Nontuberculous Mycobacteria in Cystic Fibrosis

Altered serine metabolism promotes drug tolerance in Mycobacterium abscessus via a WhiB7-mediated adaptive stress response

Mycobacterium abscessus is an emerging opportunistic pathogen responsible for chronic lung diseases, especially in patients with cystic fibrosis. Treatment failure of M. abscessus infections is primarily associated with intrinsic or acquired antibiotic resistance. However, there is growing evidence that antibiotic tolerance, i.e., the ability of bacteria to transiently survive exposure to bactericidal antibiotics through physiological adaptations, contributes to the relapse of chronic infections and the emergence of acquired drug resistance. Yet, our understanding of the molecular mechanisms that underlie antibiotic tolerance in M. abscessus remains limited. In the present work, a mutant with increased cross-tolerance to the first- and second-line antibiotics cefoxitin and moxifloxacin, respectively, has been isolated by experimental evolution. This mutant harbors a mutation in serB2, a gene involved in L-serine biosynthesis. Metabolic changes caused by this mutation alter the intracellular redox balance to a more reduced state that induces overexpression of the transcriptional regulator WhiB7 during the stationary phase, promoting tolerance through activation of a WhiB7-dependant adaptive stress response. These findings suggest that alteration of amino acid metabolism and, more generally, conditions that trigger whiB7 overexpression, makes M. abscessus more tolerant to antibiotic treatment.

Treatable traits and challenges in the clinical management of non-tuberculous mycobacteria lung disease in people with cystic fibrosis

INTRODUCTION

Over the last ten years an increasing prevalence and incidence of non-tuberculous mycobacteria (NTM) has been reported among patients with cystic fibrosis (CF) Viviani (J Cyst Fibros, 15(5):619-623, 2016). NTM pulmonary disease has been associated with negative clinical outcomes and often requires pharmacological treatment. Although specific guidelines help clinicians in the process of diagnosis and clinical management, the focus on the multidimensional assessment of concomitant problems is still scarce.

MAIN BODY

This review aims to identify the treatable traits of NTM pulmonary disease in people with CF and discuss the importance of a multidisciplinary approach in order to detect and manage all the clinical and behavioral aspects of the disease. The multidisciplinary complexity of NTM pulmonary disease in CF requires careful management of respiratory and extra-respiratory, including control of comorbidities, drug interactions and behavioral factors as adherence to therapies.

CONCLUSIONS

The treatable trait strategy can help to optimize clinical management through systematic assessment of all the aspects of the disease, providing a holistic treatment for such a multi-systemic and complex condition.

Culture, Identification, and Antimicrobial Susceptibility Testing of Pulmonary Nontuberculous Mycobacteria

Nontuberculous mycobacteria (NTM) typically cause opportunistic pulmonary infections and reliable laboratory results can assist with diagnosis of disease. Microscopy can detect acid-fast bacilli from specimens though it has poor sensitivity. Solid and liquid culture are used to grow NTM, which are identified by molecular or protein-based assays. Because culture has a long turnaround time, some assays are designed to identify NTM directly from sputum specimens. When indicated, phenotypic susceptibility testing should be performed by broth microdilution as per the guidelines from the Clinical Laboratory Standards Institute. Genotypic susceptibility methods may be used to decrease the turnaround time for some antimicrobials.

Reduced Sphingosine in Cystic Fibrosis Increases Susceptibility to Mycobacterium abscessus Infections

Cystic fibrosis (CF) is an autosomal recessive disorder caused by the deficiency of the cystic fibrosis transmembrane conductance regulator (CFTR) and often leads to pulmonary infections caused by various pathogens, including Staphylococcus aureus, Pseudomonas aeruginosa, and nontuberculous mycobacteria, particularly Mycobacterium abscessus. Unfortunately, M. abscessus infections are increasing in prevalence and are associated with the rapid deterioration of CF patients. The treatment options for M. abscessus infections are limited, requiring the urgent need to comprehend infectious pathogenesis and develop new therapeutic interventions targeting affected CF patients. Here, we show that the deficiency of CFTR reduces sphingosine levels in bronchial and alveolar epithelial cells and macrophages from CF mice and humans. Decreased sphingosine contributes to the susceptibility of CF tissues to M. abscessus infection, resulting in a higher incidence of infections in CF mice. Notably, treatment of M. abscessus with sphingosine demonstrated potent bactericidal activity against the pathogen. Most importantly, restoration of sphingosine levels in CF cells, whether human or mouse, and in the lungs of CF mice, provided protection against M. abscessus infections. Our findings demonstrate that pulmonary sphingosine levels are important in controlling M. abscessus infection. These results offer a promising therapeutic avenue for CF patients with pulmonary M. abscessus infections.

Pulmonary bacteriophage and cystic fibrosis airway mucus: friends or foes?

For those born with cystic fibrosis (CF), hyper-concentrated mucus with a dysfunctional structure significantly impacts CF airways, providing a perfect environment for bacterial colonization and subsequent chronic infection. Early treatment with antibiotics limits the prevalence of bacterial pathogens but permanently alters the CF airway microenvironment, resulting in antibiotic resistance and other long-term consequences. With little investment into new traditional antibiotics, safe and effective alternative therapeutic options are urgently needed. One gathering significant traction is bacteriophage (phage) therapy. However, little is known about which phages are effective for respiratory infections, the dynamics involved between phage(s) and the host airway, and associated by-products, including mucus. Work utilizing gut cell models suggest that phages adhere to mucus components, reducing microbial colonization and providing non-host-derived immune protection. Thus, phages retained in the CF mucus layer result from the positive selection that enables them to remain in the mucus layer. Phages bind weakly to mucus components, slowing down the diffusion motion and increasing their chance of encountering bacterial species for subsequent infection. Adherence of phage to mucus could also facilitate phage enrichment and persistence within the microenvironment, resulting in a potent phage phenotype or vice versa. However, how the CF microenvironment responds to phage and impacts phage functionality remains unknown. This review discusses CF associated lung diseases, the impact of CF mucus, and chronic bacterial infection. It then discusses the therapeutic potential of phages, their dynamic relationship with mucus and whether this may enhance or hinder airway bacterial infections in CF.

