Treatment for non-tuberculous mycobacteria: challenges and prospects

Synthesis and evaluation of Trehalose-Pks13 inhibitor conjugates targeting mycobacteria

One obstacle to developing new drugs targeting Mycobacterium tuberculosis (Mtb) is its unique cell wall, which forms a significant permeability barrier to drug transport. Recently, transporters of trehalose and other disaccharides within this structure have been identified. We hypothesized that conjugating small molecules active against Mtb with trehalose could facilitate selective uptake of the trehalose conjugate into the cell. This strategy might enhance penetration of the hydrophobic mycomembrane or enable selective targeting of mycobacteria. To test this hypothesis, we used Cu(I)-catalyzed azide-alkyne Huisgen cycloaddition to conjugate 6-azido trehalose to known polyketide synthase 13 (Pks13) inhibitors, such as 2-aminothiophenes (AT), and benzofurans (BzF) with alkyne moieties, and tested the conjugates' activity against mycobacteria. We found that, in some instances, trehalose served to significantly enhance either the antimycobacterial potency or improve selectivity (by reducing toxicity) of the Pks13 inhibitors. Somewhat surprisingly, in M. smegmatis (Msm), the activity of trehalose-modified AT derivatives was independent of the trehalose transporter LpqY-SugABC, suggesting an alternative mechanism(s) of passage into the cell. Thus, the mechanisms underlying trehalose-enhanced inhibitor activity remains to be elucidated. Future studies applying this Trojan Horse strategy to alternative inhibitor chemotypes will be needed to assess the potential of this approach to overcoming the mycomembrane permeability barrier.

The gut-lung axis and microbiome dysbiosis in non-tuberculous mycobacterial infections: immune mechanisms, clinical implications, and therapeutic frontiers

Non-tuberculous mycobacteria (NTM) are emerging pathogens of global concern, particularly in regions with declining tuberculosis rates. This review synthesizes current evidence on the epidemiology, immune pathogenesis, and microbiome interactions underlying NTM infections. The rising incidence of NTM is driven by environmental factors, immunocompromised populations, and advanced diagnostics. Clinically, NTM manifests as pulmonary, lymphatic, skin/soft tissue, or disseminated disease, with Mycobacterium avium complex (MAC) and M. abscessus being predominant pathogens. Host immunity, particularly Th1 responses mediated by IL-12/IFN-γ and TLR2 signaling, is critical for controlling NTM, while dysregulated immunity (e.g., elevated Th2 cytokines, PD-1/IL-10 pathways) exacerbates susceptibility. Emerging research highlights the gut-lung axis as a pivotal mediator of disease, where microbiome dysbiosis-marked by reduced Prevotella and Bifidobacterium-impairs systemic immunity and promotes NTM progression. Short-chain fatty acids (SCFAs) and microbial metabolites like inosine modulate macrophage and T-cell responses, offering therapeutic potential. Studies reveal distinct airway microbiome signatures in NTM patients, characterized by enriched Streptococcus and Prevotella, and reduced diversity linked to worse outcomes. Despite advances, treatment remains challenging due to biofilm formation, antibiotic resistance, and relapse rates. This review underscores the need for microbiome-targeted therapies, personalized medicine, and longitudinal studies to unravel causal relationships between microbial ecology and NTM pathogenesis.

New Frontiers in Fighting Mycobacterial Infections: Venom-Derived Peptides

Notwithstanding the indefatigable endeavors to develop effective anti-mycobacterial therapies, mycobacterial infections still present a tough problem for medicine today. The problem is further complicated by the disquieting surge of drug-resistant mycobacterial pathogens, which considerably narrows the existing therapeutic options. Thus, there is a genuine need to discover novel anti-mycobacterial drugs. Animal venoms are considered a treasure trove of structurally variable and biologically active peptides, which may hold promise for therapeutic applications. Over the past two decades, abundant evidence has been amassed regarding anti-mycobacterial effects of various peptides derived from the venoms of honeybees, wasps, scorpions, pseudoscorpions, cone snails, and snakes. This review intends to consolidate the state-of-the-art knowledge on the anti-mycobacterial peptides of animal venoms and to sketch potentially fruitful directions for future investigations. The available data indicate that micromolar concentrations of particular venom-derived peptides can effectively inhibit the in vitro growth of Mycobacterium tuberculosis and non-tuberculous mycobacteria. The proposed mechanisms of action of venom-derived peptides include reduced activity of plasma membrane ATPase, depolarization of the cell membrane, disruption of the cell wall, and increased generation of reactive oxygen species. Interestingly, administering certain peptides (≤ 2 mg/kg body weight) through daily intraperitoneal injections to mice for 8 consecutive days resulted in lower levels of mycobacterial infections and inflammation, hitting two targets with one arrow. Indubitably, such peptides can usher in new possibilities for the prevention and treatment of recalcitrant mycobacterial infections.

