Aerosol phage therapy efficacy in Burkholderia cepacia complex respiratory infections

Identification and Characterization of Type IV Pili as the Cellular Receptor of Broad Host Range Stenotrophomonas maltophilia Bacteriophages DLP1 and DLP2

Bacteriophages DLP1 and DLP2 are capable of infecting both Stenotrophomonas maltophilia and Pseudomonas aeruginosa strains, two highly antibiotic resistant bacterial pathogens, which is unusual for phages that typically exhibit extremely limited host range. To explain their unusual cross-order infectivity and differences in host range, we have identified the type IV pilus as the primary receptor for attachment. Screening of a P. aeruginosa PA01 mutant library, a host that is susceptible to DLP1 but not DLP2, identified DLP1-resistant mutants with disruptions in pilus structural and regulatory components. Subsequent complementation of the disrupted pilin subunit genes in PA01 restored DLP1 infection. Clean deletion of the major pilin subunit, pilA, in S. maltophilia strains D1585 and 280 prevented phage binding and lysis by both DLP1 and DLP2, and complementation restored infection by both. Transmission electron microscopy shows a clear interaction between DLP1 and pili of both D1585 and PA01. These results support the identity of the type IV pilus as the receptor for DLP1 and DLP2 infection across their broad host ranges. This research further characterizes DLP1 and DLP2 as potential “anti-virulence” phage therapy candidates for the treatment of multidrug resistant bacteria from multiple genera.

Effect of storage temperature on the stability of spray dried bacteriophage powders

This study aimed to assess the robustness of using a spray drying approach and formulation design in producing inhalable phage powders. Two types of Pseudomonas phages, PEV2 (Podovirus) and PEV40 (Myovirus) in two formulations containing different amounts of trehalose (70% and 60%) and leucine (30% and 40%) were studied. Most of the surface of the produced powders was found to be covered in crystalline leucine. The powders were stored at 4 °C and 20 °C under vacuum. The phage stability and in vitro aerosol performance of the phage powders were examined on the day of production and after 1, 3 and 12 months of storage. A minor titer loss during production was observed for both phages (0.2-0.8 log10 pfu/ml). The storage stability of the produced phage powders was found to be phage and formulation dependent. No further reduction in titer occurred for PEV2 powders stored at 4 °C across the study. The formulation containing 30% leucine maintained the viability of PEV2 at 20 °C, while the formulation containing 40% leucine gradually lost titer over time with a storage reduction of ∼0.9 log10 pfu/ml measured after 12 months. In comparison, the PEV40 phage powders generally had a ∼ 0.5 log10 pfu/ml loss upon storage regardless of temperature. When aerosolized, the total in vitro lung doses of PEV2 were of the order of 107 pfu, except the formulation containing 40% leucine stored at 20 °C which had a lower lung dose. The PEV40 powders also had lung doses of 106-107 pfu. The results demonstrate that spray dried Myoviridae and Podoviridae phage in a simple formulation of leucine and trehalose can be successfully stored for one year at 4 °C and 20 °C with vacuum packaging.