Microbiological profile, preclinical pharmacokinetics and efficacy of CRS0393, a novel antimycobacterial agent targeting MmpL3

The benzothiazole amide CRS0393 demonstrated excellent in vitro activity against nontuberculous mycobacteria (NTM), including M. abscessus isolates from cystic fibrosis (CF) patients, with minimum inhibitory concentrations (MICs) of ≤0.03-0.5 μg/mL. The essential transport protein MmpL3 was confirmed as the target via analysis of spontaneous resistant mutants and further biological profiling. In mouse pharmacokinetic studies, intratracheal instillation of a single dose of CRS0393 resulted in high concentrations of drug in epithelial lining fluid (ELF) and lung tissue, which remained above the M. abscessus MIC for at least 9 hours post-dose. This exposure resulted in a penetration ratio of 261 for ELF and 54 for lung tissue relative to plasma. CRS0393 showed good oral bioavailability, particularly when formulated in kolliphor oil, with a lung-to-plasma penetration ratio ranging from 0.5 to 4. CRS0393 demonstrated concentration-dependent reduction of intracellular M. abscessus in a THP-1 macrophage infection model. CRS0393 was well tolerated following intranasal administration (8 mg/kg) or oral dosing (25 mg/kg) once daily for 28 days in dexamethasone-treated C3HeB/FeJ mice. Efficacy against M. abscessus strain 103 was achieved via the intranasal route, while oral dosing will need further optimization. CRS0393 holds promise for development as a novel agent with broad antimycobacterial activity.

Opportunistic etiological agents causing lung infections: emerging need to transform lung-targeted delivery

Lung diseases continue to draw considerable attention from biomedical and public health care agencies. The lung with the largest epithelial surface area is continuously exposed to the external environment during exchanging gas. Therefore, the chances of respiratory disorders and lung infections are overgrowing. This review has covered promising and opportunistic etiologic agents responsible for lung infections. These pathogens infect the lungs either directly or indirectly. However, it is difficult to intervene in lung diseases using available oral or parenteral antimicrobial formulations. Many pieces of research have been done in the last two decades to improve inhalable antimicrobial formulations. However, very few have been approved for human use. This review article discusses the approved inhalable antimicrobial agents (AMAs) and identifies why pulmonary delivery is explored. Additionally, the basic anatomy of the respiratory system linked with barriers to AMA delivery has been discussed here. This review opens several new scopes for researchers to work on pulmonary medicines for specific diseases and bring more respiratory medication to market.

Biofilm infection of a central venous port-catheter caused by Mycobacterium avium complex in an immunocompetent child with cystic fibrosis

BACKGROUND

Mycobacterium (M.) chimaera is a non-tuberculous mycobacterium (NTM) that belongs to M. avium complex (MAC). In patients with cystic fibrosis (CF), MAC can cause bronchopulmonary infections that can be prolonged and difficult to treat. MAC infections of sites other than the lungs or central catheters are rare and almost exclusively associated with immunodeficiency.

CASE PRESENTATION

We present a case of an 8-year-old CF patient (delF508 homozygous) with recurrent pulmonary exacerbations, gradual clinical deterioration, B-symptoms (fever, fatigue, weight loss, night sweat), elevated transaminases and intermittent detection of M. chimaera in the sputum without radiological signs of NTM-associated lung disease with a central venous port-catheter. Next-generation sequencing (NGS) revealed M. chimaera port infection that was also confirmed by mycobacterial culture. The patient recovered within 4 weeks after removal of the catheter and initiation of MAC targeted antimicrobial therapy. Electron microscopy of the catheter illustrated the presence of mycobacteria in a biofilm.

CONCLUSIONS

MAC central venous catheter infection needs to be considered in immunocompetent people. NGS is a valuable tool for rapid identification of rare infections. MAC capability of biofilm formation renders catheter removal the central therapeutic intervention for the clearance of the infection.

Challenges and opportunities in the development of novel antimicrobial therapeutics for cystic fibrosis

Chronic respiratory infection is the primary driver of mortality in individuals with cystic fibrosis (CF). Existing drug screening models utilised in preclinical antimicrobial development are unable to mimic the complex CF respiratory environment. Consequently, antimicrobials showing promising activity in preclinical models often fail to translate through to clinical efficacy in people with CF. Model systems used in CF anti-infective drug discovery and development range from antimicrobial susceptibility testing in nutrient broth, through to 2D and 3D in vitro tissue culture systems and in vivo models. No single model fully recapitulates every key aspect of the CF lung. To improve the outcomes of people with CF (PwCF) it is necessary to develop a set of preclinical models that collectively recapitulate the CF respiratory environment to a high degree of accuracy. Models must be validated for their ability to mimic aspects of the CF lung and associated lung infection, through evaluation of biomarkers that can also be assessed following treatment in the clinic. This will give preclinical models greater predictive power for identification of antimicrobials with clinical efficacy. The landscape of CF is changing, with the advent of modulator therapies that correct the function of the CFTR protein, while antivirulence drugs and phage therapy are emerging alternative treatments to chronic infection. This review discusses the challenges faced in current antimicrobial development pipelines, including the advantages and disadvantages of current preclinical models and the impact of emerging treatments.

Modulating macrophage function to reinforce host innate resistance against Mycobacterium avium complex infection

Mycobacterium avium complex (MAC) is the main causative agent of infectious diseases in humans among nontuberculous mycobacteria (NTM) that are ubiquitous organisms found in environmental media such as soil as well as in domestic and natural waters. MAC is a primary causative agent of NTM-lung disease that threaten immunocompromised or structural lung disease patients. The incidence and the prevalence of M. tuberculosis infection have been reduced, while MAC infections and mortality rates have increased, making it a cause of global health concern. The emergence of drug resistance and the side effects of long-term drug use have led to a poor outcome of treatment regimens against MAC infections. Therefore, the development of host-directed therapy (HDT) has recently gained interest, aiming to accelerate mycobacterial clearance and reversing lung damage by employing the immune system using a novel adjuvant strategy to improve the clinical outcome of MAC infection. Therefore, in this review, we discuss the innate immune responses that contribute to MAC infection focusing on macrophages, chief innate immune cells, and host susceptibility factors in patients. We also discuss potential HDTs that can act on the signaling pathway of macrophages, thereby contributing to antimycobacterial activity as a part of the innate immune response during MAC infection. Furthermore, this review provides new insights into MAC infection control that modulates and enhances macrophage function, promoting host antimicrobial activity in response to potential HDTs and thus presenting a deeper understanding of the interactions between macrophages and MACs during infection.

Physiologically Based Pharmacokinetic Modeling To Guide Management of Drug Interactions between Elexacaftor-Tezacaftor-Ivacaftor and Antibiotics for the Treatment of Nontuberculous Mycobacteria

Nontuberculous mycobacteria (NTM) are the pathogens of concern in people with cystic fibrosis (pwCF) due to their association with deterioration of lung function. Treatment requires the use of a multidrug combination regimen, creating the potential for drug-drug interactions (DDIs) with cystic fibrosis transmembrane conductance regulator (CFTR)-modulating therapies, including elexacaftor, tezacaftor, and ivacaftor (ETI), which are eliminated mainly through cytochrome P450 (CYP) 3A-mediated metabolism. An assessment of the DDI risk for ETI coadministered with NTM treatments, including rifabutin, clofazimine, and clarithromycin, is needed to provide appropriate guidance on dosing.