Targeting Autophagy as a Strategy for Developing New Host-Directed Therapeutics Against Nontuberculous Mycobacteria

Nontuberculous mycobacteria (NTMs) are increasingly being recognized as opportunistic pathogens in clinical practice because of their innate resistance to antimicrobial treatment and the widespread increase in multidrug-resistant strains on a global scale. NTMs pose a tremendous infection management challenge, especially in individuals with pre-existing lung conditions, as well as those who are immunocompromised. NTMs' capability to evade or suppress the immune responses of their host is a key feature that makes them a cause of persistent chronic infection. Autophagy, an essential cellular defense mechanism that delivers and breaks down intracellular materials in lysosomes, protects the host from mycobacterial infection. Initial studies have revealed encouraging therapeutic strategies that augment endogenous autophagic mechanisms or block harmful host responses, thus having the potential to decrease intracellular mycobacterial infection, including that caused by multidrug-resistant strains. This review discusses how NTMs can evade autophagic mechanisms and considers the possibilities of using autophagy-inducing agents to develop novel therapeutic strategies to combat NTM infection.

Susceptibility of Non-Tuberculous Mycobacteria Biofilm to Common Disinfectants in Aquaculture Systems

Mycobacteriosis is a common and persistent bacterial disease affecting cultured, wild and pet fish. The disease can be caused by various Mycobacterium spp. Currently, depopulation and disinfection are the main recommended measures for containing disease outbreaks, as no vaccines are commercially available, and only a few reports of successful antimicrobial therapies have been made. While disinfectant susceptibility studies have been conducted on planktonic forms of some non-tuberculous mycobacteria (NTM) affecting fish, biofilm-related research remains limited. In this study, biofilm formation of Mycobacterium chelonae, Mycobacterium salmoniphilum, Mycobacterium arcueilense and Mycobacterium marinum isolates recovered from diseased fish were initially evaluated using the minimal biofilm eradication concentration (MBEC) assay system. All Mycobacterium spp. were able to form biofilms within a 2-week period when incubated at 25°C, but M. chelonae, M. salmoniphilum and M. arcueilense produced a faster and greater biofilm than M. marinum. To investigate the susceptibility of mycobacterial biofilms to common disinfectants, mature biofilms were divided into six treatment groups based on disinfectant type and exposure time: povidone-iodine (50 mg L-1 free iodine) and bleach (200 mg L-1 free chlorine) were applied for 30 min each; hydrogen peroxide (3% H2O2) and Virkon Aquatic (10 g L-1) were applied for 15 min each; and 70% ethanol was tested at both 15 and 30 min. Results demonstrated variable susceptibility among species. M. marinum was susceptible to all disinfectants, while M. arcueilense was susceptible to bleach, povidone-iodine and 70% ethanol (30-min exposure). None of the tested disinfectants at recommended doses effectively eradicated M. chelonae or M. salmoniphilum biofilms. These findings underscore species-specific differences in biofilm formation and resistance, emphasising the critical need for robust disinfection protocols in aquaculture settings to prevent mycobacteriosis transmission. Further research is essential to understand the mechanisms underlying disinfectant resistance among NTMs, optimise disinfection strategies and ensure the health and biosecurity of aquaculture facilities.

