacterial pulmonary disease diagnosed from May 2019 to March 2021 were retrospectively analyzed. Most of the patients (86 patients; 93.5%) were infected with MABS; 46 with Mycobacterium abscessus subsp. abscessus (Mab), and 40 with Mycobacterium abscessus subsp. massiliense (Mma). Significant differences in susceptibility to clarithromycin (15.2% versus 80.0%, P < 0.001) and azithromycin (8.7% versus 62.5%, P < 0.001) were observed between Mab and Mma. Most isolates were susceptible to amikacin (80; 93.0%), and over half were susceptible to linezolid (48; 55.8%). Only one-quarter of isolates (22, 25.6%) were susceptible to imipenem, while more than half (56; 65.1%) had intermediate susceptibility. Fifty-one isolates (59.3%) had MIC values of less than 1 μg/mL for sitafloxacin, which were significantly higher than isolates for moxifloxacin (5; 5.8%), especially in Mab. Sixty-five (75.6%) isolates had MICs of less than 0.5 μg/mL to clofazimine. Two patients showed obvious MIC result changes: from susceptible to resistant to clarithromycin and from resistant to susceptible to amikacin and imipenem. In conclusion, MABS isolates were relatively susceptible to amikacin and linezolid, and clarithromycin and azithromycin were especially effective against Mma. In addition, sitafloxacin and clofazimine had low MICs and might be effective treatment agents. IMPORTANCE The MICs of isolates from 86 patients with Mycobacterium abscessus (MABS); 46 with Mycobacterium abscessus subsp. abscessus (Mab), and 40 with Mycobacterium abscessus subsp. massiliense (Mma) were retrospectively analyzed. The main findings are as follows: (i) Mma were significantly more susceptible to clarithromycin and azithromycin than Mab, and both subspecies tended to be more susceptible to clarithromycin than azithromycin. (ii) Most isolates were susceptible to amikacin (93.0%), and over half to linezolid (55.8%). (iii) Fifty-one isolates (59.3%) had MIC values of less than 1 μg/mL for sitafloxacin, and 65 (75.6%) had less than 0.5 μg/mL for clofazimine, which seems worth clinical investigating. (iv) Among nine cases analyzed chronological changes, only two patients showed obvious MIC result changes even after the long-term multidrug treatment. The present study revealed MICs of MABS clinical isolates before and after treatment in clinical settings, which could help develop future MABS treatments strategies.

Potency of omadacycline against Mycobacteroides abscessus clinical isolates in vitro and in a mouse model of pulmonary infection

The incidence of nontuberculous mycobacterial diseases in the United States is rising and has surpassed that of tuberculosis. Most notable among the nontuberculous mycobacteria is Mycobacteroides abscessus, an emerging environmental opportunistic pathogen capable of causing chronic infections. M. abscessus disease is difficult to treat, and the current treatment recommendations include repurposed antibiotics, several of which are associated with undesirable side effects. In this study, we have evaluated the activity of omadacycline, a new tetracycline derivative, against M. abscessus using in vitro and in vivo approaches. Omadacycline exhibited an MIC₉₀ of 0.5 µg/mL against a panel of 32 contemporary M. abscessus clinical isolates, several of which were resistant to antibiotics that are commonly used for treatment of M. abscessus disease. Omadacycline combined with clarithromycin, azithromycin, cefdinir, rifabutin, or linezolid also exhibited synergism against several M. abscessus strains and did not exhibit antagonism when combined with an additional nine antibiotics also commonly considered to treat M. abscessus disease. Concentration-dependent activity of omadacycline was observed in time-kill assessments. Efficacy of omadacycline was evaluated in a mouse model of lung infection against four M. abscessus strains. A dose equivalent to the 300-mg standard oral human dose was used. Compared to the untreated control group, within 4 weeks of treatment, 1 to 3 log₁₀ fewer M. abscessus CFU were observed in the lungs of mice treated with omadacycline. Treatment outcome was biphasic, with bactericidal activity observed after the first 2 weeks of treatment against all four M. abscessus strains.

Nontuberculous mycobacterial lung disease caused by Mycobacterium avium complex - disease burden, unmet needs, and advances in treatment developments

INTRODUCTION

Nontuberculous mycobacterial (NTM) lung disease (LD) is the most common clinical manifestation of NTM infection and is a growing health concern. Up to 85% of NTM-LD cases are caused by Mycobacterium avium complex (MAC). Increased awareness of NTM-LD caused by MAC is needed as patients with this disease experience substantial burden and unmet treatment needs.

AREAS COVERED

This review provides clinicians and regulatory and healthcare decision makers an overview of the clinical, economic, and humanistic burden of NTM-LD and the unmet treatment needs faced by patients and clinicians. The review focuses on NTM-LD caused by MAC. A summary of the 2020 NTM guidelines specifically for MAC-LD and an overview of novel treatment options, including amikacin liposome inhalation suspension (ALIS) as the first approved therapy for refractory MAC-LD, and investigational drugs in testing phase are provided.

EXPERT OPINION

Key advancements in NTM-LD management include recent updates to clinical practice guidelines, approval of ALIS for the treatment of refractory MAC-LD, and ongoing clinical trials of investigational treatments. Yet opportunities still exist to improve patient outcomes, including development of better screening tools, such as reliable and responsive biomarkers to help identify high-risk patients, and addressing unmet treatment needs.

