Phage therapy of pulmonary infections

Isolation and Biological Characteristics of a Novel Phage and Its Application to Control Vibrio Parahaemolyticus in Shellfish Meat

Vibrio parahaemolyticus is a common foodborne pathogenic bacterium. With the overuse of antibiotics, an increasing proportion of drug-resistant strains are emerging, which puts enormous pressure on public health. In this study, a V. parahaemolyticus-specific phage, VP41s3, was isolated. The head length, width, and tail length of the phage were 77.7 nm, 72.2 nm, and 17.5 nm, respectively. It remained active in the temperature range of 30-50°C and pH range of 4-11. The lytic curve of phage VP41s3 showed that the host bacteria did not grow until 11 h under phage treatment at MOI of 1000, indicating that the phage had good bacteriostatic ability. When it was added to shellfish contaminated with V. parahaemolyticus (15°C, 48 h), the number of bacteria in the experimental group was 2.11 log10 CFU/mL lower than that in the control group at 24 h. Furthermore, genomic characterization and phylogenetic analysis indicated that phage VP41s3 was a new member of the Podoviridae family. The genome contained 50 open reading frames (ORFs), in which the ORF19 (thymidine kinase) was an enzyme involved in the pyrimidine salvage pathway, which might lead to the accelerated DNA synthesis efficiency after phage entered into host cells. This study not only contributed to the improvement of phage database and the development of beneficial phage resources but also revealed the potential application of phage VP41s3 in food hygiene and safety.

Does Phage Therapy Need a Pan-Phage?

The emergence of multidrug-resistant bacteria is undoubtedly one of the most serious global health threats. One response to this threat that has been gaining momentum over the past decade is 'phage therapy'. According to this, lytic bacteriophages are used for the treatment of bacterial infections, either alone or in combination with antimicrobial agents. However, to ensure the efficacy and broad applicability of phage therapy, several challenges must be overcome. These challenges encompass the development of methods and strategies for the host range manipulation and bypass of the resistance mechanisms developed by pathogenic bacteria, as has been the case since the advent of antibiotics. As our knowledge and understanding of the interactions between phages and their hosts evolves, the key issue is to define the host range for each application. In this article, we discuss the factors that affect host range and how this determines the classification of phages into different categories of action. For each host range group, recent representative examples are provided, together with suggestions on how the different groups can be used to combat certain types of bacterial infections. The available methodologies for host range expansion, either through sequential adaptation to a new pathogen or through genetic engineering techniques, are also reviewed.

Bacteriophages as Potential Clinical Immune Modulators

Bacteriophages (phages for short) are bacteria-specific viruses that have been drawing attention when it comes to countering the ever-growing antibiotic bacterial resistance, and are being seen as one of the most promising technologies against multi-antibiotic-resistant bacteria. Although bacteriophages are commonly regarded only as anti-bacterial objects unable to directly interact with eukaryotic cell metabolism, an increasing quantity of evidence has indicated that bacteriophages can directly affect cells bacteria in both in vitro and in vivo applications, influencing the behavior of tissues and immune systems. In sight of this new range of applications, several authors have expressed enthusiasm in phage therapy as direct modulators of eukaryotic cells for clinical usage, highlighting the need for further investigations covering the pharmacology of these new "eukaryotic-viruses", as even harmful interactions with eukaryotic cells were detected after phage therapy. The present review aims to cover and highlight mechanisms through which bacteriophages may interact with immune cells, analyzing potential clinical applications and obstacles presented in the use of bacteriophages as anti-inflammatory tools.

The Potential of Bacteriophage-Antibiotic Combination Therapy in Treating Infections with Multidrug-Resistant Bacteria

The growing threat of antibiotic resistance is a significant global health challenge that has intensified in recent years. The burden of antibiotic resistance on public health is augmented due to its multifaceted nature, as well as the slow-paced and limited development of new antibiotics. The threat posed by resistance is now existential in phage therapy, which had long been touted as a promising replacement for antibiotics. Consequently, it is imperative to explore the potential of combination therapies involving antibiotics and phages as a feasible alternative for treating infections with multidrug-resistant bacteria. Although either bacteriophage or antibiotics can potentially treat bacterial infections, they are each fraught with resistance. Combination therapies, however, yielded positive outcomes in most cases; nonetheless, a few combinations did not show any benefit. Combination therapies comprising the synergistic activity of phages and antibiotics and combinations of phages with other treatments such as probiotics hold promise in the treatment of drug-resistant bacterial infections.

