Alternative and Experimental Therapies of Mycobacterium abscessus Infections

Engineered phages in anti-infection and anti-tumor fields: A review

The abuse of antibiotics has led to the widespread emergence of multi-drug resistant bacteria. Phage therapy holds promise for enhancing anti-bacterial and anti-infection strategies. Traditional phage therapy employs phage preparations as an alternative to antibiotics for the eradication of bacteria, aiming to achieve the desired clinical outcomes. Modification of phage by transgene or chemical modification overcomes the limitations of traditional phage therapy, including host spectrum modification, bacterial resistance reversal, antigen presentation, and drug targeted delivery, and thus broadens the application field of phages. This article summarizes the progress of engineered phages in the fields of anti-bacterial, anti-infective and anti-tumor therapy. It emphasizes the advantages of engineered phages in anti-bacterial and anti-tumor treatment, and discusses the widespread potential of phage-based modular design as multifunctional biopharmaceuticals, drug carriers, and other applications.

The autophagy-targeting compound V46 enhances antimicrobial responses to Mycobacteroides abscessus by activating transcription factor EB

Mycobacteroides abscessus (Mabc) is a rapidly growing nontuberculous mycobacterium that poses a considerable challenge as a multidrug-resistant pathogen causing chronic human infection. Effective therapeutics that enhance protective immune responses to Mabc are urgently needed. This study introduces trans-3,5,4'-trimethoxystilbene (V46), a novel resveratrol analogue with autophagy-activating properties and antimicrobial activity against Mabc infection, including multidrug-resistant strains. Among the resveratrol analogues tested, V46 significantly inhibited the growth of both rough and smooth Mabc strains, including multidrug-resistant strains, in macrophages and in the lungs of mice infected with Mabc. Additionally, V46 substantially reduced Mabc-induced levels of pro-inflammatory cytokines and chemokines in both macrophages and during in vivo infection. Mechanistic analysis showed that V46 suppressed the activation of the protein kinase B/Akt-mammalian target of rapamycin signaling pathway and enhanced adenosine monophosphate-activated protein kinase signaling in Mabc-infected cells. Notably, V46 activated autophagy and the nuclear translocation of transcription factor EB, which is crucial for antimicrobial host defenses against Mabc. Furthermore, V46 upregulated genes associated with autophagy and lysosomal biogenesis in Mabc-infected bone marrow-derived macrophages. The combination of V46 and rifabutin exerted a synergistic antimicrobial effect. These findings identify V46 as a candidate host-directed therapeutic for Mabc infection that activates autophagy and lysosomal function via transcription factor EB.

Combination of Imipenem-Cilastatin-Relebactam and Amoxicillin in the Antibiotic Regimen in Two Cases of Mycobacterium abscessus Lung Infection

Mycobacterium abscessus is a difficult-to-treat, multidrug-resistant human pathogen. Relebactam has been shown to inhibit M. abscessus β-lactamase (BLAMab) and increase the activity of imipenem and amoxicillin. We present two cases of lung infection due to M. abscessus, one caused by M. abscessussubsp. massiliense and the other by subsp. abscessus. Both strains showed moderate sensitivity to imipenem, and the second strain was also resistant to macrolides. A multidrug antibiotic regimen was administered in both cases, which included imipenem/cilastatin/relebactam adjusted to the estimated glomerular filtration rate (eGFR) and amoxicillin for three months. The regimen was well tolerated and both patients improved both clinically and radiologically after the first phase of treatment. The results of our patients indicate that the combination of imipenem/cilastatin/relebactam and amoxicillin could be used in the future in difficult infections by M. abscessus.