Viruses to the rescue-Use of bacteriophage to treat resistant pulmonary infections

People with cystic fibrosis (CF) are commonly infected with difficult to treat organisms, including non-tuberculous mycobacteria. Bacteriophage are viruses that lyse specific bacteria. Nick and colleagues describe the first successful treatment of a Mycobacterium abscessus lung infection with bacteriophage in an immune competent individual. This report provides important information regarding the efficacy of phage therapy and timeline of treatment response.

Tissue-localized immune responses in people with cystic fibrosis and respiratory nontuberculous mycobacteria infection

Nontuberculous mycobacteria (NTM) are an increasingly common cause of respiratory infection in people with cystic fibrosis (PwCF). Relative to those with no history of NTM infection (CF-NTMNEG), PwCF and a history of NTM infection (CF-NTMPOS) are more likely to develop severe lung disease and experience complications over the course of treatment. In other mycobacterial infections (e.g. tuberculosis), an overexuberant immune response causes pathology and compromises organ function; however, since the immune profiles of CF-NTMPOS and CF-NTMNEG airways are largely unexplored, it is unknown which if any immune responses distinguish these cohorts or concentrate in damaged tissues. Here we evaluated lung lobe-specific immune profiles of three cohorts (CF-NTMPOS, CF-NTMNEG, and non-CF adults) and found that CF-NTMPOS airways are distinguished by a hyper-inflammatory cytokine profile. Importantly, the CF-NTMPOS airway immune profile was dominated by B cells, classical macrophages and the cytokines which support their accumulation. These and other immunological differences between cohorts, including the near absence of NK cells and complement pathway members, were enriched in the most damaged lung lobes. The implications of these findings for our understanding of lung disease in PwCF are discussed, as are how they may inform the development of host-directed therapies to improve NTM disease treatment.

Treating nontuberculous mycobacteria in children with cystic fibrosis: a multicentre retrospective study

BACKGROUND

Respiratory infection with nontuberculous mycobacteria (NTM) in children with cystic fibrosis (CF) has increased in prevalence. The condition is difficult to diagnose and treatments are complex with limited evidence to guide practice. This study describes the approaches to diagnosis, management and consequences of treatment in a multicentre cohort of children with CF in the UK.

METHODS

Retrospective data were collected from 11 CF specialist centres from patients less than 17 years old, treated for NTM infection between 2006 and 2017. Descriptive statistics were used to describe the clinical characteristics of children treated. Treatment regimens, adverse events and success of treatment, with respect to lung function and culture conversion, were evaluated.

RESULTS

Data from 70 patients treated for NTM pulmonary disease were collated (60 Mycobacterium abscessus complex (MABSC); 10 M. avium complex (MAC)). Older age and previous diagnosis of allergic bronchopulmonary aspergillosis were all significantly associated with NTM. There was a wide variance in drug choice and side effects were reported with all agents. NTM eradication occurred in 80% of patients with MAC and 48% with MABSC, with variable outcomes on lung function.

CONCLUSIONS

Diagnosis and treatment of NTM infection in children with CF is challenging. Treatment success is not guaranteed, particularly for MABSC. Large clinical trials are urgently required to evaluate treatment regimes and their suitability and efficacy in children.

Genetic Determinants of Tigecycline Resistance in Mycobacteroides abscessus

Mycobacteroides abscessus (formerly Mycobacterium abscessus) is a clinically important, rapid-growing non-tuberculous mycobacterium notoriously known for its multidrug-resistance phenotype. The intrinsic resistance of M. abscessus towards first- and second-generation tetracyclines is mainly due to the over-expression of a tetracycline-degrading enzyme known as MabTetX (MAB_1496c). Tigecycline, a third-generation tetracycline, is a poor substrate for the MabTetX and does not induce the expression of this enzyme. Although tigecycline-resistant strains of M. abscessus have been documented in different parts of the world, their resistance determinants remain largely elusive. Recent work on tigecycline resistance or reduced susceptibility in M. abscessus revealed the involvement of the gene MAB_3508c which encodes the transcriptional activator WhiB7, as well as mutations in the sigH-rshA genes which control heat shock and oxidative-stress responses. The deletion of whiB7 has been observed to cause a 4-fold decrease in the minimum inhibitory concentration of tigecycline. In the absence of environmental stress, the SigH sigma factor (MAB_3543c) interacts with and is inhibited by the anti-sigma factor RshA (MAB_3542c). The disruption of the SigH-RshA interaction resulting from mutations and the subsequent up-regulation of SigH have been hypothesized to lead to tigecycline resistance in M. abscessus. In this review, the evidence for different genetic determinants reported to be linked to tigecycline resistance in M. abscessus was examined and discussed.

Multiresistant organisms: bacteria and beyond

PURPOSE OF REVIEW

Infections with multiresistant organisms are an emerging problem, cause early mortality post lung transplantation and are sometimes associated with graft dysfunction. Frequently they raise questions about the selection of lung transplant candidates and therapeutic management post lung transplantation. There are no guidelines and management must be individualized. This review summarizes the available therapeutic options in cases of multidrug-resistant (MDR) organisms and outcomes after lung transplant.

RECENT FINDINGS

Improvements in diagnosis, new and more effective drugs and the experience gained in the management of these infections in lung transplantation, lead to a more optimistic horizon than that found a decade ago.

SUMMARY

Update on the management of Burkholderia cepacia complex, Mycobacterium abscessus complex, Aspergillus spp., Scedosporium spp. and Lomentospora prolificans infections. This review clarifies current posttransplant outcomes and adds a little hope in these scenarios.