Formulation, stabilisation and encapsulation of bacteriophage for phage therapy

Against a backdrop of global antibiotic resistance and increasing awareness of the importance of the human microbiota, there has been resurgent interest in the potential use of bacteriophages for therapeutic purposes, known as phage therapy. A number of phage therapy phase I and II clinical trials have concluded, and shown phages don't present significant adverse safety concerns. These clinical trials used simple phage suspensions without any formulation and phage stability was of secondary concern. Phages have a limited stability in solution, and undergo a significant drop in phage titre during processing and storage which is unacceptable if phages are to become regulated pharmaceuticals, where stable dosage and well defined pharmacokinetics and pharmacodynamics are de rigueur. Animal studies have shown that the efficacy of phage therapy outcomes depend on the phage concentration (i.e. the dose) delivered at the site of infection, and their ability to target and kill bacteria, arresting bacterial growth and clearing the infection. In addition, in vitro and animal studies have shown the importance of using phage cocktails rather than single phage preparations to achieve better therapy outcomes. The in vivo reduction of phage concentration due to interactions with host antibodies or other clearance mechanisms may necessitate repeated dosing of phages, or sustained release approaches. Modelling of phage-bacterium population dynamics reinforces these points. Surprisingly little attention has been devoted to the effect of formulation on phage therapy outcomes, given the need for phage cocktails, where each phage within a cocktail may require significantly different formulation to retain a high enough infective dose. This review firstly looks at the clinical needs and challenges (informed through a review of key animal studies evaluating phage therapy) associated with treatment of acute and chronic infections and the drivers for phage encapsulation. An important driver for formulation and encapsulation is shelf life and storage of phage to ensure reproducible dosages. Other drivers include formulation of phage for encapsulation in micro- and nanoparticles for effective delivery, encapsulation in stimuli responsive systems for triggered controlled or sustained release at the targeted site of infection. Encapsulation of phage (e.g. in liposomes) may also be used to increase the circulation time of phage for treating systemic infections, for prophylactic treatment or to treat intracellular infections. We then proceed to document approaches used in the published literature on the formulation and stabilisation of phage for storage and encapsulation of bacteriophage in micro- and nanostructured materials using freeze drying (lyophilization), spray drying, in emulsions e.g. ointments, polymeric microparticles, nanoparticles and liposomes. As phage therapy moves forward towards Phase III clinical trials, the review concludes by looking at promising new approaches for micro- and nanoencapsulation of phages and how these may address gaps in the field.

Burkholderia cenocepacia Infections in Cystic Fibrosis Patients: Drug Resistance and Therapeutic Approaches

Burkholderia cenocepacia is an opportunistic pathogen particularly dangerous for cystic fibrosis (CF) patients. It can cause a severe decline in CF lung function possibly developing into a life-threatening systemic infection known as cepacia syndrome. Antibiotic resistance and presence of numerous virulence determinants in the genome make B. cenocepacia extremely difficult to treat. Better understanding of its resistance profiles and mechanisms is crucial to improve management of these infections. Here, we present the clinical distribution of B. cenocepacia described in the last 6 years and methods for identification and classification of epidemic strains. We also detail new antibiotics, clinical trials, and alternative approaches reported in the literature in the last 5 years to tackle B. cenocepacia resistance issue. All together these findings point out the urgent need of new and alternative therapies to improve CF patients’ life expectancy.

The potential of phage therapy in cystic fibrosis: Essential human-bacterial-phage interactions and delivery considerations for use in Pseudomonas aeruginosa-infected airways

As antimicrobial-resistant microbes become increasingly common and a significant global issue, novel approaches to treating these infections particularly in those at high risk are required. This is evident in people with cystic fibrosis (CF), who suffer from chronic airway infection caused by antibiotic resistant bacteria, typically Pseudomonas aeruginosa. One option is bacteriophage (phage) therapy, which utilises the natural predation of phage viruses upon their host bacteria. This review summarises the essential and unique aspects of the phage-microbe-human lung interactions in CF that must be addressed to successfully develop and deliver phage to CF airways. The current evidence regarding phage biology, phage-bacterial interactions, potential airway immune responses to phages, previous use of phages in humans and method of phage delivery to the lung are also summarised.

Recent advances in therapeutic delivery systems of bacteriophage and bacteriophage-encoded endolysins

Antibiotics have been the cornerstone of clinical management of bacterial infection since their discovery in the early 20th century. However, their widespread and often indiscriminate use has now led to reports of multidrug resistance becoming globally commonplace. Bacteriophage therapy has undergone a recent revival in battle against pathogenic bacteria, as the self-replicating and co-evolutionary features of these predatory virions offer several advantages over conventional therapeutic agents. In particular, the use of targeted bacteriophage therapy from specialized delivery platforms has shown particular promise owing to the control of delivery location, administration conditions and dosage of the therapeutic cargo. This review presents an overview of the recent formulations and applications of such delivery vehicles as an innovative and elegant tool for bacterial control.