In Vitro Activity and Clinical Outcomes of Clofazimine for Nontuberculous Mycobacteria Pulmonary Disease

Limited data are available regarding the in vitro activity of clofazimine against nontuberculous mycobacteria (NTM) or on outcomes of clofazimine-containing regimens in NTM-pulmonary disease (PD). Therefore, we evaluated the in vitro activity of clofazimine and the clinical outcomes of clofazimine-containing regimens. We evaluated clofazimine in vitro activity for 303 NTM isolates from NTM-PD patients. Fifty-seven clarithromycin-resistant and 35 amikacin-resistant isolates were also analyzed. Culture conversion after a 12-month treatment regimen containing clofazimine was evaluated in 58 NTM-PD patients, including 20 patients with drug-resistant isolates. Most of the 303 isolates (238/303) had minimum inhibitory concentrations (MICs) ≤ 0.25 µg/mL for clofazimine (57/63 Mycobacterium avium, 53/57 M. intracellulare, 49/52 M. kansasii, 22/64 M. abscessus, and 57/67 M. massiliense). For the 57 clarithromycin-resistant and 35 amikacin-resistant isolates, most had MICs ≤ 0.25 µg/mL (47/57 and 32/35, respectively). Among the 38 NTM-PD patients without resistance to clarithromycin or amikacin, 47% achieved culture conversion (8/27 M. abscessus, 9/9 M. massiliense, 0/1 M. avium, and 1/1 M. intracellulare). The conversion rate was higher in the MIC ≤ 0.25 µg/mL group than in the MIC = 0.5 µg/mL group (13/18 vs. 5/20, p = 0.004), and an MIC ≤ 0.25 µg/mL remained a significant factor in multivariable analysis. Culture conversion was achieved in 20% of 20 patients with clarithromycin- or amikacin-resistant isolates. However, a clofazimine MIC ≤ 0.25 µg/mL was not significant for culture conversion in the 58 NTM-PD patients, regardless of the drug resistance pattern. Clofazimine was effective in vitro against NTM species. Some patients on clofazimine-containing regimens achieved culture conversion.

Current Molecular Therapeutic Agents and Drug Candidates for Mycobacterium abscessus

Mycobacterium abscessus has been recognised as a dreadful respiratory pathogen among the non-tuberculous mycobacteria (NTM) because of misdiagnosis, prolonged therapy with poor treatment outcomes and a high cost. This pathogen also shows extremely high antimicrobial resistance against current antibiotics, including the anti-tuberculosis agents. Therefore, current chemotherapies require a long curative period and the clinical outcomes are not satisfactory. Thus, there is an urgent need for discovering and developing novel, more effective anti-M. abscessus drugs. In this review, we sum the effectiveness of the current anti-M. abscessus drugs and drug candidates. Furthermore, we describe the shortcomings and difficulties associated with M. abscessus drug discovery and development.

Radiographic severity and treatment outcome of Mycobacterium abscessus complex pulmonary disease

INTRODUCTION

The lack of reliable predictors for the treatment response complicates decisions to initiate treatment in patients with Mycobacterium abscessus complex pulmonary disease (MABC-PD). We aimed to investigate whether baseline radiographic disease severity is associated with treatment outcome in MABC-PD.

METHOD

We retrospectively analyzed 101 patients with MABC-PD (54 with M. abscessus-PD and 47 with M. massiliense-PD) treated in a tertiary referral hospital between January 2006 and December 2019. Using chest computed tomography images, baseline radiographic disease severity was quantitatively scored according to five categories of radiographic lesions (bronchiectasis, bronchiolitis, cavities, nodules, and consolidation).

RESULTS

Treatment success was achieved in 53.7% of patients with M. abscessus-PD and 85.1% of patients with M. massiliense-PD. Higher overall scores for baseline radiographic disease severity were associated with treatment failure in patients with M. massiliense-PD (aOR 1.35, 95% CI 1.02-1.79 for each 1-point increase in severity score), as well as in patients with M. abscessus-PD (aOR 1.15, 95% CI 1.00-1.33). This was particularly prominent in patients with overall severity score of ≥14 (aOR 31.16, 95% CI 1.12-868.95 for M. massiliense-PD and aOR 3.55, 95% CI 1.01-12.45 for M. abscessus-PD). Among variable radiographic abnormalities, the score for cavitary lesion severity was associated with treatment failure in patients with M. abscessus-PD (aOR 1.26, 95% CI 1.01-1.56), but not in patients with M. massiliense-PD.

CONCLUSIONS

Given the association between baseline radiographic disease severity and treatment outcome, initiating treatment should be actively considered before significant progression of radiographic lesions in patients with MABC-PD.