Characterization of mycobacteria isolated from the Brazilian Atlantic Forest: a public health and bioprospection perspective

The Mycobacterium genus remains highly relevant today due to the rising incidence of tuberculosis and opportunistic infections caused by environmental mycobacteria. While much is known about M. tuberculosis, M. leprae and M. bovis, studies focusing on environmental mycobacteria remain limited. These microorganisms are globally distributed and have been identified in diverse biomes, including the Atlantic Forest. This study aims to provide a characterization of four mycobacterial strains isolated from the Atlantic Forest, assessing their metabolic capabilities and biotechnological potential. We investigated the presence of cellulases and proteases and conducted an initial profiling of secreted proteins. Furthermore, the examination of shared antigens and infection kinetics within macrophages offered insights into the ecological and pathogenic potential of these isolates. From a public health perspective, antigenic similarities between these environmental microorganisms and the BCG vaccine strain may influence the efficacy of BCG in protecting against diseases such as tuberculosis. Continued research on these and other environmental isolates, particularly within Brazil's highly biodiverse ecosystems, holds promise for advancing scientific knowledge and contributing to human health.

LeuRS-Targeting Prodrug, MRX-5, Expresses Anti-Mycobacterium abscessus Activity

Mycobacterium abscessus is a multi-drug resistant pathogen presenting significant treatment challenges. This study evaluated MRX-5, an oral prodrug of the leucyl-tRNA synthetase inhibitor MRX-6038, for its efficacy against M. abscessus both in vitro and in vivo. Stability testing of MRX-5 was conducted using liquid chromatography-tandem mass spectrometry in Middlebrook 7H9 broth at 35°C. Following this, the minimum inhibitory concentrations of MRX-5 were determined against two reference strains and 17 clinical isolates of M. abscessus. In the in vivo experiments, the pharmacokinetic properties of MRX-5 were assessed first, followed by efficacy testing conducted in a neutropenic BALB/c mouse model of M. abscessus lung infection. Remarkably, the conversion of MRX-5 to MRX-6038 in liquid broth was complete within 72 h, and MRX-5 demonstrated reduced potency compared to MRX-6038 in vitro. In vivo, MRX-5 was efficiently converted to MRX-6038, achieving an oral bioavailability of 83.95% and significant lung distribution. In the mouse model of pulmonary M. abscessus infection, MRX-5 effectively reduced bacterial load and exhibited antimicrobial activity comparable to that of linezolid. In conclusion, MRX-5 exhibited favourable lung distribution and in vivo efficacy against M. abscessus, positioning it as a promising candidate for the oral treatment of M. abscessus infections.

Essential Oils and their Active Constituents Effective against Non-growing Mycobacterium intracellulare

BACKGROUND

Mycobacterium intracellulare (M. intracellulare) is a common, slow-growing opportunistic pathogen that can cause chronic pulmonary and extrapulmonary infections. Despite its rising incidence, standard treatments are often ineffective in eradicating M. intracellulare, leading to prolonged treatment and high recurrence rates, likely due to persistence of non-growing bacteria. Although essential oils are known for their antimicrobial properties, their effects on M. intracellulare, particularly in its non-growing phase, have not been well studied.

METHODS

We screened 151 essential oils to assess their antimicrobial activity against stationary-phase non-growing M. intracellulare. Essential oils with significant activity were further evaluated at different concentrations by MIC and drug exposure tests.

RESULTS

Thirty-four essential oils were found to have activity at 5000 µg/mL, with 18 showing effectiveness at 1250 µg/mL. Six essential oils, Ajwain, Oregano, Palmarosa, Thyme, Mountain Savory, and Litsea Cubeba had the highest activity, achieving 100% bacterial clearance after one day exposure. Carvacrol, the key active component of Ajwain, Oregano, Thyme, Mountain Savory, eradicated stationary-phase bacteria at 310 µg/mL concentration within one day, while citronellol, the active component of Palmarosa, at 630 µg/mL achieved complete clearance after three day exposure.

CONCLUSIONS

We have newly identified several essential oils, including Ajwain, Oregano, Thyme, Mountain Savory, Palmarosa, and Litsea Cubeba and their active components such as carvacrol and citronellol, to have promising activity against M. intracellulare, and these findings may have implications for developing improved treatments for M. intracellulare infections.