Anti-Tuberculosis Bacteriophage D29 Delivery with a Vibrating Mesh Nebulizer, Jet Nebulizer, and Soft Mist Inhaler

PURPOSE

To compare titer reduction and delivery rate of active anti-tuberculosis bacteriophage (phage) D29 with three inhalation devices.

METHODS

Phage D29 lysate was amplified to a titer of 11.8 ± 0.3 log₁₀(pfu/mL) and diluted 1:100 in isotonic saline. Filters captured the aerosolized saline D29 preparation emitted from three types of inhalation devices: 1) vibrating mesh nebulizer; 2) jet nebulizer; 3) soft mist inhaler. Full-plate plaque assays, performed in triplicate at multiple dilution levels with the surrogate host Mycobacterium smegmatis, were used to quantify phage titer.

RESULTS

Respective titer reductions for the vibrating mesh nebulizer, jet nebulizer, and soft mist inhaler were 0.4 ± 0.1, 3.7 ± 0.1, and 0.6 ± 0.3 log₁₀(pfu/mL). Active phage delivery rate was significantly greater (p < 0.01) for the vibrating mesh nebulizer (3.3x10⁸ ± 0.8x10⁸ pfu/min) than for the jet nebulizer (5.4x10⁴ ± 1.3x10⁴ pfu/min). The soft mist inhaler delivered 4.6x10⁶ ± 2.0x10⁶ pfu per 11.6 ± 1.6 μL ex-actuator dose.

CONCLUSIONS

Delivering active phage requires a prudent choice of inhalation device. The jet nebulizer was not a good choice for aerosolizing phage D29 under the tested conditions, due to substantial titer reduction likely occurring during droplet production. The vibrating mesh nebulizer is recommended for animal inhalation studies requiring large amounts of D29 aerosol, whereas the soft mist inhaler may be useful for self-administration of D29 aerosol.

Optimization and characterization of a murine lung infection model for the evaluation of novel therapeutics against Burkholderia cenocepacia

Several B. cenocepacia mouse models are available to study the pulmonary infection by this Burkholderia cepacia complex (BCC) species. However, a characterized B. cenocepacia mouse model to evaluate the efficacy of potential new antibacterial therapies is not yet described. Therefore, we optimized and validated the course of infection (i.e. bacterial proliferation in lung, liver and spleen) and the efficacy of a reference antibiotic, tobramycin (TOB), in a mouse lung infection model. Furthermore, the local immune response and histological changes in lung tissue were studied during infection and treatment. A reproducible lung infection was observed when immunosuppressed BALB/c mice were infected with B. cenocepacia LMG 16656. Approximately 50 to 60% of mice infected with this BCC species demonstrated a dissemination to liver and spleen. TOB treatment resulted in a two log reduction in lung burden, prevented dissemination of B. cenocepacia to liver and spleen and significantly reduced levels of proinflammatory cytokines. As this mouse model is characterized by a reproducible course of infection and efficacy of TOB, it can be used as a tool for the in vivo evaluation of new antibacterial therapies.

The isolation and characterization of Stenotrophomonas maltophilia T4-like bacteriophage DLP6

Increasing isolation of the extremely antibiotic resistant bacterium Stenotrophomonas maltophilia has caused alarm worldwide due to the limited treatment options available. A potential treatment option for fighting this bacterium is ‘phage therapy’, the clinical application of bacteriophages to selectively kill bacteria. Bacteriophage DLP6 (vB_SmoM-DLP6) was isolated from a soil sample using clinical isolate S. maltophilia strain D1571 as host. Host range analysis of phage DLP6 against 27 clinical S. maltophilia isolates shows successful infection and lysis in 13 of the 27 isolates tested. Transmission electron microscopy of DLP6 indicates that it is a member of the Myoviridae family. Complete genome sequencing and analysis of DLP6 reveals its richly recombined evolutionary history, featuring a core of both T4-like and cyanophage genes, which suggests that it is a member of the T4-superfamily. Unlike other T4-superfamily phages however, DLP6 features a transposase and ends with 229 bp direct terminal repeats. The isolation of this bacteriophage is an exciting discovery due to the divergent nature of DLP6 in relation to the T4-superfamily of phages.