Treatment of Mycobacterium abscessus Pulmonary Disease

Mycobacterium abscessus is the second most common nontuberculous mycobacterial lung disease pathogen and comprises three subspecies: abscessus, massiliense, and bolletii. Subspecies identification is critical for disease management, as subspecies abscessus and bolletii have an inducible macrolide resistance gene [erm(41)] that results in clinical macrolide resistance. In contrast, subspecies massiliense does not have an active erm(41) gene and is therefore susceptible in vitro and clinically to macrolide-containing regimens. M abscessus is also vulnerable to acquired mutational macrolide resistance. Macrolide resistance has such a profoundly negative impact on M abscessus treatment response that preserving macrolide susceptibility with adequate companion drugs for macrolides is among the highest treatment priorities. After the macrolides, amikacin is regarded as the next most important drug for M abscessus treatment, although data validating that assertion are lacking. The considerations for preventing acquired macrolide resistance also apply to amikacin. Recent guidelines suggest that treatment should be guided by in vitro susceptibilities but, aside from macrolides and amikacin, no other antibiotics have a validated minimum inhibitory concentration for M abscessus. Currently, phase therapy (intensive and continuation) is recommended for M abscessus. This approach is successful with macrolide-susceptible M abscessus but not with macrolide-resistant M abscessus, in which even more aggressive therapy is not predictably successful. Newer drugs have become available, with encouraging in vitro activity against M abscessus, but in vivo validation of their superiority to current agents is not yet available. In the absence of unequivocally effective regimens, we offer suggestions for managing this treatment-refractory organism.

Clofazimine for treatment of multidrug-resistant non-tuberculous mycobacteria

BACKGROUND

/QUESTION: Nontuberculous mycobacteria (NTM) infections are increasingly detected but difficult to cure given complex drug-resistance patterns. Select U.S. centers have incorporated clofazimine in the treatment of NTM but experience is limited as procurement restrictions hamper widespread use.

METHODS

A prospective cohort study was performed in patients diagnosed with pulmonary or extrapulmonary NTM infection and treated with clofazimine between February 2015 and April 2019 at a tertiary referral hospital. Treatment success was defined by a combined outcome of clinical stabilization, microbiologic cure and radiologic improvement. Secondary outcomes included all-cause mortality and time to sputum culture conversion. Uni/multi-variate regression were used to define associations between pre-determined predictor variables and overall treatment outcome.

RESULTS

Of 44 patients enrolled, 39 (89 %) received clofazimine along with a median of 3 concomitant antibiotics. Thirty-one (80 %) of patients had pulmonary NTM infection, with Mycobacterium abscessus group and Mycobacterium avium complex being the most common species groups identified. Of 36 people with evaluable outcomes, 35 (97 %) survived and 22 (58 %) had treatment success, including 12 of 19 (63 %) with Mycobacterium abscessus group. In multivariate analysis, patients with Mycobacterium abscessus group were more likely to experience treatment success (OR 18.22, 95%CI 0.972-341.43, p = 0.052), while macrolide resistance predicted a lack of treatment success (OR 0.053, 95%CI 0.003-0.841, p = 0.037). Clofazimine was well-tolerated.

CONCLUSION

Adding clofazimine to multi-class antibiotic regimens for drug-resistant NTM infection led to treatment success in the majority treated. Randomized controlled studies are needed to determine the individual impact of clofazimine within an otherwise optimized drug regimen.

In vitro susceptibility of Mycobacterium abscessus complex and feasibility of standardizing treatment regimens

OBJECTIVES

To determine the in vitro susceptibility of members of the Mycobacterium abscessus complex to routinely tested antibiotics and to an extended antibiotic panel.

METHODS

Non-duplicate isolates for which susceptibility testing results were available were included in this study. Retrospective laboratory records were reviewed, including tigecycline susceptibility results, and testing was performed with additional drugs, including vancomycin, dalbavancin, telavancin, oritavancin, rifabutin, delafloxacin, eravacycline, clofazimine and bedaquiline using broth microdilution (Sensititre, Thermo Fisher).

RESULTS

A total of 218 M. abscessus complex isolates were included for retrospective review, of which 151 were respiratory isolates. Of these 218 isolates, 211 were available for additional testing with the extended antibiotic panel. Of these, 146 were respiratory isolates. One isolate had a vancomycin MIC of 2 mg/L and MICs of all other isolates were >8 mg/L. All isolates had MICs of >8 mg/L for oritavancin, dalbavancin and telavancin. One isolate had a delafloxacin MIC of 4 mg/L and MICs of all other isolates were >8 mg/L. The MIC50/MIC90s of rifabutin, tigecycline, eravacycline, clofazimine and bedaquiline were 16/32, 0.5/1, 0.12/0.25, 0.12/0.25 and 0.06/0.12 mg/L, respectively.

CONCLUSIONS

In vitro activity was demonstrated for clofazimine, bedaquiline and eravacycline, indicating potential for inclusion as standardized therapy for M. abscessus complex infections.

Invasive Mycobacterium abscessus Outbreak at a Pediatric Dental Clinic

Background

Mycobacterium species, specifically M. abscessus and M. chelonae (MABs), are known to contaminate water systems and are uncommon causes of health care–associated infection, but morbidity can be significant and treatment complex.

Methods

Odontogenic MAB infections occurred in patients following pulpotomy procedures at dental clinic A from 1 January to 6 September 2016. We identified confirmed and probable cases using culture data, imaging, pathology results, and surgical findings. Epidemiologic and clinical data including demographics, symptoms, laboratory findings, treatment regimens, and outcomes were extracted.