Alternative therapies against Mycobacterium abscessus infections

BACKGROUND

Mycobacterium abscessus (Mab) is considered as the most pathogenic rapid-growing mycobacteria in humans, causing pulmonary and extra-pulmonary diseases, especially in patients with cystic fibrosis. Mab shows intrinsic and acquired resistance to many drugs, leaving limited treatment options that lead to a generally poor prognosis. The standard therapeutic regimen last for more than 6 months and consists of a drug cocktail that ideally includes a macrolide and amikacin. Yet, toxicity and efficacy are suboptimal due also to the high toxicity. There is a need to introduce innovative and out-of-the-box approaches to improve treatments.

OBJECTIVES

In this narrative review, we summarize the recent research on the alternative strategies proposed and discuss the importance of using appropriate experimental assays to assess their activity.

SOURCES

Included articles were identified by searching PubMed and MEDLINE until June 2023. The search terms were 'Mycobacterium abscessus', 'antimicrobial', and 'alternative therapies'. Additional relevant references were obtained from articles retrieved from the primary search.

CONTENT

Therapies against Mab including host directed therapies, repurposed drugs, phage therapy, anti-virulence strategies, essential oils, and inhalation therapies.

IMPLICATIONS

Alternative treatments may represent a valid tool to cope the burden of antimicrobial resistance in Mab-caused diseases.

Structural basis for specific inhibition of salicylate synthase from Mycobacterium abscessus

Blocking iron uptake and metabolism has been emerging as a promising therapeutic strategy for the development of novel antimicrobial compounds. Like all mycobacteria, M. abscessus (Mab) has evolved several countermeasures to scavenge iron from host carrier proteins, including the production of siderophores, which play a crucial role in these processes. In this study, we solved, for the first time, the crystal structure of Mab-SaS, the first enzyme involved in the biosynthesis of siderophores. Moreover, we screened a small, focused library and identified a compound exhibiting a potent inhibitory effect against Mab-SaS (IC50 ≈ 2 μM). Its binding mode was investigated by means of Induced Fit Docking simulations, performed on the crystal structure presented herein. Furthermore, cytotoxicity data and pharmacokinetic predictions revealed the safety and drug-likeness of this class of compounds. Finally, the crystallographic data were used to optimize the model for future virtual screening campaigns. Taken together, the findings of our study pave the way for the identification of potent Mab-SaS inhibitors, based on both established and unexplored chemotypes.

Treatment of non-tuberculosis mycobacteria skin infections

Non-tuberculosis mycobacteria (NTM) skin infections have become increasingly prevalent in recent years, presenting a unique challenge in clinical management. This review explored the complexities of NTM infections localized to the superficial tissues and provided valuable insights into the optimal therapeutic strategies. The antibiotic selection should base on NTM species and their susceptibility profiles. It is recommended to adopt a comprehensive approach that considers the unique characteristics of superficial tissues to improve treatment effectiveness and reduce the incidence of adverse reactions, infection recurrence, and treatment failure. Infection control measures, patient education, and close monitoring should complement the treatment strategies to achieve favorable outcomes in managing NTM skin infections. Further efforts are warranted to elucidate factors and mechanisms contributing to treatment resistance and relapse. Future research should focus on exploring novel treatment options, innovative drug development/delivery platforms, and precise methodologies for determining therapeutic duration. Longitudinal studies are also needed to assess the long-term safety profiles of the integrated approaches.

Epidemiology, management, and clinical outcomes of extrapulmonary Mycobacterium abscessus complex infections in heart transplant and ventricular assist device recipients