Personalized aerosolised bacteriophage treatment of a chronic lung infection due to multidrug-resistant Pseudomonas aeruginosa

Bacteriophage therapy has been suggested as an alternative or complementary strategy for the treatment of multidrug resistant (MDR) bacterial infections. Here, we report the favourable clinical evolution of a 41-year-old male patient with a Kartagener syndrome complicated by a life-threatening chronic MDR Pseudomonas aeruginosa infection, who is treated successfully with iterative aerosolized phage treatments specifically directed against the patient's isolate. We follow the longitudinal evolution of both phage and bacterial loads during and after phage administration in respiratory samples. Phage titres in consecutive sputum samples indicate in patient phage replication. Phenotypic analysis and whole genome sequencing of sequential bacterial isolates reveals a clonal, but phenotypically diverse population of hypermutator strains. The MDR phenotype in the collected isolates is multifactorial and mainly due to spontaneous chromosomal mutations. All isolates recovered after phage treatment remain phage susceptible. These results demonstrate that clinically significant improvement is achievable by personalised phage therapy even in the absence of complete eradication of P. aeruginosa lung colonization.

Phages for the treatment of Mycobacterium species

Highly drug-resistant strains are not uncommon among the Mycobacterium genus, with patients requiring lengthy antibiotic treatment regimens with multiple drugs and harmful side effects. This alarming increase in antibiotic resistance globally has renewed the interest in mycobacteriophage therapy for both Mycobacterium tuberculosis complex and non-tuberculosis mycobacteria. With the increasing number of genetically well-characterized mycobacteriophages and robust engineering tools to convert temperate phages to obligate lytic phages, the phage cache against extensive drug-resistant mycobacteria is constantly expanding. Synergistic effects between phages and TB drugs are also a promising avenue to research, with mycobacteriophages having several additional advantages compared to traditional antibiotics due to their different modes of action. These advantages include less side effects, a narrow host spectrum, biofilm penetration, self-replication at the site of infection and the potential to be manufactured on a large scale. In addition, mycobacteriophage enzymes, not yet in clinical use, warrant further studies with their additional benefits for rupturing host bacteria thereby limiting resistance development as well as showing promise in vitro to act synergistically with TB drugs. Before mycobacteriophage therapy can be envisioned as part of routine care, several obstacles must be overcome to translate in vitro work into clinical practice. Strategies to target intracellular bacteria and selecting phage cocktails to limit cross-resistance remain important avenues to explore. However, insight into pathophysiological host-phage interactions on a molecular level and innovative solutions to transcend mycobacteriophage therapy impediments, offer sufficient encouragement to explore phage therapy. Recently, the first successful clinical studies were performed using a mycobacteriophage-constructed cocktail to treat non-tuberculosis mycobacteria, providing substantial insight into lessons learned and potential pitfalls to avoid in order to ensure favorable outcomes. However, due to mycobacterium strain variation, mycobacteriophage therapy remains personalized, only being utilized in compassionate care cases until there is further regulatory approval. Therefore, identifying the determinants that influence clinical outcomes that can expand the repertoire of mycobacteriophages for therapeutic benefit, remains key for their future application.