Effects of storage conditions on the stability of spray dried, inhalable bacteriophage powders

This study aimed to develop inhalable powders containing phages active against antibiotic-resistant Pseudomonas aeruginosa for pulmonary delivery. A Pseudomonas phage, PEV2, was spray dried into powder matrices comprising of trehalose (0-80%), mannitol (0-80%) and l-leucine (20%). The resulting powders were stored at various relative humidity (RH) conditions (0, 22 and 60% RH) at 4°C. The phage stability and in vitro aerosol performance of the phage powders were examined at the time of production and after 1, 3 and 12 months storage. After spray drying, a total of 1.3 log titer reduction in phage was observed in the formulations containing 40%, 60% and 80% trehalose, whereas 2.4 and 5.1 log reductions were noted in the formulations containing 20% and no trehalose, respectively. No further reduction in titer occurred for powders stored at 0 and 22% RH even after 12 months, except the formulation containing no trehalose. The 60% RH storage condition had a destructive effect such that no viable phages were detected after 3 and 12 months. When aerosolised, the total lung doses for formulations containing 40%, 60% and 80% trehalose were similar (in the order of 10⁵ pfu). The results demonstrated that spray drying is a suitable method to produce stable phage powders for pulmonary delivery. A powder matrix containing ≥40% trehalose provided good phage preservation and aerosol performances after storage at 0 and 22% RH at 4°C for 12 months.

Control of Multidrug-Resistant Gene Flow in the Environment Through Bacteriophage Intervention

The spread of multidrug-resistant (MDR) bacteria is an emerging threat to the environment and public wellness. Inappropriate use and indiscriminate release of antibiotics in the environment through un-metabolized form create a scenario for the emergence of virulent pathogens and MDR bugs in the surroundings. Mechanisms underlying the spread of resistance include horizontal and vertical gene transfers causing the transmittance of MDR genes packed in different host, which pass across different food webs. Several controlling agents have been used for combating pathogens; however, the use of lytic bacteriophages proves to be one of the most eco-friendly due to their specificity, killing only target bacteria without damaging the indigenous beneficial flora of the habitat. Phages are part of the natural microflora present in different environmental niches and are remarkably stable in the environment. Diverse range of phage products, such as phage enzymes, phage peptides having antimicrobial properties, and phage cocktails also have been used to eradicate pathogens along with whole phages. Recently, the ability of phages to control pathogens has extended from the different areas of medicine, agriculture, aquaculture, food industry, and into the environment. To avoid the arrival of pre-antibiotic epoch, phage intervention proves to be a potential option to eradicate harmful pathogens generated by the MDR gene flow which are uneasy to cure by conventional treatments.

Identification of Diverse Mycoviruses through Metatranscriptomics Characterization of the Viromes of Five Major Fungal Plant Pathogens