Nontuberculous mycobacteria are emerging pathogens, yet data on the epidemiology and management of extrapulmonary nontuberculous mycobacteria infections in orthotopic heart transplantation (OHT) and ventricular assist device (VAD) recipients are scarce. We retrospectively reviewed records of OHT and VAD recipients who underwent cardiac surgery at our hospital and developed Mycobacterium abscessus complex (MABC) infection from 2013 to 2016 during a hospital outbreak of MABC linked to heater-cooler units. We analyzed patient characteristics, medical and surgical management, and long-term outcomes. Ten OHT patients and 7 patients with VAD developed extrapulmonary M. abscessus subspecies abscessus infection. The median time from presumed inoculation during cardiac surgery to the first positive culture was 106 days in OHT and 29 days in VAD recipients. The most common sites of positive cultures were blood (n = 12), sternum/mediastinum (n = 8), and the VAD driveline exit site (n = 7). The 14 patients diagnosed when alive received combination antimicrobial therapy for a median of 21 weeks, developed 28 antibiotic-related adverse events, and underwent 27 surgeries. Only 8 (47%) patients survived longer than 12 weeks after diagnosis, including 2 patients with VAD who experienced long-term survival after an explantation of infected VADs and OHT. Despite aggressive medical and surgical management, OHT and VAD patients with MABC infection experienced substantial morbidity and mortality.

Preclinical murine models to study lung infection with Mycobacterium abscessus complex

Mycobacterium abscessus is a non-tuberculous mycobacterium (NTM) able to cause invasive pulmonary infections, named NTM pulmonary disease. The therapeutic approaches are limited, and infections are difficult to treat due to antibiotic resistance conferred by an impermeable cell wall, drug efflux pumps, or drug-modifying enzymes. The development of new therapeutics, intended as antimicrobials or drug limiting immunopathology, is urgently necessary. In this context, the preclinical murine models of M. abscessus represent a useful tool to validate and translate in vitro-proofed concepts. These in vivo models are essential for developing new targets and drugs, ameliorating our knowledge in combinatorial regimens of current existing antibiotic treatments, and repurposing existing drugs for new therapeutic options against M. abscessus infection. Thus, this review aims at providing an overview of the current state of the art of preclinical murine models to study M. abscessus lung infection and its exploitation for new therapeutic approaches. This review discusses the murine models available focusing on the different bacterial challenges (aerosol, intranasal, intratracheal, and intravenous administrations), murine genetic background, and additional bacterial related factors. Then, we discuss the successful preclinical models for M. abscessus respiratory infection exploited to study the efficacy and safety of new antimicrobials or to determine the best dosage and route of administration of existing drugs. Finally, we present the current murine models exploited to develop new therapeutic approaches to modulate the host immune response and limit immunopathological damage during M. abscessus lung disease. In conclusion, our review article provides an overview of current and available murine models to characterize acute or chronic infections and to study the outcome of new therapeutic strategies against M. abscessus lung infection.

Omadacycline for management of Mycobacterium abscessus infections: a review of its effectiveness, place in therapy, and considerations for use

The Mycobacterium abscessus complex (MABC) is a group of acid-fast, rapidly dividing non-tuberculous mycobacteria (NTM) that include a number of clinically important subspecies, including M. abscessus, M. bolletii, and M. massiliense. These organisms are prevalent in the environment and are primarily associated with human pulmonary or skin and skin structure infections (SSSI) but may cause more deep-seeded disseminated infections and bacteremia in the immunocompromised. Importantly, these NTM are resistant to most first-line anti-tuberculous agents and, due to intrinsic or acquired resistance, exhibit exceedingly low, variable, and geographically distinct susceptibilities to commonly used antibacterial agents including older tetracyclines, macrolides, aminoglycosides, cephalosporins, carbapenems, and sulfamethoxazole-trimethoprim. Omadacycline is a novel third-generation member of the tetracycline family of antibacterials that has recently been demonstrated to have potent anti-NTM effects and clinical efficacy against MABC, including M. abscessus. The purpose of this review is to present a comprehensive and up-to-date assessment on the body of literature on the role of omadacycline for M. abscessus infections. Specifically, the in vitro and in vivo microbiology, mechanisms of action, mechanisms of resistance, clinical pharmacokinetics, clinical efficacy, adverse effects, dosage and administration, and place in therapy of omadacycline in management of M. abscessus infections will be detailed.