Results

Of 1082 at-risk patients, 71 case patients (22 confirmed; 49 probable) were identified. Median age was 6 years. Median symptom onset was 85 days postpulpotomy. Pain and/or swelling on admission occurred in 79%. On imaging, 49 of 70 had abnormalities of the mandible or maxilla, 13 of 70 had lymphadenopathy, and 19 of 68 had pulmonary nodules. Seventy were hospitalized (average of 8.5 days). Intravenous antibiotics were administered to 32 cases for a median length of 137 days. Clofazimine was administered to 29 patients as part of their multidrug regimen. Antibiotic treatment was associated with many adverse effects. Treated children showed evidence of jaw healing with resolved/improving pulmonary nodules at 1-year follow-up.

Conclusions

This is the largest outbreak of invasive MAB infections associated with a pediatric dental practice. While infections were indolent, patients suffered medical and surgical consequences of treatment, including permanent tooth loss. Identification of this outbreak led to a change in water standards for pediatric dental procedures in California. Enhanced national dental water quality standards are needed to prevent future outbreaks.

Tedizolid vs Linezolid for the Treatment of Nontuberculous Mycobacteria Infections in Solid Organ Transplant Recipients

Background

Treatment options for nontuberculous mycobacteria (NTM) infections are limited by the pathogen's intrinsic resistance profile and toxicities. Tedizolid and linezolid display in vitro activity against NTM species. However, safety data and treatment outcomes are limited in the solid organ transplant (SOT) population.

Methods

This was a single-center retrospective cohort study of adult SOT recipients receiving linezolid or tedizolid for an NTM infection from January 1, 2010, to August 31, 2019. The primary outcome compared the hematologic safety profiles of tedizolid vs linezolid. We also described nonhematological adverse drug events (ADEs) and therapy discontinuation rates. In an exploratory analysis, we assessed symptomatic microbiologic and clinical outcomes in those receiving tedizolid or linezolid for at least 4 weeks.

Results

Twenty-four patients were included (15 tedizolid, 9 linezolid). No differences were identified comparing the effects of tedizolid vs linezolid on platelet counts, absolute neutrophil counts (ANCs), and hemoglobin over 7 weeks using mixed-effects analysis of variance models. ANC was significantly decreased in both groups after 7 weeks of therapy (P = .04). Approximately 20% of patients in each arm discontinued therapy due to an ADE. Seven of 12 (58%) and 2 of 3 (67%) patients were cured or clinically cured with tedizolid- and linezolid-containing regimens, respectively.

Conclusions

This study suggests no significant safety benefit of tedizolid over linezolid for the treatment of NTM infections in SOT recipients. Tedizolid or linezolid-containing regimens demonstrated a potential benefit in symptomatic and microbiologic improvement. Larger cohorts are needed to further delineate the comparative role of linezolid and tedizolid for the treatment of NTM infections in SOT recipients.

Outcomes of Inhaled Amikacin-Containing Multidrug Regimens for Mycobacterium abscessus Pulmonary Disease

BACKGROUND

Mycobacterium abscessus pulmonary disease (M abscessus-PD) is challenging to treat because of its resistance to antibiotics.

RESEARCH QUESTION

What are the outcomes of treatment-naive patients with M abscessus-PD treated with inhaled amikacin-containing multidrug regimens?

STUDY DESIGN AND METHODS

We identified 82 treatment-naive patients with M abscessus-PD from a prospective observational cohort treated with regimens containing inhaled amikacin with or without clofazimine between March 2015 and June 2018 (ClinicalTrials.gov identifier: NCT00970801). During the initial phase, all patients received IV amikacin, imipenem (or cefoxitin), and oral azithromycin. Oral clofazimine was added in cases of (1) M abscessus subspecies abscessus (here M abscessus) or (2) M abscessus subspecies massiliense (here M massiliense) with cavitary lesions. During the continuation phase, amikacin was changed from an injectional to inhalational form.

RESULTS

Of 82 patients, 46 (56%) had M massiliense-PD and 36 (44%) had M abscessus-PD. Among 59 patients with nodular bronchiectatic disease (72%), 23 of 59 had a concurrent cavitary lesion. The remaining 23 patients (28%) had fibrocavitary disease. Twelve months after treatment initiation, cure was achieved in 53 patients (65%): 42 of 46 patients (91%) with M massiliense-PD and 11 of 36 patients (31%) with M abscessus-PD (P < .001). Symptomatic and radiologic improvements were observed in 72 patients (88%) and 64 patients (78%), respectively, with significantly greater improvement in patients with M massiliense-PD (symptom improvement, 96% vs 78% [P = .047]; improvement on CT scanning, 93% vs 61% [P = .002]).

INTERPRETATION

Inhaled amikacin with or without clofazimine in the regimen provides favorable treatment outcomes in M massiliense-PD. However, more effective treatments are needed for M abscessus-PD.

Efficacy estimation of a combination of triple antimicrobial agents against clinical isolates of Mycobacterium abscessus subsp. abscessus in vitro

Background

Mycobacterium abscessus subsp. abscessus (M. abscessus) is a rapidly growing mycobacterium that is resistant to most antibiotics. The number of patients with pulmonary disease caused by M. abscessus is increasing in several regions, and therapy involves long-term antibiotic combination treatments, although no standard treatment regimen has been established.