Mycoviruses can have a marked effect on natural fungal communities and influence plant health and productivity. However, a comprehensive picture of mycoviral diversity is still lacking. To characterize the viromes of five widely dispersed plant-pathogenic fungi, Colletotrichum truncatum, Macrophomina phaseolina, Diaporthe longicolla, Rhizoctonia solani, and Sclerotinia sclerotiorum, a high-throughput sequencing-based metatranscriptomic approach was used to detect viral sequences. Total RNA and double-stranded RNA (dsRNA) from mycelia and RNA from samples enriched for virus particles were sequenced. Sequence data were assembled de novo, and contigs with predicted amino acid sequence similarities to viruses in the nonredundant protein database were selected. The analysis identified 72 partial or complete genome segments representing 66 previously undescribed mycoviruses. Using primers specific for each viral contig, at least one fungal isolate was identified that contained each virus. The novel mycoviruses showed affinity with 15 distinct lineages: Barnaviridae, Benyviridae, Chrysoviridae, Endornaviridae, Fusariviridae, Hypoviridae, Mononegavirales, Narnaviridae, Ophioviridae, Ourmiavirus, Partitiviridae, Tombusviridae, Totiviridae, Tymoviridae, and Virgaviridae More than half of the viral sequences were predicted to be members of the Mitovirus genus in the family Narnaviridae, which replicate within mitochondria. Five viral sequences showed strong affinity with three families (Benyviridae, Ophioviridae, and Virgaviridae) that previously contained no mycovirus species. The genomic information provides insight into the diversity and taxonomy of mycoviruses and coevolution of mycoviruses and their fungal hosts.

IMPORTANCE

Plant-pathogenic fungi reduce crop yields, which affects food security worldwide. Plant host resistance is considered a sustainable disease management option but may often be incomplete or lacking for some crops to certain fungal pathogens or strains. In addition, the rising issues of fungicide resistance demand alternative strategies to reduce the negative impacts of fungal pathogens. Those fungus-infecting viruses (mycoviruses) that attenuate fungal virulence may be welcome additions for mitigation of plant diseases. By high-throughput sequencing of the RNAs from 275 isolates of five fungal plant pathogens, 66 previously undescribed mycoviruses were identified. In addition to identifying new potential biological control agents, these results expand the grand view of the diversity of mycoviruses and provide possible insights into the importance of intracellular and extracellular transmission in fungus-virus coevolution.

Experimental Phage Therapy for Burkholderia pseudomallei Infection

Burkholderia pseudomallei is an intracellular Gram-negative bacterial pathogen intrinsically resistant to a variety of antibiotics. Phages have been developed for use as an alternative treatment therapy, particularly for bacterial infections that do not respond to conventional antibiotics. In this study, we investigated the use of phages to treat cells infected with B. pseudomallei. Phage C34 isolated from seawater was purified and characterised on the basis of its host range and morphology using transmission electron microscopy (TEM). Phage C34 was able to lyse 39.5% of B. pseudomallei clinical strains. Due to the presence of contractile tail, phage C34 is classified as a member of the family Myoviridae, a tailed double-stranded DNA virus. When 2 × 10⁵ A549 cells were exposed to 2 × 10⁷ PFU of phage C34, 24 hours prior to infection with 2 × 10⁶ CFU of B. pseudomallei, it was found that the survivability of the cells increased to 41.6 ± 6.8% as compared to 22.8 ± 6.0% in untreated control. Additionally, application of phage successfully rescued 33.3% of mice infected with B. pseudomallei and significantly reduced the bacterial load in the spleen of the phage-treated mice. These findings indicate that phage can be a potential antimicrobial agent for B. pseudomallei infections.

Production of Inhalation Phage Powders Using Spray Freeze Drying and Spray Drying Techniques for Treatment of Respiratory Infections

PURPOSE

The potential of aerosol phage therapy for treating lung infections has been demonstrated in animal models and clinical studies. This work compared the performance of two dry powder formation techniques, spray freeze drying (SFD) and spray drying (SD), in producing inhalable phage powders.

METHOD

A Pseudomonas podoviridae phage, PEV2, was incorporated into multi-component formulation systems consisting of trehalose, mannitol and L-leucine (F1 = 60:20:20 and F2 = 40:40:20). The phage titer loss after the SFD and SD processes and in vitro aerosol performance of the produced powders were assessed.

