Mycobacteriophages to Treat Tuberculosis: Dream or Delusion?

Antibacterial efficacy of mycobacteriophages against virulent Mycobacterium tuberculosis

Tuberculosis (TB) remains a major global health concern, with drug-resistant strains posing a significant challenge to effective treatment. Bacteriophage (phage) therapy has emerged as a potential alternative to combat antibiotic resistance. In this study, we investigated the efficacy of widely used mycobacteriophages (D29, TM4, DS6A) against Mycobacterium tuberculosis (M. tuberculosis) under pathophysiological conditions associated with TB, such as low pH and hypoxia. We found that even at low multiplicity of infection (MOI), mycobacteriophages effectively infected M. tuberculosis, got rapidly amplified, and lysed M. tuberculosis, demonstrating their potential as therapeutic agents. Furthermore, we observed a novel phage tolerance mechanism with bacteria forming aggregates after several days of phage treatment. These aggregates were enriched with biofilm components and metabolically active bacteria. However, no phage tolerance was observed upon treatment with the three-phage mixture, highlighting the dynamic interplay between phages and bacteria and emphasizing the importance of phage cocktails. We also observed that phages were effective in lysing bacteria even under low pH and low oxygen concentrations as well as antibiotic-resistant bacteria. Our results provide key insights into phage infection of slow-growing bacteria and suggest that mycobacteriophages can effectively eliminate M. tuberculosis in complex pathophysiological environments like hypoxia and acidic pH. These results can aid in developing targeted phage-based therapies to combat antibiotic-resistant mycobacterial infections.

Preclinical murine models for the testing of antimicrobials against Mycobacterium abscessus pulmonary infections: Current practices and recommendations

Mycobacterium abscessus, a rapidly growing nontuberculous mycobacterium, is increasingly recognized as an important pathogen of the human lung, disproportionally affecting people with cystic fibrosis (CF) and other susceptible individuals with non-CF bronchiectasis and compromised immune functions. M. abscessus infections are extremely difficult to treat due to intrinsic resistance to many antibiotics, including most anti-tuberculous drugs. Current standard-of-care chemotherapy is long, includes multiple oral and parenteral repurposed drugs, and is associated with significant toxicity. The development of more effective oral antibiotics to treat M. abscessus infections has thus emerged as a high priority. While murine models have proven instrumental in predicting the efficacy of therapeutic treatments for M. tuberculosis infections, the preclinical evaluation of drugs against M. abscessus infections has proven more challenging due to the difficulty of establishing a progressive, sustained, pulmonary infection with this pathogen in mice. To address this issue, a series of three workshops were hosted in 2023 by the Cystic Fibrosis Foundation (CFF) and the National Institute of Allergy and Infectious Diseases (NIAID) to review the current murine models of M. abscessus infections, discuss current challenges and identify priorities toward establishing validated and globally harmonized preclinical models. This paper summarizes the key points from these workshops. The hope is that the recommendations that emerged from this exercise will facilitate the implementation of informative murine models of therapeutic efficacy testing across laboratories, improve reproducibility from lab-to-lab and accelerate preclinical-to-clinical translation.

Mycobacteriophages: therapeutic approach for mycobacterial infections

Tuberculosis (TB) is a significant global health threat, and cases of infection with non-tuberculous mycobacteria (NTM) causing lung disease (NTM-LD) are rising. Bacteriophages and their gene products have garnered interest as potential therapeutic options for bacterial infections. Here, we have compiled information on bacteriophages and their products that can kill Mycobacterium tuberculosis or NTM. We summarize the mechanisms whereby viable phages can access macrophage-resident bacteria and not elicit immune responses, review methodologies of pharmaceutical product development containing mycobacteriophages and their gene products, mainly lysins, in the context of drug regulatory requirements and we discuss industrially relevant methods for producing pharmaceutical products comprising mycobacteriophages, emphasizing delivery of mycobacteriophages to the lungs. We conclude with an outline of some recent case studies on mycobacteriophage therapy.