Objectives

To examine candidate regimens for maintenance of antimicrobial treatment against M. abscessus by measuring MIC using the three-drug chequerboard method.

Methods

We evaluated the drug susceptibility of 70 clinical isolates of M. abscessus using the three-drug chequerboard method. We tested the antimycobacterial agents bedaquiline, clofazimine, amikacin, and sitafloxacin (which showed a relatively low MIC range when used as single agents) alone and in combinations.

Results

The three-drug combinations of bedaquiline/clofazimine/amikacin, and bedaquiline/clofazimine/sitafloxacin were studied. Among isolates for which the fractional inhibitory concentration index (FICI) could be calculated, 29/70 isolates (41%) and 11/70 isolates (16%) showed a synergistic response (FICI ≤0.75) with combined use of bedaquiline/clofazimine/amikacin, or with bedaquiline/clofazimine/sitafloxacin, respectively.

Conclusions

The combination of bedaquiline with clofazimine plus either amikacin or sitafloxacin may be useful as maintenance regimens when treating pulmonary disease caused by M. abscessus.

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.

Safety and Tolerability of Clofazimine in a Cohort of Children With Odontogenic Mycobacterium abscessus Infection

Mycobacterium abscessus infections can be challenging to treat. Clofazimine has excellent in vitro activity against M abscessus, but reports of its use, particularly in children, have been limited. In this study, clofazimine was given to 27 children during an outbreak of odontogenic mycobacterial infections and seemed to be well tolerated as part of a multidrug regimen.

Alternative and Experimental Therapies of Mycobacterium abscessus Infections

Mycobacterium abscessus is a non-tuberculous mycobacterium notoriously known for causing severe, chronic infections. Treatment of these infections is challenging due to either intrinsic or acquired resistance of M. abscessus to multiple antibiotics. Despite prolonged poly-antimicrobial therapy, treatment of M. abscessus infections often fails, leading to progressive morbidity and eventual mortality. Great research efforts are invested in finding new therapeutic options for M. abscessus. Clofazimine and rifabutin are known anti-mycobacterial antibiotics, repurposed for use against M. abscessus. Novel antimicrobials active against M. abscessus include delamanid, pretomanid and PIPD1 and the recently approved beta-lactamase inhibitors avibactam, relebactam and vaborbactam. Previously unused antimicrobial combinations, e.g. vancomycin–clarithromycin and dual beta-lactam therapy, have been shown to have synergistic effect against M. abscessus in experimental models, suggesting their possible use in multiple-drug regimens. Finally, engineered phage therapy has been reported to be clinically successful in a severe case of disseminated M. abscessus infection. While many of these experimental therapeutics have shown activity against M. abscessus in vitro, as well as in intracellular and/or animal models, most have little if any evidence of effect in human infections. Clinical studies of M. abscesssus treatments are needed to reliably determine the value of their incorporation in therapeutic regimens.

Outcomes of Inhaled Amikacin and Clofazimine-Containing Regimens for Treatment of Refractory Mycobacterium avium Complex Pulmonary Disease

Limited data are available regarding optimal treatment for refractory Mycobacterium avium complex-pulmonary disease (MAC-PD). We evaluated outcomes of inhaled amikacin (AMK) with clofazimine (CFZ) regimens as an add-on salvage therapy for refractory MAC-PD. We retrospectively analyzed 52 patients with refractory MAC-PD, characterized by persistently positive sputum cultures despite >6 months of treatment. Thirty-five (67%) patients had M. intracellulare-PD, and 17 (33%) patients had M. avium-PD. Twenty-seven (52%) patients received the salvage therapy for ≥12 months, whereas 25 (48%) patients were treated for <12 months due to adverse effects or other reasons. Seventeen (33%) patients had culture conversion: 10 (10/27) in the ≥12-month treatment group and seven (7/25) in the <12-month treatment group (p = 0.488). Microbiological cure, defined as maintenance of culture negativity, was achieved in 12 (23%) patients; six (6/12) with accompanying symptomatic improvement were considered to have reached cure. Clinical cure, defined as symptomatic improvement with <3 consecutive negative cultures, was achieved in three (6%) patients. Overall, 15 (29%) patients achieved favorable outcomes, including microbiological cure, cure, and clinical cure. Inhaled AMK with CFZ may provide favorable outcomes in some patients with refractory MAC-PD. However, given the adverse effects, more effective strategies are needed to maintain these therapeutic regimens.

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.

False-positive blood cultures: The need for follow-up

The diagnosis of blood-borne infections in immunocompromised patients is a major challenge for the clinical microbiology laboratory. Isolation of bloodborne pathogens in these patients has profound clinical implications, yet is fraught with technical problems, including the presence of unusual and difficult to isolate pathogens. Coupled with this is the problem of false-positive blood culture signals from automated blood culture systems which further delays the definitive diagnosis. Here, we present a case of an 8-year-old boy with Ph +ve acute lymphoblastic leukaemia who has repeated 'false positive' blood cultures and later grew an uncommon organism.