RESULTS

A significant titer loss (~2 log) was noted for droplet generation using an ultrasonic nozzle employed in the SFD method, but the conventional two-fluid nozzle used in the SD method was less destructive for the phage (~0.75 log loss). The phage were more vulnerable during the evaporative drying process (~0.75 log further loss) compared with the freeze drying step, which caused negligible phage loss. In vitro aerosol performance showed that the SFD powders (~80% phage recovery) provided better phage protection than the SD powders (~20% phage recovery) during the aerosolization process. Despite this, higher total lung doses were obtained for the SD formulations (SD-F1 = 13.1 ± 1.7 × 10(4) pfu and SD-F2 = 11.0 ± 1.4 × 10(4) pfu) than from their counterpart SFD formulations (SFD-F1 = 8.3 ± 1.8 × 10(4) pfu and SFD-F2 = 2.1 ± 0.3 × 10(4) pfu).

CONCLUSION

Overall, the SD method caused less phage reduction during the powder formation process and the resulted powders achieved better aerosol performance for PEV2.

Inhalation Study of Mycobacteriophage D29 Aerosol for Mice by Endotracheal Route and Nose-Only Exposure

BACKGROUND

Lytic mycobacteriophage D29 has the potential for tuberculosis treatment including multidrug-resistant strains. The aims of this study are to investigate deposition and distribution of aerosolized phage D29 particles in naive Balb/C mice, together with pharmacokinetics and evaluation of acute lung injury.

METHODS

Pharmacokinetics and BALF (bronchoalveolar lavage fluids) were analyzed after administration of phage D29 aerosols by endotracheal route using Penn-century aerosolizer; Collison 6-jet and Spinning top aerosol nebulizers (STAG) were used to generate phage aerosols with different particle size distributions in nose-only inhalation experiments. After exposure, deposited amounts of phage D29 particles in respiratory tracts were measured, and deposition efficiencies were calculated. A typical path deposition model for mice was developed, and then comparisons were made between predictions and experimentally measured results.

RESULTS

Approximately 10% of aerosolized phages D29 reached lung of mouse for pulmonary delivery, and were completely eliminated until 72 h after administration. In contrast, about 0.1% of intraperitoneal injected phages reached the lung, and were almost eliminated at 12 h time point. The inflammation was hardly observed in lung according to the results of BALF analysis. The CMADs (count median aerodynamic diameters) of generated aerosol by Collison and STAG nebulizer were 0.8 μm and 1.5 μm, respectively. After nose-only exposure, measured deposition efficiencies in whole respiratory tract for 0.8 and 1.5 μm phage particles were below 1% and 10%, respectively. Predictions of the computer deposition model compared fairly well with experimentally measured results.

CONCLUSIONS

This is the first systematic study of phage D29 aerosol respiratory challenge in laboratory animals. It provides evidence that aerosol delivery of phage D29 is an effective way for treating pulmonary infections caused by Mycobacterium tuberculosis. This research will also provide important data for future inhalation experiments.

Nanotechnological applications for the control of pulmonary infections

Pulmonary infections are the major global problem. According to the global burden of disease study, lower respiratory infections were ranked third among the leading causes of death after ischaemic heart disease and cerebrovascular disease. Despite the availability of treatment options and diagnostic methods, the severity of pulmonary infections is increasing due to the emergence of multiple drug resistance and lack of sensitivity in pathogenic microbes.

In this context, nanotechnology based treatment therapies have emerged as a promising approach to circumvent the limitations of conventional therapies and also manage the problem of drug resistance in pulmonary infections. The present chapter is focused on the global status of existing management strategies of pulmonary infections and their limitations. Moreover, the role of nanotechnology for the management of pulmonary infections with a special reference to different type of nanomaterials has also been discussed.