Phages for treatment of Staphylococcus aureus infection

Combating multi-drug resistant bacterial infections should be a universal urgency. The gram- positive Staphylococcus aureus (S. aureus) bacteria are generally harmless; healthy people frequently have them on their skin and nose. These bacteria, for the most part, produce no difficulties or only minor skin diseases. Antibiotics and cleansing of the affected region are usually the treatments of choice. S. aureus can become virulent causing serious infections that may lead to pustules to sepsis or death. Normally, it is thought that antibiotics may solve problems concerning bacterial infection; but unfortunately, Staphylococci have evolved mechanisms to resist drugs. Methicillin-Resistant Staphylococcus aureus (MRSA); both in hospitals and in the community, infections are evolving into dangerous pathogens. Health care practitioners may need to use antibiotics with more adverse effects to treat antibiotic-resistant S. aureus infections. Amid existing efforts to resolve this problem, phage therapy proposes a hopeful alternate to face Staphylococcal infections. When the majority of antibiotics have failed to treat infections caused by multidrug-resistant bacteria, such as methicillin- and vancomycin-resistant S. aureus, phage therapy may be an option. Here, we appraise the potential efficacy, current knowledge on bacteriophages for S. aureus, experimental research and information on their clinical application, and limitations of phage therapy for S. aureus infections.

An evolving perspective on novel modified release drug delivery systems for inhalational therapy

INTRODUCTION

Drugs delivered via the lungs are predominantly used to treat various respiratory disorders, including asthma, chronic obstructive pulmonary diseases, respiratory tract infections and lung cancers, and pulmonary vascular diseases such as pulmonary hypertension. To treat respiratory diseases, targeted, modified or controlled release inhalation formulations are desirable for improved patient compliance and superior therapeutic outcome.

AREAS COVERED

This review summarizes the important factors that have an impact on the inhalable modified release formulation approaches with a focus toward various formulation strategies, including dissolution rate-controlled systems, drug complexes, site-specific delivery, drug-polymer conjugates, and drug-polymer matrix systems, lipid matrix particles, nanosystems, and formulations that can bypass clearance via mucociliary system and alveolar macrophages.

EXPERT OPINION

Inhaled modified release formulations can potentially reduce dosing frequency by extending drug's residence time in the lungs. However, inhalable modified or controlled release drug delivery systems remain unexplored and underdeveloped from the commercialization perspective. This review paper addresses the current state-of-the-art of inhaled controlled release formulations, elaborates on the avenues for developing newer technologies for formulating various drugs with tailored release profiles after inhalational delivery and explains the challenges associated with translational feasibility of modified release inhalable formulations.

Pharmacokinetics/pharmacodynamics of phage therapy: a major hurdle to clinical translation

BACKGROUND

The increasing emergence of antimicrobial resistance worldwide has led to renewed interest in phage therapy. Unlike antibiotics, the lack of pharmacokinetics/pharmacodynamics (PK/PD) information represents a major challenge for phage therapy. As therapeutic phages are biological entities with the ability to self-replicate in the presence of susceptible bacteria, their PK/PD is far more complicated than that of antibiotics.

OBJECTIVES

This narrative review examines the current literature on phage pharmacology and highlights major pharmacological challenges for phage therapy.

SOURCES

Included articles were identified by searching PubMed and Google Scholar till June 2022. The search terms were 'bacteriophage', 'antimicrobial', 'pharmacokinetics' and 'pharmacodynamics'. Additional relevant references were obtained from articles retrieved from the primary search.

CONTENT

In this review, phage PK is first discussed, focusing on absorption, distribution, metabolism, and elimination. Key factors affecting phage antimicrobial activities are reviewed, including multiplicity of infection, passive and active phage therapy, and the involvement of the human immune system. Importantly, we emphasize the impact of phage self-replication on the PK/PD and the fundamental phage characteristics that are required for PK/PD modelling and clinical translation.

IMPLICATIONS

Recent progress in phage pharmacology has shown that we are in a far better position now to treat infections with phage therapy than a century ago. However, phage therapy is still in its infancy when compared to antibiotics due to the scarce pharmacological knowledge (e.g. PK/PD). Optimization of phage PK/PD is key for translation of phage therapy in patients.