Treatment for Mycobacterium abscessus complex-lung disease

Nontuberculous mycobacterial infections and colonization are becoming more prevalent worldwide. Mycobacterium abscessus complex (MABC) is one of the predominant pathogens capable of a wide spectrum of infections, with 50% of infections involving the lungs. The decision to commence treatment is determined according to the severity of the disease, risk of progressive disease, presence of comorbidities, and goals of treatment. MABC is resistant to standard antituberculous agents and has variable drug susceptibility across different geographical locations, therefore, antibiotic susceptibility testing of all clinically significant isolates is crucial for selecting a treatment strategy. Pulmonary infections due to MABC is difficult to cure using the currently recommended regimens from the American Thoracic Society and British Thoracic Society. Macrolides are the cornerstone of treatment, but the efficacy of macrolide-based chemotherapy may be compromised by resistance. Despite the introduction of new drugs for treatment, treatment outcomes remain unsatisfactory. The combination of surgical resection of limited lung disease regions with a multidrug, macrolide-based therapy offers the optimal chance of achieving clinical cure of the disease. This review focuses on medical treatment of MABC-lung disease and the efficacy of new agents, such as clofazimine, amikacin inhalation therapy, tigecycline and linezolid, for treating MABC-lung disease.

Clofazimine: an old drug for never-ending diseases

Clofazimine (CFZ), an old hydrophobic riminophenazine, has a wide range of antimycobacterial activity ranging from leprosy to nontuberculous mycobacterial diseases. CFZ has several advantages such as a favorable pharmacokinetic profile, dose-dependent side effects as well as low price. In this narrative review, we have assessed the clinical development of CFZ, starting from the potential in vitro mechanism of actions, to the spectrum of side effects and potential drug-drug interactions, highlighting its current place in therapy and future possible use in leprosy, nontuberculous mycobacterial diseases and drug-resistant tuberculosis.

State-of-the-art treatment strategies for nontuberculous mycobacteria infections

INTRODUCTION

Non-tuberculous Mycobacteria (NTM) are a group of organisms whose importance in medicine seems to be increasing in recent times. The increasing number of patients susceptible to these diseases make it necessary to expand our knowledge of therapeutic options and to explore future possibilities for the development of a therapeutic arsenal.

AREAS COVERED

In this review, the authors provide a brief introduction about the present importance of NTM and describe the present recommendations of the available guidelines for their treatment. They include a description of the future options for the management of these patients, especially focusing on new antibiotics. The authors also look at possibilities for future therapeutic options, such as antibiofilm strategies.

EXPERT OPINION

No actual changes have been made to the current recommendations for the management of most NTM infections (except perhaps the availability of nebulized amikacin). However, it is also true that we have increased the number of available antibiotic treatment options with good in vitro activity against NTM. The use of these drugs in selected cases could increase the therapeutic possibilities. However, some problems are still present, such as the knowledge of the actual meaning of a NTM isolate, and will probably be a key part of future research.

Clofazimine in Mycobacterium abscessus peritonitis: A pediatric case report

Peritonitis- and catheter-related infections due to nontuberculous mycobacteria (NTM) including Mycobacterium abscessus have been reported among adults on peritoneal dialysis (PD). There is no recommended antimicrobial regimen for the treatment of M. abscessus peritonitis. Clofazimine has emerged as an important adjuvant antimicrobial treatment of M. abscessus lung infection. We report, to our knowledge, the first case of M. abscessus PD peritonitis in a child treated successfully using clofazimine as a novel adjuvant therapy to amikacin and clarithromycin. Her clinical features were similar to those of bacterial peritonitis, but she had persistence of symptoms and high inflammatory markers despite empirical therapy for peritonitis. Bacterial culture of PD effluent became positive for M. abscessus after 5 days. There was complete symptom resolution after 6 days of multidrug therapy. Due to ototoxicity, amikacin was discontinued after 6 weeks, while clarithromycin and clofazimine were continued for 9 months to ensure complete pathogen eradication before a planned renal transplant. A high index of suspicion in refractory or culture-negative cases is important for the diagnosis of NTM peritonitis. Multidrug therapy is recommended for M. abscessus infections. Clofazimine was chosen as a novel adjunct antimicrobial because of its pharmacokinetics, ease of administration, cost-effectiveness, and lack of serious adverse events.

Assessment of Clofazimine and TB47 Combination Activity against Mycobacterium abscessus Using a Bioluminescent Approach

Mycobacterium abscessus is intrinsically resistant to most antimicrobial agents. The emerging infections caused by M. abscessus and the lack of effective treatment call for rapid attention. Here, we intended to construct a selectable marker-free autoluminescent M. abscessus strain (designated UAlMab) as a real-time reporter strain to facilitate the discovery of effective drugs and regimens for treating M. abscessus The UAlMab strain was constructed using the dif/Xer recombinase system. In vitro and in vivo activities of several drugs, including clofazimine and TB47, a recently reported cytochrome bc ₁ inhibitor, were assessed using UAlMab. Furthermore, the efficacy of multiple drug combinations, including the clofazimine and TB47 combination, were tested against 20 clinical M. abscessus isolates. The UAlMab strain enabled us to evaluate drug efficacy both in vitro and in live BALB/c mice in a real-time, noninvasive fashion. Importantly, although TB47 showed marginal activity either alone or in combination with clarithromycin, amikacin, or roxithromycin, the drug markedly potentiated the activity of clofazimine, both in vitro and in vivo This study demonstrates that the use of the UAlMab strain can significantly facilitate rapid evaluation of new drugs and regimens. The clofazimine and TB47 combination is effective against M. abscessus, and dual/triple electron transport chain (ETC) targeting can be an effective therapeutic approach for treating mycobacterial infections.