The Canadian Institutes of Health Research response to antimicrobial resistance

Antimicrobial resistance (AMR) has been a research priority for the Canadian Institutes of Health Research (CIHR), Institute of Infection and Immunity (III) since its inception, and a number of strategic research initiatives have been launched to address this global health problem by promoting and supporting research related to mechanisms and processes that impact the emergence and spread of resistance among individuals and within the environment. Here we will present research initiatives on AMR led by CIHR-III, which include national programs as well as international partnerships with the United Kingdom and the European Union, in addition to interesting outcomes of these initiatives.

The isolation and characterization of two Stenotrophomonas maltophilia bacteriophages capable of cross-taxonomic order infectivity

BACKGROUND

A rapid worldwide increase in the number of human infections caused by the extremely antibiotic resistant bacterium Stenotrophomonas maltophilia is prompting alarm. One potential treatment solution to the current antibiotic resistance dilemma is "phage therapy", the clinical application of bacteriophages to selectively kill bacteria.

RESULTS

Towards that end, phages DLP1 and DLP2 (vB_SmaS-DLP_1 and vB_SmaS-DLP_2, respectively) were isolated against S. maltophilia strain D1585. Host range analysis for each phage was conducted using 27 clinical S. maltophilia isolates and 11 Pseudomonas aeruginosa strains. Both phages exhibit unusually broad host ranges capable of infecting bacteria across taxonomic orders. Transmission electron microscopy of the phage DLP1 and DLP2 morphology reveals that they belong to the Siphoviridae family of bacteriophages. Restriction fragment length polymorphism analysis and complete genome sequencing and analysis indicates that phages DLP1 and DLP2 are closely related but different phages, sharing 96.7 % identity over 97.2 % of their genomes. These two phages are also related to P. aeruginosa phages vB_Pae-Kakheti_25 (PA25), PA73, and vB_PaeS_SCH_Ab26 (Ab26) and more distantly related to Burkholderia cepacia complex phage KL1, which together make up a taxonomic sub-family. Phages DLP1 and DLP2 exhibited significant differences in host ranges and growth kinetics.

CONCLUSIONS

The isolation and characterization of phages able to infect two completely different species of bacteria is an exciting discovery, as phages typically can only infect related bacterial species, and rarely infect bacteria across taxonomic families, let alone across taxonomic orders.

Bacteriophage-based therapy in cystic fibrosis-associated Pseudomonas aeruginosa infections: rationale and current status

Pulmonary infections involving Pseudomonas aeruginosa are among the leading causes of the deterioration of the respiratory status of cystic fibrosis (CF) patients. The emergence of multidrug-resistant strains in such populations, favored by iterative antibiotic cures, has led to the urgent need for new therapies. Among them, bacteriophage-based therapies deserve a focus. One century of empiric use in the ex-USSR countries suggests that bacteriophages may have beneficial effects against a large range of bacterial infections. Interest in bacteriophages has recently renewed in Western countries, and the in vitro data available suggest that bacteriophage-based therapy may be of significant interest for the treatment of pulmonary infections in CF patients. Although the clinical data concerning this specific population are relatively scarce, the beginning of the first large randomized study evaluating bacteriophage-based therapy in burn infections suggests that the time has come to assess the effectiveness of this new therapy in CF P. aeruginosa pneumonia. Consequently, the aim of this review is, after a brief history, to summarize the evidence concerning bacteriophage efficacy against P. aeruginosa and, more specifically, the in vitro studies, animal models, and clinical trials targeting CF.