Polycationic Glycopolymer Demonstrates Activity Against Persisters and Biofilms of Non-tuberculosis Mycobacteria Cystic Fibrosis Clinical Isolates in vitro

Non-tuberculosis Mycobacterium (NTM) is a group of opportunistic pathogens associated with pulmonary infections that are difficult to diagnose and treat. Standard treatment typically consists of prolonged combination antibiotic therapy. Antibiotic resistance and the role of biofilms in pathogen communities, such as NTM persister cells, is an important unmet challenge that leads to increased toxicity, frequent relapse, poor clinical management, and an extended treatment period. Infection recurrence and relapse are not uncommon among individuals with cystic fibrosis (CF) or chronic obstructive pulmonary disease (COPD), where thick mucus supports bacterial biofilm production and impairs mucociliary clearance. The study evaluates a membrane-active cationic glycopolymer [poly (acetyl, arginyl) glucosamine (PAAG)] being developed to support the safe and effective treatment of NTM biofilm infections. PAAG shows antibacterial activity against a wide range of pathogenic bacteria at concentrations non-toxic to human epithelial cells. Time-kill curves demonstrated PAAG’s rapid bactericidal potential at concentrations as low as 1X MIC against all NTM strains tested and compared to the standard of care. PAAG treatment prevents persister formation and eradicates antibiotic-induced persister cells in planktonic NTM cultures below the limit of detection (10 colony-forming unit (CFU)/ml). Further, PAAG showed the ability to penetrate and disperse NTM biofilms formed by both rapidly and slowly growing strains, significantly reducing the biofilm biomass (p < 0.0001) compared to the untreated NTM biofilms. Microscopical examination confirmed PAAG’s ability to disrupt and disperse mycobacterial biofilms. A single PAAG treatment resulted in up to a 25-fold reduction in live-labeled NTM and a 78% reduction in biofilm thickness. Similar to other polycationic molecules, PAAG’s bactericidal and antibiofilm activities employ rapid permeabilization of the outer membrane of the NTM strains, and subsequently, reduce the membrane potential even at concentrations as low as 50 μg/ml (p < 0.001). The outcomes of these in vitro analyses suggest the importance of this polycationic glycopolymer, PAAG, as a potential therapeutic agent for opportunistic NTM infections.

Chasing a Breath of Fresh Air in Cystic Fibrosis (CF): Therapeutic Potential of Selective HDAC6 Inhibitors to Tackle Multiple Pathways in CF Pathophysiology

Compelling new support has been provided for histone deacetylase isoform 6 (HDAC6) as a common thread in the generation of the dysregulated proinflammatory and fibrotic phenotype in cystic fibrosis (CF). HDAC6 also plays a crucial role in bacterial clearance or killing as a direct consequence of its effects on CF immune responses. Inhibiting HDAC6 functions thus eventually represents an innovative and effective strategy to tackle multiple aspects of CF-associated lung disease. In this Perspective, we not only showcase the latest evidence linking HDAC(6) activity and expression with CF phenotype but also track the new dawn of HDAC(6) modulators in CF and explore potentialities and future perspectives in the field.

The frequency and related factors of non-tuberculosis mycobacteria infections among patients with cystic fibrosis

BACKGROUND

Non-tuberculous mycobacteria (NTM) can cause chronic lung infection particularly in patients who have structural lung disease such as cystic fibrosis (CF). We evaluated the incidence and management of NTM infections in patients with CF in our center.

METHODS

A retrospective cohort study was carried out on CF patients having at least one positive NTM isolate between 2012 and 2020.

RESULTS

Ten patients (2.1%) had at least one positive NTM culture from respiratory samples. All of them were vaccinated with Bacille Calmette-Guérin (BCG) vaccine, which is in the national vaccination program in our country. Eight patients had the Mycobacterium abscessus complex, one had Mycobacterium avium, and one had Mycobacterium szulgai growth in their respiratory samples. Three patients had transient NTM infection, two had persistent, and five had active NTM infection (NTM pulmonary disease). Patients with NTM pulmonary disease received antibiogram-directed antimycobacterial therapy. In patients with NTM pulmonary disease, the median ppFEV1 and BMI decreased by 17% and 1%, respectively, at the time of the first NTM isolation when compared with the values one year before the first NTM isolation. Culture conversion was not seen in any patient infected with Mycobacteriunm abscessus complex.

CONCLUSIONS

The NTM infection incidence is lower in our country than in those countries where the BCG vaccine is not routinely applied. The BCG vaccine may be a protective factor for NTM infection. Further studies are needed about the prevalence of NTM infections, facilitating and protective factors, and appropriate management of NTM infections in patients with CF.

The key factors contributing to the risk, diagnosis and treatment of non-tuberculous mycobacterial opportunistic infections

The incidence and prevalence of diseases caused by non-tuberculous mycobacteria (NTM) have been steadily increasing worldwide. NTM are environmental saprophytic organisms; however, a few strains are known to produce diseases in humans affecting pulmonary and extra-pulmonary sites. Although the environment is a major source of NTM infection, recent studies have shown that person-to-person dissemination could be an important transmission route for these microorganisms. Structural and functional lung defects and immunodeficiency are major risk factors for acquiring NTM infections. Diagnosis of NTM diseases is very complex owing to the necessity of distinguishing between a true pathogen and an environmental contaminant. Identification at the species level is critical due to differences in the antibiotic susceptibility patterns of various NTM strains. Such identification is mainly achieved by molecular methods; additionally, mass spectrometry (e.g., MALDI-TOF) is useful for NTM species determination. Natural resistance of NTM species to a wide spectrum of antibiotics makes prescribing treatment for NTM diseases very difficult. NTM therapy usually takes more than one year and requires multi-drug regimens, yet the outcome often remains poor. Therefore, alternatives to antibiotic therapy treatment methods is an area under active exploration. NTM infections are an active global health problem imposing the necessity for better diagnostic tools and more effective treatment methods.

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.

The respiratory microbiome and nontuberculous mycobacteria: an emerging concern in human health

Nontuberculous mycobacteria (NTM) are diverse microbial species encompassing commensals and pathogens with the ability to cause pulmonary disease in both immunocompetent and immunocompromised individuals. In contrast to Mycobacterium tuberculosis, which has seen a reduction in disease rates in developed countries, the incidence and prevalence of NTM disease is increasing. NTM are difficult to treat with standard antimicrobial regimens and may contain both virulence and antibiotic-resistance genes with potential for pathogenicity. With the advent of molecular techniques, it has been elucidated that these organisms do not reside in isolation and are rather part of a complex milieu of microorganisms within the host lung microbiome. Over the last decade, studies have highlighted the impact of the microbiome on host immunity, metabolism and cell-cell communication. This recognition of a broader community raises the possibility that the microbiome may disrupt the balance between infection and disease. Additionally, NTM disease progression and antimicrobial therapy may affect the healthy steady state of the host and function of the microbiome, contributing to further dysbiosis and clinical deterioration. There have been limited studies assessing how NTM may influence the relationship between microbiome and host. In this review, we highlight available studies about NTM and the microbiome, postulate on virulence mechanisms by which these microorganisms communicate and discuss implications for treatment.

Same Game, Different Players: Emerging Pathogens of the CF Lung

Incidences of non-tuberculosis mycobacteria (NTM) and Aspergillus fumigatus have increased around the world over the past decade and have become a significant health threat to immunocompromised individuals such as those with cystic fibrosis (CF). CF is characterized by the buildup of mucus in the lungs which become chronically infected by a myriad of pathogens.