Activity of Drug Combinations against Mycobacterium abscessus Grown in Aerobic and Hypoxic Conditions

Infections caused by Mycobacterium abscessus (Mab), an environmental non-tuberculous mycobacterium, are difficult to eradicate from patients with pulmonary diseases such as cystic fibrosis and bronchiectasis even after years of antibiotic treatments. In these people, the low oxygen pressure in mucus and biofilm may restrict Mab growth from actively replicating aerobic (A) to non-replicating hypoxic (H) stages, which are known to be extremely drug-tolerant. After the exposure of Mab A and H cells to drugs, killing was monitored by measuring colony-forming units (CFU) and regrowth in liquid medium (MGIT 960) of 1-day-old A cells (A1) and 5-day-old H cells (H5). Mab killing was defined as a lack of regrowth of drug-exposed cells in MGIT tubes after >50 days of incubation. Out of 18 drugs tested, 14-day treatments with bedaquiline-amikacin (BDQ-AMK)-containing three-drug combinations were very active against A1 + H5 cells. However, drug-tolerant cells (persisters) were not killed, as shown by CFU curves with typical bimodal trends. Instead, 56-day treatments with the nitrocompounds containing combinations BDQ-AMK-rifabutin-clarithromycin-nimorazole and BDQ-AMK-rifabutin-clarithromycin-metronidazole-colistin killed all A1 + H5 Mab cells in 42 and 56 days, respectively, as shown by lack of regrowth in agar and MGIT medium. Overall, these data indicated that Mab persisters may be killed by appropriate drug combinations.

Ethyl Acetate Fraction of Bixa orellana and Its Component Ellagic Acid Exert Antibacterial and Anti-Inflammatory Properties against Mycobacterium abscessus subsp. massiliense

Mycobacterium abscessus subsp. massiliense (Mabs) causes chronic infections, which has led to the need for new antimycobacterial agents. In this study, we investigated the antimycobacterial and anti-inflammatory activities of the ethyl acetate fraction of Bixa orellana leaves (BoEA) and ellagic acid (ElAc). In silico analysis predicted that ElAc had low toxicity, was not mutagenic or carcinogenic, and had antimicrobial and anti-inflammatory activities. Apparently, ElAc can interact with COX2 and Dihydrofolate reductase (DHFR) enzymes, which could explain both activities. In vitro analysis showed that BoEA and ElAc exerted antimicrobial activity against Mabs (minimum inhibitory concentration of 1.56, 1.56 mg/mL and bactericidal concentration of 6.25, 3.12 mg/mL, respectively. Clarithromycin showed MIC and MBC of 1 and 6 µg/mL). Treatment with BoEA or ElAc increased survival of Tenebrio molitor larvae after lethal infection with Mabs and reduced carrageenan-induced paw edema in mice, around 40% of edema volume after the fourth hour, similarly to diclofenac. In conclusion, BoEA and ElAc exert antimicrobial effects against Mabs and have anti-inflammatory effects, making them potential sources of antimycobacterial drugs. The biological activities of ElAc may be due to its high binding affinities predicted for COX2 and DHFR enzymes.

A Rare Insidious Case of Skin and Soft Tissue Infection Due to Mycobacterium abscessus: A Case Report

Mycobacterium abscessus complex (MABc) is part of the rapid-growing non-tuberculous mycobacteria group that usually resides in natural water sources. When it affects humans, it can be highly resistant and difficult to manage. The most common presentation is localized, mainly in the lungs and soft tissue, but can be generalized in immunocompromised patients. Here we present a case report of a 40-year-old female with a chronic infection of the abdominal wall after abdominoplasty.

Antibiotic susceptibility of mycobacteria isolated from ornamental fish

Introduction

Nontuberculous mycobacteria (NTM) are increasingly recognised as causative agents of opportunistic infections in humans for which effective treatment is challenging. There is very little information on the prevalence of NTM drug resistance in Poland. This study was aimed to evaluate the susceptibility to antibiotics of NTM, originally isolated from diseased ornamental fish.