Clinical Characteristics of Nontuberculous Mycobacterial Positivity Occurring During Multidrug-Resistant Tuberculosis Treatment: A Retrospective Study

The clinical characteristics of multidrug-resistant tuberculosis (MDR-TB) patients with concurrent nontuberculous mycobacterial (NTM) infection present significant challenges to treatment. This study investigated the clinical characteristics of MDR-TB patients with concurrent NTM infection during treatment. A retrospective cohort study was conducted to collect the clinical data of MDR-TB patients who initiated treatment between January 2020 and December 2022. A total of 389 patients were analyzed, among which 111 patients who were lost to follow-up and 56 patients who missed etiological examination of tuberculosis during the visit period were excluded. A total of 222 patients with complete data were included in this study. The species identification method primarily employed molecular biology techniques, specifically the DNA microarray method and/or MPB64 antigen detection using the colloidal gold method. Patients whose sputum or bronchoalveolar lavage fluid cultures were positive and who were identified at least once as having NTM or as MPB64 negative were included in this study. Imaging data, comorbidities, pre-treatment infection, and nutritional indicators were analyzed during treatment. Among the 222 MDR-TB patients, no concurrent NTM cases were identified at the beginning of treatment. However, 19 cases (8.56%) were presumed to be NTM-positive during treatment, which appeared during anti-tuberculosis treatment from 2 to 12 months, averaging 6 (3, 12) months. Thirteen patients were only tested for MPB64, with five having two negative MPB64 tests. The symptoms of NTM-positive patients varied, and imaging findings were similar to those of MDR-TB but did not worsen. The emergence of presumed NTM-positive cases (8.56%) among MDR-TB patients during treatment highlights the need for monitoring, as symptoms and imaging findings may mimic MDR-TB without worsening. Early and repeated testing, including methods beyond MPB64, may be useful for more accurate diagnosis and tailored management.

Analysis of relative genes expression and mutation of pstB and efpA efflux pumps in Mycobacterium simiae isolates from suspected tuberculosis patients by using quantitative Real-time PCR

BACKGROUND

Mycobacterium simiae is commonly found in people with weak immune systems such as the elderly and people with tuberculosis and other lung diseases. The aim of this study is the epidemiology of M. simiae infections in Iran and the world, therefore, in this study, analysis of relative gene expression and mutation of pstB and efpA efflux pumps in Mycobacterium simiae isolates from suspected tuberculosis patients by using Real-time quantitative PCR. Sixty-five sputa samples of suspected tuberculosis specimens were collected. The identification of NTM Species by PCR sequencing and determining drug sensitivity by micro broth dilution method. The investigate mutations in pstB and efpA efflux pump genes using the PCR-sequencing method. Comparative evaluation of the replication efficiency of internal control gene 16SrDNA and target genes pstB and efpA.

RESULTS

In total, 15 isolates of M. simiae were evaluated and a drug sensitivity test was performed for them against the antibiotic ethambutol, moxifloxacin, clarithromycin, and linezolid. The highest resistance to moxifloxacin and linezolid antibiotics and the lowest resistance to clarithromycin antibiotics were observed. The results of expression levels of two efflux PstB and efpA showed that there was a significant difference in the expression level of the efpA efflux pump gene in M. simiae three-resistant and double-resistant isolates compared to the sensitive group and the standard.

CONCLUSIONS

The high level of antibiotic resistance In M. simiae isolates is an alarm and monitoring all factors related to antibiotic resistance, including efflux pumps, is an important research topic.

Mycobacterium abscessus subsp. massiliense: Biofilm Formation, Host Immune Response, and Therapeutic Strategies

Infection by Mycobacterium abscessus subsp. massiliense poses a growing public health threat, especially to immunocompromised individuals. The pathogenicity of this mycobacterium is directly linked to its ability to form biofilms, complex structures that confer resistance to antibiotics and the host immune response. The extracellular matrix of the biofilm acts as a physical barrier, hindering the penetration of drugs and the action of the immune system, while also inducing a slow-growth state that reduces susceptibility to antibiotics. Current therapies, which involve prolonged use of multiple antibiotics, are often ineffective and cause significant side effects. Therefore, it is essential to explore new strategies targeting bacterial resistance and biofilm destruction. This narrative review explores the biofilm-forming capacity of Mycobacterium abscessus subsp. massiliense and the potential of novel therapeutic strategies. Promising approaches include inhibiting biofilm formation, developing drugs with improved penetration of the extracellular matrix, combination therapies with agents that destabilize the biofilm structure, and modulating the host immune response. Investing in research and development of new therapeutic strategies is essential to combat this resistant bacterium and improve patient outcomes.