Mycobacteriophage D29 Lysin B exhibits promising anti-mycobacterial activity against drug-resistant Mycobacterium tuberculosis

IMPORTANCE

To combat the rapidly emerging drug-resistant M. tuberculosis, it is now essential to look for alternative therapeutics. Mycobacteriophages can be considered as efficient therapeutics due to their natural ability to infect and kill mycobacteria including M. tuberculosis. Here, we have exploited the mycolyl-arabinogalactan esterase property of LysB encoded from mycobacteriophage D29. This study is novel in terms of targeting a multi-drug-resistant pathogenic strain of M. tuberculosis with LysB and also examining the combination of anti-TB drugs and LysB. All the experiments include external administration of LysB. Therefore, the remarkable lytic activity of LysB overcomes the difficulty to enter the complex cell envelope of mycobacteria. Targeting the intracellularly located M. tuberculosis by LysB and non-toxicity to macrophages take the process of the development of LysB as a drug one step ahead, and also, the interaction studies with rifampicin and isoniazid will help to form a new treatment regimen against tuberculosis.

Mycobacteriophages in diagnosis and alternative treatment of mycobacterial infections

Antimicrobial resistance is an increasing threat to human populations. The emergence of multidrug-resistant "superbugs" in mycobacterial infections has further complicated the processes of curing patients, thereby resulting in high morbidity and mortality. Early diagnosis and alternative treatment are important for improving the success and cure rates associated with mycobacterial infections and the use of mycobacteriophages is a potentially good option. Since each bacteriophage has its own host range, mycobacteriophages have the capacity to detect specific mycobacterial isolates. The bacteriolysis properties of mycobacteriophages make them more attractive when it comes to treating infectious diseases. In fact, they have been clinically applied in Eastern Europe for several decades. Therefore, mycobacteriophages can also treat mycobacteria infections. This review explores the potential clinical applications of mycobacteriophages, including phage-based diagnosis and phage therapy in mycobacterial infections. Furthermore, this review summarizes the current difficulties in phage therapy, providing insights into new treatment strategies against drug-resistant mycobacteria.

Functional Whole Genome Screen of Nutrient-Starved Mycobacterium tuberculosis Identifies Genes Involved in Rifampin Tolerance

Mycobacterium tuberculosis (Mtb), the causative agent of tuberculosis (TB), poses a global health challenge and is responsible for over a million deaths each year. Current treatment is lengthy and complex, and new, abbreviated regimens are urgently needed. Mtb adapts to nutrient starvation, a condition experienced during host infection, by shifting its metabolism and becoming tolerant to the killing activity of bactericidal antibiotics. An improved understanding of the mechanisms mediating antibiotic tolerance in Mtb can serve as the basis for developing more effective therapies. We performed a forward genetic screen to identify candidate Mtb genes involved in tolerance to the two key first-line antibiotics, rifampin and isoniazid, under nutrient-rich and nutrient-starved conditions. In nutrient-rich conditions, we found 220 mutants with differential antibiotic susceptibility (218 in the rifampin screen and 2 in the isoniazid screen). Following Mtb adaptation to nutrient starvation, 82 mutants showed differential antibiotic susceptibility (80 in the rifampin screen and 2 in the isoniazid screen). Using targeted mutagenesis, we validated the rifampin-hypersusceptible phenotype under nutrient starvation in Mtb mutants lacking the following genes: ercc3, moeA1, rv0049, and rv2179c. These findings shed light on potential therapeutic targets, which could help shorten the duration and complexity of antitubercular regimens.

New advances in the treatments of drug-resistant tuberculosis

INTRODUCTION

TB is associated with high mortality and morbidity among infected individuals and a high transmission rate from person to person. Despite the availability of vaccines and several anti-TB,TB infection continues to increase. Global resistance to TB remains the greatest challenge. There has not been extensive research into a new treatment and management strategy for TB resistance therapy. This review is based on a review of new advances and alternative drugs in the treatment of drug-resistant TB.

AREAS COVERED

New drug-resistant Mycobacterium tuberculosis therapy involves a combination of the latest TB drugs, new anti-TB drugs based on medicinal plant extracts for drug-resistant TB, mycobacteriophage therapy, the CRISPR/Cas9 system, and nanotechnology.

EXPERT OPINION

It is necessary to determine the function of individual gene alterations in drug-resistant TB. A combination of the most recent anti-TB drugs, such as bedaquiline and delamanid, is recommended. Longitudinal studies and animal model experiments with some medicinal plant extracts are required for better results. Nanotechnology has the potential to reduce drug side effects. Useful efficacy of phage therapy and CRISPR-cas9 technology as adjunct therapies for the management of drug-resistant TB.