Phage therapy for pulmonary infections: lessons from clinical experiences and key considerations

Lower respiratory tract infections lead to significant morbidity and mortality. They are increasingly caused by multidrug-resistant pathogens, notably in individuals with cystic fibrosis, hospital-acquired pneumonia and lung transplantation. The use of bacteriophages (phages) to treat bacterial infections is gaining growing attention, with numerous published cases of compassionate treatment over the last few years. Although the use of phages appears safe, the lack of standardisation, the significant heterogeneity of published studies and the paucity of robust efficacy data, alongside regulatory hurdles arising from the existing pharmaceutical legislation, are just some of the challenges phage therapy has to overcome. In this review, we discuss the lessons learned from recent clinical experiences of phage therapy for the treatment of pulmonary infections. We review the key aspects, opportunities and challenges of phage therapy regarding formulations and administration routes, interactions with antibiotics and the immune system, and phage resistance. Building upon the current knowledge base, future pre-clinical studies using emerging technologies and carefully designed clinical trials are expected to enhance our understanding and explore the therapeutic potential of phage therapy.

Nanotechnological interventions of the microbiome as a next-generation antimicrobial therapy

The rise of antimicrobial resistance (AMR) impacts public health due to the diminished potency of existing antibiotics. The microbiome plays an important role in the host's immune system activity and shows the history of exposure to antimicrobials and its manipulation in combating antimicrobial resistance. Advancements in gene technologies, DNA sequencing, and computational biology have emerged as powerful platforms to better understand the relationship between animals and microorganisms (MOs). The past few years have witnessed an increase in the use of nanotechnology, both in industry and in academia, as tools to tackle antimicrobial resistance. New strategies of microbiome manipulation have been developed, such as the use of prebiotics, probiotics, peptides, antibodies, an appropriate diet, phage therapy, and the use of various nanotechnological techniques. Owing to the research outcomes, targeted delivery of antimicrobials with some modifications with nanoparticles can lead to the destruction of resistant microbial cells. In addition, nanoparticles have been studied for their potential antimicrobial effects both in vitro and in vivo. In this review, we highlight key opportunistic areas for applying nanotechnologies with the aim of manipulating the microbiome for the treatment of antimicrobial resistance. Besides providing a detailed review on various nanomaterials, technologies, opportunities, technical needs, and potential approaches for the manipulation of the microbiome to address these challenges, we discuss future challenges and our perspective.

Further Considerations on How to Improve Phage Therapy Experimentation, Practice, and Reporting: Pharmacodynamics Perspectives

Phage therapy uses bacterial viruses (bacteriophages) to infect and kill targeted pathogens. Approximately one decade ago, I started publishing on how possibly to improve upon phage therapy experimentation, practice, and reporting. Here, I gather and expand upon some of those suggestions. The issues emphasized are (1) that using ratios of antibacterial agents to bacteria is not how dosing is accomplished in the real world, (2) that it can be helpful to not ignore Poisson distributions as a means of either anticipating or characterizing phage therapy success, and (3) how to calculate a concept of 'inundative phage densities.' Together, these are issues of phage therapy pharmacodynamics, meaning they are ways of thinking about the potential for phage therapy treatments to be efficacious mostly independent of the details of delivery of phages to targeted bacteria. Much emphasis is placed on working with Poisson distributions to better align phage therapy with other antimicrobial treatments.

Clinical and experimental bacteriophage studies: Recommendations for possible approaches for standing against SARS-CoV-2

In 2019, the world faced a serious health challenge, the rapid spreading of a life-threatening viral pneumonia, coronavirus disease 2019 (COVID-19) caused by a betacoronavirus severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). As of January 2022 WHO statistics shows more than 5.6 million death and about 350 million infection by SARS-CoV-2. One of the life threatening aspects of COVID-19 is secondary infections and reduced efficacy of antibiotics against them. Since the beginning of COVID-19 many researches have been done on identification, treatment, and vaccine development. Bacterial viruses (bacteriophages) could offer novel approaches to detect, treat and control COVID-19. Phage therapy and in particular using phage cocktails can be used to control or eliminate the bacterial pathogen as an alternative or complementary therapeutic agent. At the same time, phage interaction with the host immune system can regulate the inflammatory response. In addition, phage display and engineered synthetic phages can be utilized to develop new vaccines and antibodies, stimulate the immune system, and elicit a rapid and well-appropriate defense response. The emergence of SARS-CoV-2 new variants like delta and omicron has proved the urgent need for precise, efficient and novel approaches for vaccine development and virus detection techniques in which bacteriophages may be one of the plausible solutions. Therefore, phages with similar morphology and/or genetic content to that of coronaviruses can be used for ecological and epidemiological modeling of SARS-CoV-2 behavior and future generations of coronavirus, and in general new viral pathogens. This article is a comprehensive review/perspective of potential applications of bacteriophages in the fight against the present pandemic and the post-COVID era.