The survival rates of individuals with cystic fibrosis (CF) have significantly increased as a result of improved therapies, such as the inclusion of cystic fibrosis transmembrane conductance regulator (CFTR) modulators for some mutations. However, microbial infection of the airways remains a significant clinical problem. The well-known pathogens Pseudomonas aeruginosa and Staphylococcus aureus continue to establish difficult-to-treat infections in the CF lung. However, in recent years, there has been an increased prevalence of both Aspergillus fumigatus (Af) and non-tuberculous mycobacteria (NTM) species isolated from CF patient sputa. The emergence of these pathogens opens an important area of discussion about multikingdom infections, specifically, how interspecies interactions have the potential to shape the course of infection, such as tolerance to host immune defenses and antimicrobial therapies. Their ability to establish themselves in an existing polymicrobial environment suggests to us that microbial interactions play a significant role, and characterizing these mechanisms and understanding their implications will be critical to the future development of better antimicrobial therapies. With this minireview, we hope to inspire conversations about and demonstrate the merit of more research in this area.

Risk factors for nontuberculous mycobacterial isolation in patients with cystic fibrosis: A meta-analysis

BACKGROUND

To better understand the mechanisms of infection with nontuberculous mycobacteria (NTM) in patients with cystic fibrosis (CF), we explore different risk factors associated with NTM positivity in a meta-analysis.

METHODS

Studies published before 31 July 2019 were selected from MEDLINE. Combined odds ratios (ORs) were calculated by pooling the ORs of each study. The weighted mean difference (WMD) was used for continuous numerical measurements. Summary data were pooled using fixed- or random-effects models according to the presence of heterogeneity (P < .1 or I²  > 50%).

RESULTS

Nineteen studies with a total of 23 418 patients, of whom 1421 (6%) were diagnosed as NTM positive, were included. Older age was significantly associated with NTM positivity (WMD = 2.12, 95% confidence interval [CI]: 1.11-3.13; P < .01, fixed-effects model). The OR for Staphylococcus aureus colonization was 1.66 (95% CI: 1.21-2.26; P = .001) in 11 studies (8091 patients), the OR for Aspergillus fumigatus colonization was 3.59 (95% CI: 3.05-4.23; P < .001) in 11 studies (20 480 patients), and the OR for Stenotrophomonas maltophilia colonization was 3.41 (95% CI: 2.66-4.39; P < .01) in seven studies (14 935 patients). Oral corticosteroids were significantly associated with NTM positivity (OR = 1.98, 95% CI: 1.24-3.16; P < .01, 6 studies, 1936 patients). No other factor showed a significant association.

CONCLUSION

Older age, S. aureus, S. maltophilia, and A. fumigatus chronic colonization, and oral corticosteroids were significantly associated with an increased risk of NTM positivity. CF patients with more severe conditions should be closely monitored for NTM.

A Comparative Genomics Approach for Shortlisting Broad-Spectrum Drug Targets in Nontuberculous Mycobacteria

Many members of nontuberculous mycobacteria (NTM) are opportunistic pathogens causing several infections in animals. The incidence of NTM infections and emergence of drug-resistant NTM strains are rising worldwide, emphasizing the need to develop novel anti-NTM drugs. The present study is aimed to identify broad-spectrum drug targets in NTM using a comparative genomics approach. The study identified 537 core proteins in NTM of which 45 were pathogen specific and essential for the survival of pathogens. Furthermore, druggability analysis indicated that 15 were druggable among those 45 proteins. These 15 proteins, which were core proteins, pathogen-specific, essential, and druggable, were considered as potential broad-spectrum candidates. Based on their locations in cytoplasm and membrane, targets were classified as drug and vaccine targets. The identified 15 targets were different enzymes, carrier proteins, transcriptional regulator, two-component system protein, ribosomal, and binding proteins. The identified targets could further be utilized by researchers to design inhibitors for the discovery of antimicrobial agents.

CFTR Depletion Confers Hypersusceptibility to Mycobacterium fortuitum in a Zebrafish Model

The Mycobacterium fortuitum complex comprises several closely related species, causing pulmonary and extra-pulmonary infections. However, there is very limited knowledge about the disease pathogenesis involved in M. fortuitum infections, particularly due to the lack of suitable animal models. Using the zebrafish model, we show that embryos are susceptible to M. fortuitum infection in a dose-dependent manner. Furthermore, zebrafish embryos form granulomas from as early as 2 days post-infection, recapitulating critical aspects of mycobacterial pathogenesis observed in other pathogenic species. The formation of extracellular cords in infected embryos highlights a previously unknown pathogenic feature of M. fortuitum. The formation of large corded structures occurs also during in vitro growth, suggesting that this is not a host-adapted stress mechanism deployed during infection. Moreover, transient macrophage depletion led to rapid embryo death with increased extracellular cords, indicating that macrophages are essential determinants of M. fortuitum infection control. Importantly, morpholino depletion of the cystic fibrosis transmembrane conductance regulator (cftr) significantly increased embryo death, bacterial burden, bacterial cords and abscesses. There was a noticeable decrease in the number of cftr-deficient infected embryos with granulomas as compared to infected controls, suggesting that loss of CFTR leads to impaired host immune responses and confers hypersusceptiblity to M. fortuitum infection. Overall, these findings highlight the application of the zebrafish embryo to study M. fortuitum and emphasizes previously unexplored aspects of disease pathogenesis of this significant mycobacterial species.

Genomic Analysis of Mycobacterium abscessus Complex Isolates Collected in Ireland between 2006 and 2017

Members of the Mycobacterium abscessus complex (MABC) are multidrug-resistant nontuberculous mycobacteria and cause opportunistic pulmonary infections in individuals with cystic fibrosis (CF). In this study, genomic analysis of MABC isolates was performed to gain greater insights into the epidemiology of circulating strains in Ireland. Whole-genome sequencing (WGS) was performed on 70 MABC isolates that had been referred to the Irish Mycobacteria Reference Laboratory between 2006 and 2017 across nine Irish health care centers. The MABC isolates studied comprised 52 isolates from 27 CF patients and 18 isolates from 10 non-CF patients. WGS identified 57 (81.4%) as M. abscessus subsp. abscessus, 10 (14.3%) as M. abscessus subsp. massiliense, and 3 (4.3%) as M. abscessus subsp. bolletii Forty-nine (94%) isolates from 25 CF patients were identified as M. abscessus subsp. abscessus, whereas 3 (6%) isolates from 2 CF patients were identified as M. abscessus subsp. massiliense Among the isolates from non-CF patients, 44% (8/18) were identified as M. abscessus subsp. abscessus, 39% (7/18) were identified as M. abscessus subsp. massiliense, and 17% (3/18) were identified as M. abscessus subsp. bolletii WGS detected two clusters of closely related M. abscessus subsp. abscessus isolates that included isolates from different CF centers. There was a greater genomic diversity of MABC isolates among the isolates from non-CF patients than among the isolates from CF patients. Although WGS failed to show direct evidence of patient-to-patient transmission among CF patients, there was a predominance of two different strains of M. abscessus subsp. abscessus Furthermore, some MABC isolates were closely related to global strains, suggesting their international spread. Future prospective real-time epidemiological and clinical data along with contemporary MABC sequence analysis may elucidate the sources and routes of transmission among patients infected with MABC.