Experimental Studies of the Liposomal Form of Lytic Mycobacteriophage D29 for the Treatment of Tuberculosis Infection

We have studied the antimycobacterial efficacy of the liposomal preparation of mycobacteriophage D29 on models of tuberculous granuloma in vitro and in the experiment on laboratory mice of the relatively resistant strain C57BL/6, infected with the virulent strain of M. tuberculosis H37Rv. We have shown the preparation of liposomal preparation of the lytic mycobacteriophages and its characteristics. The experiments showed a significant lytic effect of the liposomal form of mycobacteriophage D29 both on the model of tuberculous granuloma formed by human blood mononuclear cells in vitro, which is formed in the presence of Mycobacterium tuberculosis and on the model of tuberculous infection in C57BL/6 mice. Keywords: mycobacteriophage D29, M. tuberculosis, liposomes, tuberculous granuloma in vitro, tuberculosis infection and its treatment.

A structural dendrogram of the actinobacteriophage major capsid proteins provides important structural insights into the evolution of capsid stability

Many double-stranded DNA viruses, including tailed bacteriophages (phages) and herpesviruses, use the HK97-fold in their major capsid protein to make the capsomers of the icosahedral viral capsid. After the genome packaging at near-crystalline densities, the capsid is subjected to a major expansion and stabilization step that allows it to withstand environmental stresses and internal high pressure. Several different mechanisms for stabilizing the capsid have been structurally characterized, but how these mechanisms have evolved is still not understood. Using cryo-EM structure determination of 10 capsids, structural comparisons, phylogenetic analyses, and Alphafold predictions, we have constructed a detailed structural dendrogram describing the evolution of capsid structural stability within the actinobacteriophages. We show that the actinobacteriophage major capsid proteins can be classified into 15 groups based upon their HK97-fold.

Phage Therapy for Nontuberculous Mycobacteria: Challenges and Opportunities

Non-tuberculous mycobacterium (NTM) infections are often clinically challenging, with lengthy antibiotic regimens that fail to resolve the infections with few good outcomes remaining. Mycobacteriophages-viruses that infect Mycobacterium hosts-show promise as therapeutic agents for NTM infections and have been used in 20 compassionate use cases. Favorable outcomes were observed in many but not all cases, although the phages show exceptional safety profiles and no evidence of phage resistance was observed, even when only a single phage was administered. Phage-specific antibodies are commonly present following intravenous administration and are often neutralizing for the phage in vitro. However, phage neutralization does not consistently correlate with poor treatment outcomes and may not be a therapeutic limitation in all patients, even when immunocompetent. Currently, the therapeutic potential of phages is substantially limited by the great variation in phage susceptibility and a relatively small repertoire of therapeutically useful phages. As many as 45% of clinical isolates can have a smooth colony morphotype, and phages that both efficiently infect and kill these strains have yet to be described. In contrast, ~ 75% of rough strains are susceptible to and killed by one or more phages and therapeutic options can be considered on a compassionate use basis. Although therapies must currently be personalized, elucidating the determinants of phage host specificity, expanding the useful phage repertoire, and identifying the key determinants of clinical outcomes will reveal their full therapeutic potential.

Complete Genome Sequence of Finnry, a Subcluster L3 Mycobacteriophage from Charleston, South Carolina

Subcluster L3 bacteriophage Finnry was isolated from soil collected in Charleston, South Carolina, using Mycobacterium smegmatis mc 2 155 as a host. The genome of this temperate siphovirus is 75,632 bp long (130 predicted protein-coding genes, 9 tRNAs, and no transfer-messenger RNAs), and BLASTn alignment revealed 99.86% identity with the genome of L3 mycobacteriophage Samty.

Mycobacteriophages: From Petri dish to patient

Mycobacteriophages-bacteriophages infecting Mycobacterium hosts-contribute substantially to our understanding of viral diversity and evolution, provide resources for advancing Mycobacterium genetics, are the basis of high-impact science education programs, and show considerable therapeutic potential. Over 10,000 individual mycobacteriophages have been isolated by high school and undergraduate students using the model organism Mycobacterium smegmatis mc2155 and 2,100 have been completely sequenced, giving a high-resolution view of the phages that infect a single common host strain. The phage genomes are revealed to be highly diverse and architecturally mosaic and are replete with genes of unknown function. Mycobacteriophages have provided many widely used tools for Mycobacterium genetics including integration-proficient vectors and recombineering systems, as well as systems for efficient delivery of reporter genes, transposons, and allelic exchange substrates. The genomic insights and engineering tools have facilitated exploration of phages for treatment of Mycobacterium infections, although their full therapeutic potential has yet to be realized.