Prospects of Inhaled Phage Therapy for Combatting Pulmonary Infections

With respiratory infections accounting for significant morbidity and mortality, the issue of antibiotic resistance has added to the gravity of the situation. Treatment of pulmonary infections (bacterial pneumonia, cystic fibrosis-associated bacterial infections, tuberculosis) is more challenging with the involvement of multi-drug resistant bacterial strains, which act as etiological agents. Furthermore, with the dearth of new antibiotics available and old antibiotics losing efficacy, it is prudent to switch to non-antibiotic approaches to fight this battle. Phage therapy represents one such approach that has proven effective against a range of bacterial pathogens including drug resistant strains. Inhaled phage therapy encompasses the use of stable phage preparations given via aerosol delivery. This therapy can be used as an adjunct treatment option in both prophylactic and therapeutic modes. In the present review, we first highlight the role and action of phages against pulmonary pathogens, followed by delineating the different methods of delivery of inhaled phage therapy with evidence of success. The review aims to focus on recent advances and developments in improving the final success and outcome of pulmonary phage therapy. It details the use of electrospray for targeted delivery, advances in nebulization techniques, individualized controlled inhalation with software control, and liposome-encapsulated nebulized phages to take pulmonary phage delivery to the next level. The review expands knowledge on the pulmonary delivery of phages and the advances that have been made for improved outcomes in the treatment of respiratory infections.

Mycobacteriophages to Treat Tuberculosis: Dream or Delusion?

Rates of antimicrobial resistance are increasing globally while the pipeline of new antibiotics is drying up, putting patients with disease caused by drug-resistant bacteria at increased risk of complications and death. The growing costs for diagnosis and management of drug resistance threaten tuberculosis control where the disease is endemic and resources limited. Bacteriophages are viruses that attack bacteria. Phage preparations served as anti-infective agents long before antibiotics were discovered. Though small in size, phages are the most abundant and diverse biological entity on earth. Phages have co-evolved with their hosts and possess all the tools needed to infect and kill bacteria, independent of drug resistance. Modern biotechnology has improved our understanding of the biology of phages and their possible uses. Phage preparations are available to treat meat, fruit, vegetables, and dairy products against parasites or to prevent contamination with human pathogens, such as Listeria monocytogenes, Escherichia coli, or Staphylococcus aureus. Such phage-treated products are considered fit for human consumption. A number of recent case reports describe in great detail the successful treatment of highly drug-resistant infections with individualized phage preparations. Formal clinical trials with standardized products are slowly emerging. With its highly conserved genome and relative paucity of natural phage defence mechanisms Mycobacterium tuberculosis appears to be a suitable target for phage treatment. A phage cocktail with diverse and strictly lytic phages that kill all lineages of M. tuberculosis, and can be propagated on Mycobacterium smegmatis, has been assembled and is available for the evaluation of optimal dosage and suitable routes of administration for tuberculosis in humans. Phage treatment can be expected to be safe and active on extracellular organisms, but phage penetration to intracellular and granulomatous environments as well as synergistic effects with antibiotics are important questions to address during further evaluation.

Phage Therapy in the 21st Century: Is There Modern, Clinical Evidence of Phage-Mediated Efficacy?