Out-Smarting the Host: Bacteria Maneuvering the Immune Response to Favor Their Survival

Bacteria adapt themselves to various environmental conditions in nature, which can lead to bacterial adaptation and persistence in the host as commensals or pathogens. In healthy individuals, host defense mechanisms prevent the opportunistic bacteria/commensals from becoming a pathological infection. However, certain pathological conditions can impair normal defense barriers leading to bacterial survival and persistence. Under pathological conditions such as chronic lung inflammation, bacteria employ various mechanisms from structural changes to protease secretion to manipulate and evade the host immune response and create a niche permitting commensal bacteria to thrive into infections. Therefore, understanding the mechanisms by which pathogenic bacteria survive in the host tissues and organs may offer new strategies to overcome persistent bacterial infections. In this review, we will discuss and highlight the complex interactions between airway pathogenic bacteria and immune responses in several major chronic inflammatory diseases such as asthma and chronic obstructive pulmonary disease (COPD).

Lymphocyte responses to Mycobacterium tuberculosis and Mycobacterium bovis are similar between BCG-vaccinated patients with cystic fibrosis and healthy controls

BACKGROUND

The low rate of nontuberculous mycobacteria (NTM) among Brazilian patients with cystic fibrosis (CF) may be due to cross-reactive Bacille Calmette-Guérin (BCG) vaccination. In the present pilot study, we aimed to compare the lymphocyte responses against Mycobacterium tuberculosis(Mtb) and Mycobacterium bovis (BCG) in BCG-vaccinated CF patients and healthy controls.

METHODS

The lymphocyte responses of CF patients (n = 10) and healthy controls (n = 10) were assessed in terms of lymphocyte proliferation index (LPI), using flow cytometry. Median rates of each cell subtype - CD4, CD8, γδ T cells and CD19 (B) cells - were also determined.

RESULTS

Median LPIs (CF vs. controls) were 22.9% vs. 13.0% (p = 0.481) and 23.1% vs. 17.6% (p = 0.481), upon stimulation with Mtb and BCG, respectively. Both groups had a predominant CD4 T cell response to Mtb (median rate = 82.5% vs. 79.7%; p = 0.796) and BCG (LPI = 84.3% vs. 83.0%; p = 0.853), which were significantly higher than the CD8, CD19 and γδ responses within both groups. CF patients tended to have a higher CD8 T cell response upon stimulation with the phytohemagglutinin mitogen than healthy controls (median rate = 42.8% vs. 31.7%, p = 0.075).

CONCLUSION

The responses of BCG-vaccinated CF patients to Mtb and BCG are at least similar to those of healthy individuals. These are probably memory responses elicited by the BCG vaccination, which can cross-react with NTM and may explain the low frequency of NTM lung infection in our CF center.

Nontuberculous mycobacterial infections in a Brazilian pediatric population: a seven-year survey

The aim of this study was to describe the frequency of nontuberculous mycobacteria (NTM) isolation and their related outcomes among pediatric patients of a Brazilian university hospital from 2012 to 2019. NTM were identified in different clinical samples by microbiological culture and molecular-based methods. NTM were isolated from 14 patients, out of whom four (27%) were infected and were treated accordingly. Two were infected with Mycobacterium avium complex (MAC), two with M. abscessus complex (MABSC) and one with M. intracellulare. Two patients had cystic fibrosis-related lung disease and improved after successful NTM eradication. One patient was HIV-positive and died. One patient had severe combined immunodeficiency (SCID)-related pneumonia and is currently being followed-up. We conclude that NTM frequency in our center was low among pediatric patients. Whether this is inherent to Brazilian patients, due to the broad coverage of the Bacille Calmette-Guérin (BCG) vaccine in Brazil, or a result of underdiagnosis remains to be elucidated.

Mycobacterium abscessus, an Emerging and Worrisome Pathogen among Cystic Fibrosis Patients

Nontuberculous mycobacteria (NTM) have recently emerged as important pathogens among cystic fibrosis (CF) patients worldwide. Mycobacterium abscessus is becoming the most worrisome NTM in this cohort of patients and recent findings clarified why this pathogen is so prone to this disease. M. abscessus drug therapy takes up to 2 years and its failure causes an accelerated lung function decline. The M. abscessus colonization of lung alveoli begins with smooth strains producing glycopeptidolipids and biofilm, whilst in the invasive infection, "rough" mutants are responsible for the production of trehalose dimycolate, and consequently, cording formation. Human-to-human M. abscessus transmission was demonstrated among geographically separated CF patients by whole-genome sequencing of clinical isolates worldwide. Using a M. abscessus infected CF zebrafish model, it was demonstrated that CFTR (cystic fibrosis transmembrane conductance regulator) dysfunction seems to have a specific role in the immune control of M. abscessus infections only. This pathogen is also intrinsically resistant to many drugs, thanks to its physiology and to the acquisition of new mechanisms of drug resistance. Few new compounds or drug formulations active against M. abscessus are present in preclinical and clinical development, but recently alternative strategies have been investigated, such as phage therapy and the use of β-lactamase inhibitors.

Modifications on C6 and C7 Positions of 3-Phenylquinolone Efflux Pump Inhibitors Led to Potent and Safe Antimycobacterial Treatment Adjuvants

Nontuberculous mycobacteria (NTM) are ubiquitous microbes belonging to the Mycobacterium genus. Among all NTM pathogens, M. avium is one of the most frequent agents causing pulmonary disease, especially in immunocompromised individuals and cystic fibrosis patients. Recently, we reported the first ad hoc designed M. avium efflux pump inhibitor (EPI; 1b) able to strongly boost clarithromycin (CLA) MIC against different M. avium strains. Since the 3-phenylquinolone derivative 1b suffered from toxicity issues toward human macrophages, herein we report a two-pronged medicinal chemistry workflow for identifying new potent and safe NTM EPIs. Initially, we followed a computational approach exploiting our pharmacophore models to screen FDA approved drugs and in-house compounds to identify "ready-to-use" NTM EPIs and/or new scaffolds to be optimized in terms of EPI activity. Although nicardipine 2 was identified as a new NTM EPI, all identified molecules still suffered from toxicity issues. Therefore, based on the promising NTM EPI activity of 1b, we undertook the design, synthesis, and biological evaluation of new 3-phenylquinolones differently functionalized at the C6/C7 as well as N1 positions. Among the 27 synthesized 3-phenylquinolone analogues, compounds 11b, 12b, and 16a exerted excellent NTM EPI activity at concentrations below their CC₅₀ on human cells, with derivative 16a being the most promising compound. Interestingly, 16a also showed good activity in M. avium-infected macrophages both alone as well as in combination with CLA. The antimycobacterial activity observed for 16a only when tested in the ex vivo model suggests a high therapeutic potential of EPIs against M. avium, which seems to need functional efflux pumps to establish intracellular infections.