Non-tuberculous mycobacteria and the rise of Mycobacterium abscessus

Infections caused by non-tuberculous mycobacteria (NTM) are increasing globally and are notoriously difficult to treat due to intrinsic resistance of these bacteria to many common antibiotics. NTM are diverse and ubiquitous in the environment, with only a few species causing serious and often opportunistic infections in humans, including Mycobacterium abscessus. This rapidly growing mycobacterium is one of the most commonly identified NTM species responsible for severe respiratory, skin and mucosal infections in humans. It is often regarded as one of the most antibiotic-resistant mycobacteria, leaving us with few therapeutic options. In this Review, we cover the proposed infection process of M. abscessus, its virulence factors and host interactions and highlight the commonalities and differences of M. abscessus with other NTM species. Finally, we discuss drug resistance mechanisms and future therapeutic options. Taken together, this knowledge is essential to further our understanding of this overlooked and neglected global threat.

Looking beyond Typical Treatments for Atypical Mycobacteria

The genus Mycobacterium comprises not only the deadliest of bacterial pathogens, Mycobacterium tuberculosis, but several other pathogenic species, including M. avium and M. abscessus. The incidence of infections caused by atypical or nontuberculous mycobacteria (NTM) has been steadily increasing, and is associated with a panoply of diseases, including pulmonary, soft-tissue, or disseminated infections. The treatment for NTM disease is particularly challenging, due to its long duration, to variability in bacterial susceptibility profiles, and to the lack of evidence-based guidelines. Treatment usually consists of a combination of at least three drugs taken from months to years, often leading to severe secondary effects and a high chance of relapse. Therefore, new treatment approaches are clearly needed. In this review, we identify the main limitations of current treatments and discuss different alternatives that have been put forward in recent years, with an emphasis on less conventional therapeutics, such as antimicrobial peptides, bacteriophages, iron chelators, or host-directed therapies. We also review new forms of the use of old drugs, including the repurposing of non-antibacterial molecules and the incorporation of antimicrobials into ionic liquids. We aim to stimulate advancements in testing these therapies in relevant models, in order to provide clinicians and patients with useful new tools with which to treat these devastating diseases.

Medical management of atraumatic Mycobacterium abscessus cutaneous infection: A case report

Treatment for cutaneous infection from Mycobacterium abscessus is fraught with poorly established evidence. Given its antibiotic multi-resistance, surgical intervention is often recommended. We report a case of cutaneous M. abscessus infection that was successfully managed with medical therapy alone. A 55-year-old immunocompetent woman from the Bellarine peninsula in Victoria, Australia presented to our hospital with a 2-week history of a non-healing ulcer on her left forearm. The patient had no history of trauma or procedures to the skin. On presentation, the patient had a punch biopsy, which was culture positive for M. abscessus. The isolate was susceptible to clarithromycin and amikacin, had intermediate susceptibility to ciprofloxacin, cefoxitin and linezolid and was resistant to doxycycline, imipenem, cotrimoxazole and moxifloxacin. The tigecycline MIC was 0.25 μg/ml. The patient received a total of 12 weeks of oral clarithromycin 500 mg twice daily, 4 weeks of intravenous amikacin 500 mg daily, 6 weeks of intravenous tigecycline 100 mg over 24 hours via Baxter pump, and 4 weeks of oral clofazimine 100 mg daily. The patient made a good clinical recovery and had her medical therapy ceased after 12 weeks. M. abscessus cutaneous infection in an immunocompetent individual without antecedent trauma or surgery is rare. Our case illustrates the successful treatment of a deep M. abscessus cutaneous ulcer with relatively short duration macrolide-based antibiotic therapy without any surgical intervention.

Prognostic factors associated with long-term mortality in 1445 patients with nontuberculous mycobacterial pulmonary disease: a 15-year follow-up study

Limited data are available regarding the prognostic factors for patients with nontuberculous mycobacterial pulmonary disease (NTM-PD). We investigated the prognostic factors associated with long-term mortality in NTM-PD patients after adjusting for individual confounders, including aetiological organism and radiological form.

A total of 1445 patients with treatment-naïve NTM-PD who were newly diagnosed between July 1997 and December 2013 were included. The aetiological organisms were as follows: Mycobacterium avium (n=655), M. intracellulare (n=487), M. abscessus (n=129) and M. massiliense (n=174). The factors associated with mortality in NTM-PD patients were analysed using a multivariable Cox model after adjusting for demographic, radiological and aetiological data.