Material and Methods

A total of 99 isolates were studied, 50 of them rapidly growing mycobacteria (RGM) (among which three-quarters were Mycobacterium chelonae, M. peregrinum, and M. fortuitum and the rest M. neoaurum, M. septicum, M. abscessus, M. mucogenicum, M. salmoniphilum, M saopaulense, and M. senegalense). The other 49 were slowly growing mycobacteria (SGM) isolates (among which only one was M. szulgai and the bulk M. marinum and M. gordonae). Minimum inhibitory concentrations for amikacin (AMK), kanamycin (KAN), tobramycin (TOB), doxycycline (DOX), ciprofloxacin (CIP), clarithromycin (CLR), sulfamethoxazole (SMX), isoniazid (INH) and rifampicin (RMP) were determined.

Results

The majority of the isolates were susceptible to KAN (95.95%: RGM 46.46% and SGM 49.49%), AMK (94.94%: RGM 45.45% and SGM 49.49%), CLR (83.83%: RGM 36.36% and SGM 47.47%), SMX (79.79%: RGM 30.30% and SMG 49.49%), CIP (65.65%: RGM 24.24% and SGM 41.41%), and DOX (55.55%: RGM 9.06% and SGM 46.46%). The majority were resistant to INH (98.98%: RGM 50.50% and SGM 48.48%) and RMP (96.96%: RGM 50.50% and SGM 46.46%).

Conclusion

The drug sensitivity of NTM varies from species to species. KAN, AMK, CLR and SMX were the most active against RGM isolates, and these same four plus DOX and CIP were the best drugs against SGM isolates.

Protective Efficacy of BCG Vaccine against Mycobacterium leprae and Non-Tuberculous Mycobacterial Infections

The genus mycobacterium includes several species that are known to cause infections in humans. The microorganisms are classified into tuberculous and non-tuberculous based on their morphological characteristics, defined by the dynamic relationship between the host defenses and the infectious agent. Non-tuberculous mycobacteria (NTM) include all the species of mycobacterium other than the ones that cause tuberculosis (TB). The group of NTM contains almost 200 different species and they are found in soil, water, animals—both domestic and wild—milk and food products, and from plumbed water resources such as sewers and showerhead sprays. A systematic review of Medline between 1946 and 2014 showed an 81% decline in TB incidence rates with a simultaneous 94% increase in infections caused by NTM. Prevalence of infections due to NTM has increased relative to infections caused by TB owing to the stringent prevention and control programs in Western countries such as the USA and Canada. While the spread of typical mycobacterial infections such as TB and leprosy involves human contact, NTM seem to spread easily from the environment without the risk of acquiring from a human contact except in the case of M. abscessus in patients with cystic fibrosis, where human transmission as well as transmission through fomites and aerosols has been recorded. NTM are opportunistic in their infectious processes, making immunocompromised individuals such as those with other systemic infections such as HIV, immunodeficiencies, pulmonary disease, or usage of medications such as long-term corticosteroids/TNF-α inhibitors more susceptible. This review provides insight on pathogenesis, treatment, and BCG vaccine efficacy against M. leprae and some important NTM infections.

Meeting the challenges of NTM-PD from the perspective of the organism and the disease process: innovations in drug development and delivery

Non-tuberculous mycobacterial pulmonary disease (NTM-PD) poses a substantial patient, healthcare, and economic burden. Managing NTM-PD remains challenging, and factors contributing to this include morphological, species, and patient characteristics as well as the treatment itself. This narrative review focusses on the challenges of NTM-PD from the perspective of the organism and the disease process. Morphological characteristics of non-tuberculous mycobacteria (NTM), antimicrobial resistance mechanisms, and an ability to evade host defences reduce NTM susceptibility to many antibiotics. Resistance to antibiotics, particularly macrolides, is of concern, and is associated with high mortality rates in patients with NTM-PD. New therapies are desperately needed to overcome these hurdles and improve treatment outcomes in NTM-PD. Amikacin liposome inhalation suspension (ALIS) is the first therapy specifically developed to treat refractory NTM-PD caused by Mycobacterium avium complex (MAC) and is approved in the US, EU and Japan. It provides targeted delivery to the lung and effective penetration of macrophages and biofilms and has demonstrated efficacy in treating refractory MAC pulmonary disease (MAC-PD) in the Phase III CONVERT study. Several other therapies are currently being developed including vaccination, bacteriophage therapy, and optimising host defences. Newly developed antibiotics have shown potential activity against NTM-PD and include benzimidazole, delamanid, and pretomanid. Antibiotics commonly used to treat other infections have also been repurposed for NTM-PD, including clofazimine and bedaquiline. Data from larger-scale studies are needed to determine the potential of many of these therapies for treating NTM-PD.