Quorum Sensing as Antivirulence Target in Cystic Fibrosis Pathogens

Cystic fibrosis (CF) is an autosomal recessive genetic disorder which leads to the secretion of a viscous mucus layer on the respiratory epithelium that facilitates colonization by various bacterial pathogens. The problem of drug resistance has been reported for all the species able to colonize the lung of CF patients, so alternative treatments are urgently needed. In this context, a valid approach is to investigate new natural and synthetic molecules for their ability to counteract alternative pathways, such as virulence regulating quorum sensing (QS). In this review we describe the pathogens most commonly associated with CF lung infections: Staphylococcus aureus, Pseudomonas aeruginosa, species of the Burkholderia cepacia complex and the emerging pathogens Stenotrophomonas maltophilia, Haemophilus influenzae and non-tuberculous Mycobacteria. For each bacterium, the QS system(s) and the molecules targeting the different components of this pathway are described. The amount of investigations published in the last five years clearly indicate the interest and the expectations on antivirulence therapy as an alternative to classical antibiotics.

Dual β-Lactam Combinations Highly Active against Mycobacterium abscessus Complex In Vitro

As a consequence of a growing population of immunocompromised individuals, including transplant recipients and cystic fibrosis patients, there has been a dramatic increase in chronic infections caused by Mycobacterium abscessus complex (MABC) strains that are usually recalcitrant to effective antibiotic therapy. The recent rise of macrolide resistance in MABC has further complicated this clinical dilemma, dramatizing the need for novel agents. The repurposing of current antibiotics is one rapid path from discovery to patient care. In this study, we have discovered that dual β-lactams, and specifically the combination of ceftazidime with either ceftaroline or imipenem, are synergistic and have clinically relevant activities, with MIC50s of 0.25 (ceftaroline with 100 µg/ml ceftazidime) and 0.5 µg/ml (imipenem with 100 µg/ml ceftazidime) against clinical MABC isolates. Similar synergy was observed in time-kill studies against the M. abscessus ATCC 19977 strain using clinically achievable concentrations of either imipenem (4 µg/ml) or ceftaroline (2 µg/ml), as the addition of ceftazidime at concentrations of ≥50 µg/ml showed a persistent bactericidal effect over 5 days. Treatment of THP-1 human macrophages infected with three different M. abscessus clinical isolates supported the in vitro findings, as the combination of 100 µg/ml ceftazidime and 0.125 µg/ml ceftaroline or 100 µg/ml ceftazidime and 0.25 µg/ml imipenem dramatically reduced the CFU counts to near baseline levels of infection. This study's finding that there is synergy between certain β-lactam combinations against M. abscessus infection provides optimism toward identifying an optimum dual β-lactam treatment regimen.IMPORTANCE The emergence of chronic MABC infections among immunocompromised populations and their inherent and acquired resistance to effective antibiotic therapy have created clinical challenges in advancing patients for transplant surgery and treating those with disease. There is an urgent need for new treatment regimens, and the repurposing of existing antibiotics provides a rapid strategy to advance a laboratory finding to patient care. Our recent discoveries that dual β-lactams, specifically the combination of ceftazidime with ceftaroline or ceftazidime with imipenem, have significant in vitro MIC values and kill curve activities and are effective against infected THP-1 human macrophages provide optimism for a dual β-lactam treatment strategy against MABC infections. The unexpected synergistic activities reported in this study create a new path of discovery to repurpose the large family of β-lactam drugs.

Nontuberculous mycobacteria and allergic bronchopulmonary aspergillosisin lung transplant candidate

Airway infections are a key component of cystic fibrosis (CF) lung disease. The approach to common pathogens such as Pseudomonas aeruginosa or Staphilococcus aureus is guided by a significant evidence base, but the treatment of other infections is significant challenge to pharmacotherapy teams. Here we present a specific approach to treatment of chronic infections with non-tuberculous mycobacteria (NTM) anaerobic bacteria and fungi in a 25 year old patient with CF and severely decreased lung function. Also, allergic bronchopulmonary aspegillosis (ABPA) was diagnosed in the patient. Key words: cystic fibrosis, non-tuberculous mycobacteria, allergic bronchopulmonary aspegillosis, antibiotics, systemic steroids

Cystic Fibrosis: Emerging Understanding and Therapies

Cystic fibrosis (CF) is the most common life-limiting genetic disease in Caucasian patients. Continued advances have led to improved survival, and adults with CF now outnumber children. As our understanding of the disease improves, new therapies have emerged that improve the basic defect, enabling patient-specific treatment and improved outcomes. However, recurrent exacerbations continue to lead to morbidity and mortality, and new pathogens have been identified that may lead to worse outcomes. In addition, new complications, such as CF-related diabetes and increased risk of gastrointestinal cancers, are creating new challenges in management. For patients with end-stage disease, lung transplantation has remained one of the few treatment options, but challenges in identifying the most appropriate patients remain.

Airway microbiota in patients with paediatric cystic fibrosis: Relationship with clinical status

INTRODUCTION

New massive sequencing techniques make it possible to determine the composition of airway microbiota in patients with cystic fibrosis (CF). However, the relationship between the composition of lung microbiome and the clinical status of paediatric patients is still not fully understood.

MATERIAL AND METHODS

A cross-sectional observational study was conducted on induced sputum samples from children with CF and known mutation in the CFTR gene. The bacterial sequences of the 16SrRNA gene were analyzed and their association with various clinical variables studied.

RESULTS

Analysis of the 13 samples obtained showed a core microbiome made up of Staphylococcus spp., Streptococcus spp., Rothia spp., Gemella spp. and Granulicatella spp., with a small number of Pseudomonas spp. The cluster of patients with less biodiversity were found to exhibit a greater number of sequences of Staphylococcus spp., mainly Staphylococcus aureus (p 0.009) and a greater degree of lung damage.

CONCLUSION

An airway microbiome with greater biodiversity may be an indicator of less pronounced disease progression, in which case new therapeutic interventions that prevent reduction in non-pathogenic species of the airway microbiota should be studied.