Phage therapy of pulmonary infections

It is generally agreed that a bacteriophage-associated phenomenon was first unambiguously observed one-hundred years ago with the findings of Twort in 1915. This was independently followed by complementary observations by d'Hérelle in 1917. D'Hérelle's appreciation of the bacteriophage phenomenon appears to have directly led to the development of phages as antibacterial agents within a variety of contexts, including medical and agricultural. Phage use to combat nuisance bacteria appears to be especially useful where targets are sufficiently problematic, suitably bactericidal phages exist, and alternative approaches are lacking in effectiveness, availability, safety, or cost effectiveness, etc. Phage development as antibacterial agents has been strongest particularly when antibiotics have been less available or useful, e.g., such as in the treatment of chronic infections by antibiotic-resistant bacteria. One relatively under-explored or at least not highly reported use of phages as therapeutic agents has been to combat bacterial infections of the lungs and associated tissues. These infections are diverse in terms of their etiologies, manifestations, and also in terms of potential strategies of phage delivery. Here I review the literature considering the phage therapy of pulmonary and pulmonary-related infections, with emphasis on reports of clinical treatment along with experimental treatment of pulmonary infections using animal models.

Bacteriophage Delivery by Nebulization and Efficacy Against Phenotypically Diverse Pseudomonas aeruginosa from Cystic Fibrosis Patients

BACKGROUND

The rise in antibiotic-resistant Pseudomonas aeruginosa and the considerable difficulty in eradicating it from patients has re-motivated the study of bacteriophages as a therapeutic option. For this to be effective, host range and viability following nebulization need to be assessed. Host-range has not previously been assessed for the Liverpool Epidemic Strain (LES) isolates that are the most common cystic fibrosis-related clone of P. aeruginosa in the UK. Nebulization studies have not previously been linked to clinically relevant phages.

METHODS

84 phenotypically variable isolates of the LES were tested for susceptibility to seven bacteriophages known to have activity against P. aeruginosa. Five of the phages were from the Eliava Institute (IBMV) and 2 were isolated in this study. The viability of the two bacteriophages with the largest host ranges was characterized further to determine their ability to be nebulized and delivered to the lower airways. Phages were nebulized into a cascade impactor and the phage concentration was measured.

RESULTS

The bacteriophages tested killed between 66%-98% of the 84 Liverpool Epidemic Strain isolates. Two isolates were multi phage resistant, but were sensitive to most first line anti-Pseudomonal antibiotics. The amount of viable bacteriophages contained in particles that are likely to reach the lower airways (<4.7 μm) was 1% for the Omron and 12% AeroEclipse nebulizer.

CONCLUSIONS

Individual P. aeruginosa bacteriophages can lyse up to 98% of 84 phenotypically diverse LES strains. High titers of phages can be effectively nebulized.

Burkholderia cepacia complex Phage-Antibiotic Synergy (PAS): antibiotics stimulate lytic phage activity

The Burkholderia cepacia complex (Bcc) is a group of at least 18 species of Gram-negative opportunistic pathogens that can cause chronic lung infection in cystic fibrosis (CF) patients. Bcc organisms possess high levels of innate antimicrobial resistance, and alternative therapeutic strategies are urgently needed. One proposed alternative treatment is phage therapy, the therapeutic application of bacterial viruses (or bacteriophages). Recently, some phages have been observed to form larger plaques in the presence of sublethal concentrations of certain antibiotics; this effect has been termed phage-antibiotic synergy (PAS). Those reports suggest that some antibiotics stimulate increased production of phages under certain conditions. The aim of this study is to examine PAS in phages that infect Burkholderia cenocepacia strains C6433 and K56-2. Bcc phages KS12 and KS14 were tested for PAS, using 6 antibiotics representing 4 different drug classes. Of the antibiotics tested, the most pronounced effects were observed for meropenem, ciprofloxacin, and tetracycline. When grown with subinhibitory concentrations of these three antibiotics, cells developed a chain-like arrangement, an elongated morphology, and a clustered arrangement, respectively. When treated with progressively higher antibiotic concentrations, both the sizes of plaques and phage titers increased, up to a maximum. B. cenocepacia K56-2-infected Galleria mellonella larvae treated with phage KS12 and low-dose meropenem demonstrated increased survival over controls treated with KS12 or antibiotic alone. These results suggest that antibiotics can be combined with phages to stimulate increased phage production and/or activity and thus improve the efficacy of bacterial killing.