Many bacteriophages are obligate killers of bacteria. That this property could be medically useful was first recognized over one hundred years ago, with 2021 being the 100-year anniversary of the first clinical phage therapy publication. Here we consider modern use of phages in clinical settings. Our aim is to answer one question: do phages serve as effective anti-bacterial infection agents when used clinically? An important emphasis of our analyses is on whether phage therapy-associated anti-bacterial infection efficacy can be reasonably distinguished from that associated with often coadministered antibiotics. We find that about half of 70 human phage treatment reports-published in English thus far in the 2000s-are suggestive of phage-mediated anti-bacterial infection efficacy. Two of these are randomized, double-blinded, infection-treatment studies while 14 of those studies, in our opinion, provide superior evidence of a phage role in observed treatment successes. Roughly three-quarters of these potentially phage-mediated outcomes are based on microbiological as well as clinical results, with the rest based on clinical success. Since many of these phage treatments are of infections for which antibiotic therapy had not been successful, their collective effectiveness is suggestive of a valid utility in employing phages to treat otherwise difficult-to-cure bacterial infections.

Improving Phage-Biofilm In Vitro Experimentation

Bacteriophages or phages, the viruses of bacteria, are abundant components of most ecosystems, including those where bacteria predominantly occupy biofilm niches. Understanding the phage impact on bacterial biofilms therefore can be crucial toward understanding both phage and bacterial ecology. Here, we take a critical look at the study of bacteriophage interactions with bacterial biofilms as carried out in vitro, since these studies serve as bases of our ecological and therapeutic understanding of phage impacts on biofilms. We suggest that phage-biofilm in vitro experiments often may be improved in terms of both design and interpretation. Specific issues discussed include (a) not distinguishing control of new biofilm growth from removal of existing biofilm, (b) inadequate descriptions of phage titers, (c) artificially small overlying fluid volumes, (d) limited explorations of treatment dosing and duration, (e) only end-point rather than kinetic analyses, (f) importance of distinguishing phage enzymatic from phage bacteriolytic anti-biofilm activities, (g) limitations of biofilm biomass determinations, (h) free-phage interference with viable-count determinations, and (i) importance of experimental conditions. Toward bettering understanding of the ecology of bacteriophage-biofilm interactions, and of phage-mediated biofilm disruption, we discuss here these various issues as well as provide tips toward improving experiments and their reporting.

The clinical path to deliver encapsulated phages and lysins

The global emergence of multidrug-resistant pathogens is shaping the current dogma regarding the use of antibiotherapy. Many bacteria have evolved to become resistant to conventional antibiotherapy, representing a health and economic burden for those afflicted. The search for alternative and complementary therapeutic approaches has intensified and revived phage therapy. In recent decades, the exogenous use of lysins, encoded in phage genomes, has shown encouraging effectiveness. These two antimicrobial agents reduce bacterial populations; however, many barriers challenge their prompt delivery at the infection site. Encapsulation in delivery vehicles provides targeted therapy with a controlled compound delivery, surpassing chemical, physical and immunological barriers that can inactivate and eliminate them. This review explores phages and lysins' current use to resolve bacterial infections in the respiratory, digestive, and integumentary systems. We also highlight the different challenges they face in each of the three systems and discuss the advances towards a more expansive use of delivery vehicles.

A Phage Therapy Guide for Clinicians and Basic Scientists: Background and Highlighting Applications for Developing Countries

Approximately 10% of global health research is devoted to 90% of global disease burden (the so-called “10/90 Gap”) and it often neglects those diseases most prevalent in low-income countries. Antibiotic resistant bacterial infections are known to impact on healthcare, food security, and socio-economic fabric in the developing countries. With a global antibiotic resistance crisis currently reaching a critical level, the unmet needs in the developing countries are even more striking. The failure of traditional antimicrobials has led to renewed interest in century-old bacteriophage (phage) therapy in response to the urgent need to develop alternative therapies to treat infections. Phage therapy may have particular value in developing countries where relevant phages can be sourced and processed locally and efficiently, breaking specifically the economic barrier of access to expensive medicine. Hence this makes phage therapy an attractive and feasible option. In this review, we draw our respective clinical experience as well as phage therapy research and clinical trial, and discuss the ways in which phage therapy might reduce the burden of some of the most important bacterial infections in developing countries.