NonTuberculous Mycobacteria infection and lung transplantation in cystic fibrosis: a worldwide survey of clinical practice

BACKGROUND

In people with cystic fibrosis infection with NonTuberculous Mycobacteria is of increasing prevalence. Mycobacterium abscessus complex is of particular concern and has been associated with adverse clinical outcomes. Optimal treatment usually requires multiple antibiotics for over 12 months. When considering lung transplantation for patients with NonTuberculous Mycobacteria potential benefits must be balanced against the risks of uncontrolled infection post-transplant and significant side-effects associated with treatment. In this survey we assessed current international practice with regard to assessing and listing patients for lung transplantation.

METHODS

We designed a questionnaire enquiring about local practice regarding screening for NonTuberculous Mycobacteria infection, specific contra-indications to transplantation, management and segregation of patients pre- and post-transplant. The survey was sent via e-mail to 37 paediatric and adult lung transplant centres across Europe, North America and Australia.

RESULTS

We gathered complete questionnaires from 21 centres (57% response rate). Few centres (29%) have a clear written policy regarding NonTuberculous Mycobacteria. Sixteen (76%) centres require molecular identification of NonTuberculous Mycobacteria species. Only four centres would consider infection with M. abscessus complex in itself a contra-indication for listing, however 76% regard it as a relative contra-indication. Eighty-six percent require treatment pre-transplantation. Finally, only 61% of centres had a clear policy regarding segration of patients pre-transplant and 48% post-transplant.

CONCLUSIONS

The issue of NonTuberculous Mycobacteria infection in people with cystic fibrosis requiring lung transplantation is well-recognized however current international recommendations are not detailed and there is variation in practice between centres. There is an urgent requirement for high quality clinical data to inform decision-making.

Positive Effect of Liposomal Amikacin for Inhalation on Mycobacterium abcessus in Cystic Fibrosis Patients

Mycobacterium abscessus is difficult to eradicate. At the Montpellier CF Center, we prescribed liposomal amikacin for inhalation to 5 patients with M abscessus infection. The 3 patients who completed the treatment did not have any respiratory exacerbation, showed negative cultures for M abscessus in their sputum, and stabilized their spirometric functions.

Phenotypic Optimization of Urea-Thiophene Carboxamides To Yield Potent, Well Tolerated, and Orally Active Protective Agents against Aminoglycoside-Induced Hearing Loss

Hearing loss is a major public health concern with no pharmaceutical intervention for hearing protection or restoration. Using zebrafish neuromast hair cells, a robust model for mammalian auditory and vestibular hair cells, we identified a urea-thiophene carboxamide, 1 (ORC-001), as protective against aminoglycoside antibiotic (AGA)-induced hair cell death. The 50% protection (HC₅₀) concentration conferred by 1 is 3.2 μM with protection against 200 μM neomycin approaching 100%. Compound 1 was sufficiently safe and drug-like to validate otoprotection in an in vivo rat hearing loss model. We explored the structure-activity relationship (SAR) of this compound series to improve otoprotective potency, improve pharmacokinetic properties and eliminate off-target activity. We present the optimization of 1 to yield 90 (ORC-13661). Compound 90 protects mechanosensory hair cells with HC₅₀ of 120 nM and demonstrates 100% protection in the zebrafish assay and superior physiochemical, pharmacokinetic, and toxicologic properties, as well as complete in vivo protection in rats.

Pulmonary disease by non-tuberculous mycobacteria - clinical management, unmet needs and future perspectives

INTRODUCTION

The number of patients with pulmonary disease caused by non-tuberculous mycobacteria (NTM) is increasing globally. Poor resistance against infections, for example, due to pre-existing lung diseases, immune deficiency and immune-modulating treatment, predisposes the population to developing pulmonary NTM disease. The incidence of pre-existing lung diseases such as chronic obstructive pulmonary disease and bronchiectasis has also increased. NTM disease diagnosis is often delayed due to non-specific symptoms. The therapeutic arsenal is limited and adherence to treatment guidelines is often low since the treatment regimens are complex, lengthy and side effects are common. Thus, current disease management is far from satisfactory and needs to be improved. Areas covered: This review provides an overview of the current knowledge of NTM infections and includes pathogenesis, disease patterns, epidemiology, disease management, unmet needs and future perspectives. Expert commentary: NTM disease is becoming more prevalent, in part with our increased awareness and improved diagnostic methods. However, our understanding of the disease pathogenesis is limited and treatment decisions are challenging, with difficult to employ drug regimens. Optimal management requires collaboration between healthcare providers, patients and expert centers.

Nitazoxanide Analogs Require Nitroreduction for Antimicrobial Activity in Mycobacterium smegmatis

In this study, we aimed to decipher the natural resistance mechanisms of mycobacteria against novel compounds isolated by whole-cell-based high-throughput screening (HTS). We identified active compounds using Mycobacterium aurum. Further analyses were performed to determine the resistance mechanism of M. smegmatis against one hit, 3-bromo-N-(5-nitrothiazol-2-yl)-4-propoxybenzamide (3), which turned out to be an analog of the drug nitazoxanide (1). We found that the repression of the gene nfnB coding for the nitroreductase NfnB was responsible for the natural resistance of M. smegmatis against 3. The overexpression of nfnB resulted in sensitivity of M. smegmatis to 3. This compound must be metabolized into hydroxylamine intermediate for exhibiting antibacterial activity. Thus, we describe, for the first time, the activity of a mycobacterial nitroreductase against 1 analogs, highlighting the differences in the metabolism of nitro compounds among mycobacterial species and emphasizing the potential of nitro drugs as antibacterials in various bacterial species.

Inhaled Antibiotic Therapy in Chronic Respiratory Diseases

The management of patients with chronic respiratory diseases affected by difficult to treat infections has become a challenge in clinical practice. Conditions such as cystic fibrosis (CF) and non-CF bronchiectasis require extensive treatment strategies to deal with multidrug resistant pathogens that include Pseudomonas aeruginosa, Methicillin-resistant Staphylococcus aureus, Burkholderia species and non-tuberculous Mycobacteria (NTM). These challenges prompted scientists to deliver antimicrobial agents through the pulmonary system by using inhaled, aerosolized or nebulized antibiotics. Subsequent research advances focused on the development of antibiotic agents able to achieve high tissue concentrations capable of reducing the bacterial load of difficult-to-treat organisms in hosts with chronic respiratory conditions. In this review, we focus on the evidence regarding the use of antibiotic therapies administered through the respiratory system via inhalation, nebulization or aerosolization, specifically in patients with chronic respiratory diseases that include CF, non-CF bronchiectasis and NTM. However, further research is required to address the potential benefits, mechanisms of action and applications of inhaled antibiotics for the management of difficult-to-treat infections in patients with chronic respiratory diseases.