The overall 5-, 10- and 15-year cumulative mortality rates for the NTM-PD patients were 12.4%, 24.0% and 36.4%, respectively. On multivariable analysis, the following factors were significantly associated with mortality in NTM-PD patients: old age, male sex, low body mass index, chronic pulmonary aspergillosis, pulmonary or extrapulmonary malignancy, chronic heart or liver disease and erythrocyte sedimentation rate. The aetiological organism was also significantly associated with mortality: M. intracellulare had an adjusted hazard ratio (aHR) of 1.40, 95% CI 1.03–1.91; M. abscessus had an aHR of 2.19, 95% CI 1.36–3.51; and M. massiliense had an aHR of 0.99, 95% CI 0.61–1.64, compared to M. avium. Mortality was also significantly associated with the radiological form of NTM-PD for the cavitary nodular bronchiectatic form (aHR 1.70, 95% CI 1.12–2.59) and the fibrocavitary form (aHR 2.12, 95% CI 1.57–3.08), compared to the non-cavitary nodular bronchiectatic form.

Long-term mortality in patients with NTM-PD was significantly associated with the aetiological NTM organism, cavitary disease and certain demographic characteristics.

Recent advances in nontuberculous mycobacterial lung infections

Nontuberculous mycobacteria (NTM) are members of the Mycobacterium genus other than Mycobacterium tuberculosis complex and Mycobacterium leprae. NTM are widely distributed in the environment and are increasingly recognized as causes of chronic lung disease that can be challenging to treat. In this brief review, we consider recent developments in the ecology, epidemiology, natural history, and treatment of NTM lung disease with a focus on Mycobacterium avium complex (MAC) and Mycobacterium abscessus complex .

Pharmacotherapy Approaches in Nontuberculous Mycobacteria Infections

Nontuberculous mycobacteria (NTM) comprise a heterogeneous group of organisms, with only a small subset known to cause disease in humans. Although NTM infection is not a reportable disease, both the increasing clinical recognition and recent advancements in laboratory diagnostic capabilities of NTM infections in immunocompromised and immunocompetent patients are rapidly evolving. We reviewed antimicrobial agents used to treat the most frequently encountered NTM infections and examined optimized drug dosing strategies, toxicity profiles, drug-drug interactions, and the role of therapeutic drug monitoring. Antimicrobial susceptibility testing and patient monitoring on therapy were also examined. We used PubMed to review the published literature on the management of select NTM pathogens, the common syndromes encountered since 2000, and select pharmacokinetic principles of select antimicrobial agents used since 1990. We included select clinical trials, systematic reviews, published guidelines, and observational studies when applicable. The prolonged duration and the necessity for combination therapy for most forms of NTM disease can be problematic for many patients. A multidisciplinary care team that includes pharmacy engagement may help increase rates of optimal patient tolerability and successful treatment completion.

Non-tuberculous mycobacterial pulmonary disease

Nontuberculous mycobacterial pulmonary disease (NTM-PD) is a challenging infection which is becoming increasingly prevalent, particularly in the elderly, for reasons which are unknown. While underlying lung disease is a well-established risk factor for NTM-PD, it may also occur in apparently healthy individuals. No single common genetic or immunological defect has been identified in this group, and it is likely that multiple pathways contribute towards host susceptibility to NTM-PD which further interact with environmental and microbiological factors leading to the development of disease.The diagnosis of NTM-PD relies on the integration of clinical, radiological and microbiological results. The clinical course of NTM-PD is heterogeneous, with some patients remaining stable without the need for treatment and others developing refractory disease associated with considerable mortality and morbidity. Treatment regimens are based on the identity of the isolated species, drug sensitivity testing (for some agents) and the severity of disease. Multiple antibiotics are typically required for prolonged periods of time and treatment is frequently poorly tolerated. Surgery may be beneficial in selected cases. In some circumstances cure may not be attainable and there is a pressing need for better regimens to treat refractory and drug-resistant NTM-PD.This review summarises current knowledge on the epidemiology, aetiology and diagnosis of NTM-PD and discusses the treatment of two of the most clinically significant species, the M. avium and M. abscessus complexes, with a focus on refractory disease and novel therapies.

Outcomes in Lung Transplant Recipients With Mycobacterium abscessus Infection: A 15-Year Experience From a Large Tertiary Care Center

BACKGROUND

Mycobacterium abscessus (M abscessus) infection is a serious complication post-lung transplant (LTx). We examined determinants of outcomes in LTx recipients infected with M abscessus.

METHODS

Electronic records of all patients who underwent LTx in a single transplant center between 2000 and 2015 were screened for isolation of M abscessus before or after LTx.

RESULTS

Twenty-six cases of M abscessus isolation were identified. Twenty-four had M abscessus isolation post-LTx. Two had M abscessus isolated from a surgical site, while the others were pulmonary isolates. Out of these 22 with pulmonary isolates, 12 had clinical disease. In 73% of patients, treatment had to be temporarily held or switched due to intolerance and toxicity. There was a statistically significant worsening in survival in those who developed clinical disease compared to matched controls. Among the 12 patients with clinical pulmonary disease, use of clofazimine was significantly associated with a favorable outcome. Six patients had M abscessus isolation pretransplant. Four developed M abscessus recurrence at a median of 2 months post-LTx. Two recurrences were surgical site infections, and 2 were pulmonary infections.

CONCLUSION

M abscessus infection is difficult to treat as tolerance to medications used is poor. M abscessus pneumonia is associated with worse survival post-LTx. Use of clofazimine is associated with 1-year infection-free survival.