Potential for bacteriophage therapy for Staphylococcus aureus pneumonia with influenza A coinfection

The ability of influenza A virus to evolve, coupled with increasing antimicrobial resistance, could trigger an influenza pandemic with great morbidity and mortality. Much of the 1918 influenza pandemic mortality was likely due to bacterial coinfection, including Staphylococcus aureus pneumonia. S. aureus resists many antibiotics. The lack of new antibiotics suggests alternative antimicrobials, such as bacteriophages, are needed. Potential delivery routes for bacteriophage therapy (BT) include inhalation and intravenous injection. BT has recently been used successfully in compassionate access pulmonary infection cases. Phage lysins, enzymes that hydrolyze bacterial cell walls and which are bactericidal, are efficacious in animal pneumonia models. Clinical trials will be needed to determine whether BT can ameliorate disease in influenza and S. aureus coinfection.

Interactions of Bacteriophages and Bacteria at the Airway Mucosa: New Insights Into the Pathophysiology of Asthma

The airway epithelium is the primary site where inhaled and resident microbiota interacts between themselves and the host, potentially playing an important role on allergic asthma development and pathophysiology. With the advent of culture independent molecular techniques and high throughput technologies, the complex composition and diversity of bacterial communities of the airways has been well-documented and the notion of the lungs' sterility definitively rejected. Recent studies indicate that the microbial composition of the asthmatic airways across the spectrum of disease severity, differ significantly compared with healthy individuals. In parallel, a growing body of evidence suggests that bacterial viruses (bacteriophages or simply phages), regulating bacterial populations, are present in almost every niche of the human body and can also interact directly with the eukaryotic cells. The triptych of airway epithelial cells, bacterial symbionts and resident phages should be considered as a functional and interdependent unit with direct implications on the respiratory and overall homeostasis. While the role of epithelial cells in asthma pathophysiology is well-established, the tripartite interactions between epithelial cells, bacteria and phages should be scrutinized, both to better understand asthma as a system disorder and to explore potential interventions.

Mycobacteriophages as Potential Therapeutic Agents against Drug-Resistant Tuberculosis

The current emergence of multi-, extensively-, extremely-, and total-drug resistant strains of Mycobacterium tuberculosis poses a major health, social, and economic threat, and stresses the need to develop new therapeutic strategies. The notion of phage therapy against bacteria has been around for more than a century and, although its implementation was abandoned after the introduction of drugs, it is now making a comeback and gaining renewed interest in Western medicine as an alternative to treat drug-resistant pathogens. Mycobacteriophages are genetically diverse viruses that specifically infect mycobacterial hosts, including members of the M. tuberculosis complex. This review describes general features of mycobacteriophages and their mechanisms of killing M. tuberculosis, as well as their advantages and limitations as therapeutic and prophylactic agents against drug-resistant M. tuberculosis strains. This review also discusses the role of human lung micro-environments in shaping the availability of mycobacteriophage receptors on the M. tuberculosis cell envelope surface, the risk of potential development of bacterial resistance to mycobacteriophages, and the interactions with the mammalian host immune system. Finally, it summarizes the knowledge gaps and defines key questions to be addressed regarding the clinical application of phage therapy for the treatment of drug-resistant tuberculosis.

Postbiotic-Enabled Targeting of the Host-Microbiota-Pathogen Interface: Hints of Antibiotic Decline?

Mismanagement of bacterial infection therapies has undermined the reliability and efficacy of antibiotic treatments, producing a profound crisis of the antibiotic drug market. It is by now clear that tackling deadly infections demands novel strategies not only based on the mere toxicity of anti-infective compounds. Host-directed therapies have been the first example as novel treatments with alternate success. Nevertheless, recent advances in the human microbiome research have provided evidence that compounds produced by the microbial metabolism, namely postbiotics, can have significant impact on human health. Such compounds target the host-microbe-pathogen interface rescuing biotic and immune unbalances as well as inflammation, thus providing novel therapeutic opportunities. This work discusses critically, through literature review and personal contributions, these novel nonantibiotic treatment strategies for infectious disease management and resistance prevention, which could represent a paradigm change rocking the foundation of current antibiotic therapy tenets.