Pulmonary Mycobacterium abscessus Infection in an 11-Year-Old Child, Successfully Treated with Inhaled/Parenteral Amikacin: A Case Report and Review of Literature

Mycobacterium abscessus appears to be increasing cause of pulmonary infection in children with underlying risk factors including cystic fibrosis, chronic lung disease and immunodeficiency syndromes. We present a case of pulmonary M. abscessus infection in a pediatric patient with primary ciliary dyskinesia and he was successfully treated with parenteral amikacin, linezolid and oral clarithromycin combined with inhaled amikacin. Clinical improvement was observed after adding inhaled amikacin to the treatment.

β-Lactam Combinations That Exhibit Synergy against Mycobacteroides abscessus Clinical Isolates

Mycobacteroides abscessus (Mab) is an opportunistic environmental pathogen that can cause chronic pulmonary disease in the setting of structural lung conditions such as bronchiectasis, chronic obstructive pulmonary disease, and cystic fibrosis. These infections are often incurable and associated with rapid lung function decline. Mab is naturally resistant to most of the antibiotics available today, and current treatment guidelines require at least 1 year of daily multidrug therapy, which is often ineffective and is associated with significant toxicities. β-Lactams are the most widely used class of antibiotics and have a demonstrated record of safety and tolerability. Here, using a panel of recent clinical isolates of Mab, we evaluated the in vitro activities of dual-β-lactam combinations to identify new treatments with the potential to treat infections arising from a wide range of Mab strains. The Mab clinical isolates were heterogeneous, as reflected by the diversity of their genomes and differences in their susceptibilities to various drugs. Cefoxitin and imipenem are currently the only two β-lactams included in the guidelines for treating Mab disease, yet they are not used concurrently in clinical practice. However, this dual-β-lactam combination exhibited synergy against 100% of the isolates examined (n = 21). Equally surprising is the finding that the combination of two carbapenems, doripenem and imipenem, exhibited synergy against the majority of Mab isolates. In the setting of multidrug-resistant Mab disease with few therapeutic options, these combinations may offer viable immediate treatment options with efficacy against the broad spectrum of Mab strains infecting patients today.

Considerations for Phage Therapy Against Mycobacterium abscessus

There is a global increasing number of Mycobacterium abscessus infections, especially pulmonary infections. Reduced therapeutic options exist against this opportunistic pathogen due to its high intrinsic and acquired levels of antibiotic resistance. Phage therapy is a promising afresh therapy, which uses viruses to lyse bacteria responsible for the infection. Bacteriophages have been recently administered under compassionate use to a 15-year-old patient infected with M. abscessus in combination with antibiotics with excellent results. This mini review highlights different recommendations for future phage administrations such as where to look for new phages, the use of cocktail of mycobacteriophages to broaden phage specificity and to tackle resistance and phage insensitivity due to temperate phages present in bacterial genomes, the combined use of phages and antibiotics to obtain a synergistic effect, the liposomal administration to reach a prolonged effect, intracellular delivery and protection against neutralizing antibodies, and the convenience of using this strategy in patients suffering from cystic fibrosis (CF) since phages are believed to promote immunomodulatory actions and eliminate biofilms.