Rational Exploration of 2,4-Diaminopyrimidines as DHFR Inhibitors Active against Mycobacterium abscessus and Mycobacterium avium, Two Emerging Human Pathogens

Nontuberculous mycobacteria (NTM) are emerging human pathogens linked to severe pulmonary diseases. Current treatments involve the prolonged use of multiple drugs and are often ineffective. Bacterial dihydrofolate reductase (DHFR) is a key enzyme targeted by antibiotics in Gram-negative bacterial infections. However, existing DHFR inhibitors designed for Gram-negative bacteria often fail against mycobacterial DHFRs. Here, we detail the rational design of NTM DHFR inhibitors based on P218, a malarial DHFR inhibitor. We identified compound 8, a 2,4-diaminopyrimidine exhibiting improved pharmacological properties and activity against purified DHFR, and whole cell cultures of two predominant NTM species: Mycobacterium avium and Mycobacterium abscessus. This study underscores the potential of compound 8 as a promising candidate for the in vivo validation of DHFR as an effective treatment against NTM infections.

Facial cutaneous tuberculosis infected by non-tuberculous mycobacteria

BACKGROUND

Cutaneous infections caused by non-tuberculous mycobacteria (NTM) are extremely rare, particularly when they are localized to the facial area. This condition presents significant diagnostic challenges due to its unusual presentation and the need for precise microbiological identification.

CASE PRESENTATION

A two-year-old male patient presented with a progressively enlarging reddish-brown mass on the left side of his face. Despite the absence of systemic symptoms, the lesion's growth warranted investigation due to its growth. Ultrasonography showed a hypoechoic mass in the dermis, indicating an underlying abscess. The subsequent aspiration resulted in pale yellow pus, which upon testing and culture, confirmed the presence of Mycobacterium avium complex infection, a species of NTM. This case exemplifies the synergy between imaging modalities and microbiological analysis, highlighting the crucial role of both in achieving favorable clinical outcomes in patients with suspected cutaneous NTM infections. Ultrasound can expedite diagnosis, improve treatment planning, and enhance patient care by enabling targeted interventions and monitoring response to therapy in these scenarios. However, it is the combination of pathogen-specific diagnostics that ensures accurate etiological attribution and appropriate antimicrobial stewardship.

CONCLUSION

Although rare, facial cutaneous infections caused by NTM still deserve thorough investigation to determine the exact cause. Ultrasound is used to identify cutaneous lesions, measure their extent, and guide surgical procedures. The ultimate diagnosis is based on microbiological confirmation.

New antibiofilm strategies for the management of nontuberculous mycobacteria diseases

INTRODUCTION

Nontuberculous mycobacteria (NTM) represent a group of microorganisms comprising more than 190 species. NTM infections have increased recently, and their treatment is a major challenge because to their resistance to conventional treatments. This review focuses on innovative strategies aimed at eradicating NTM biofilms, a critical factor in their resistance. Important areas addressed include biofilm formation mechanisms, current therapeutic challenges, and novel treatment approaches. The main objective is to compile and analyze information on these emerging strategies, identifying pivotal research directions and recent advancements.

AREAS COVERED

A review of the scientific literature was conducted to identify emerging novel therapies for the treatment of NTM infections and to explore potential synergies with existing treatments.

EXPERT OPINION

Experts highlights a limited understanding of optimal treatment regimens, often supported by insufficient scientific evidence. Current therapies are typically prolonged, involve multiple antibiotics with adverse effects, and frequently do not achieve patient cure. Certain species are even considered virtually impossible to eradicate. A thorough understanding of these new approaches is imperative for improving patients outcomes. This review provides a robust foundation for developing of more effective antibacterial strategies, which are essential because of the increasing incidence of NTM infections and the limitations of existing therapies.