P. aeruginosa flow-cell biofilms are enhanced by repeated phage treatments but can be eradicated by phage-ciprofloxacin combination

Phage therapy has shown promising results in the treatment of Pseudomonas aeruginosa biofilm infections in animal studies and case reports. The aim of this study was to quantify effects of phage treatments on P. aeruginosa biofilm production and structure. Confocal scanning microscopy was used to follow the interaction between a cocktail of three virulent phages and P. aeruginosa flow-cell biofilms. The role of (i) biofilm age, (ii) repeated phage treatments, (iii) alginate production and (iv) the combination with sub-MIC levels of ciprofloxacin was investigated. Single phage treatment in the early biofilm stages significantly reduced P. aeruginosa PAO1 biovolume (85%-98% reduction). Repeated phage treatments increased the biovolume from 18.25 (untreated biofilm) to 22.24 and 31.07 µm3/µm2 for biofilms treated with phages twice and thrice, respectively. Alginate protected against the phage treatment as the live biovolume remained unaffected by the phage treatment in the mucoid biofilm (20.11 µm3/µm2 in untreated and 21.74 µm3/µm2 in phage-treated biofilm) but decreased in the PAO1 biofilm from 27.35 to 0.89 µm3/µm2. We show that the combination of phages with antibiotics at sub-MIC levels caused a ∼6 log units reduction in the abundance of P. aeruginosa cells in biofilms and that phage treatment increased the size of microcolonies in flow-cell system.

Pharmacologically Aware Phage Therapy: Pharmacodynamic and Pharmacokinetic Obstacles to Phage Antibacterial Action in Animal and Human Bodies

The use of viruses infecting bacteria (bacteriophages or phages) to treat bacterial infections has been ongoing clinically for approximately 100 years. Despite that long history, the growing international crisis of resistance to standard antibiotics, abundant anecdotal evidence of efficacy, and one successful modern clinical trial of efficacy, this phage therapy is not yet a mainstream approach in medicine. One explanation for why phage therapy has not been subject to more widespread implementation is that phage therapy research, both preclinical and clinical, can be insufficiently pharmacologically aware. Consequently, here we consider the pharmacological obstacles to phage therapy effectiveness, with phages in phage therapy explicitly being considered to serve as drug equivalents. The study of pharmacology has traditionally been differentiated into pharmacokinetic and pharmacodynamic aspects. We therefore separately consider the difficulties that phages as virions can have in traveling through body compartments toward reaching their target bacteria (pharmacokinetics) and the difficulties that phages can have in exerting antibacterial activity once they have reached those bacteria (pharmacodynamics). The latter difficulties, at least in part, are functions of phage host range and bacterial resistance to phages. Given the apparently low toxicity of phages and the minimal side effects of phage therapy as practiced, phage therapy should be successful so long as phages can reach the targeted bacteria in sufficiently high numbers, adsorb, and then kill those bacteria. Greater awareness of what obstacles to this success generally or specifically can exist, as documented in this review, should aid in the further development of phage therapy toward wider use.

Phage-Antibiotic Combination Treatments: Antagonistic Impacts of Antibiotics on the Pharmacodynamics of Phage Therapy?

Bacteria can evolve resistance to antibiotics. Even without changing genetically, bacteria also can display tolerance to antibiotic treatments. Many antibiotics are also broadly acting, as can result in excessive modifications of body microbiomes. Particularly for antibiotics of last resort or in treating extremely ill patients, antibiotics furthermore can display excessive toxicities. Antibiotics nevertheless remain the standard of care for bacterial infections, and rightly so given their long track records of both antibacterial efficacy and infrequency of severe side effects. Antibiotics do not successfully cure all treated bacterial infections, however, thereby providing a utility to alternative antibacterial approaches. One such approach is the use of bacteriophages, the viruses of bacteria. This nearly 100-year-old bactericidal, anti-infection technology can be effective against antibiotic-resistant or -tolerant bacteria, including bacterial biofilms and persister cells. Ideally phages could be used in combination with standard antibiotics while retaining their anti-bacterial pharmacodynamic activity, this despite antibiotics interfering with aspects of bacterial metabolism that are also required for full phage infection activity. Here I examine the literature of pre-clinical phage-antibiotic combination treatments, with emphasis on antibiotic-susceptible bacterial targets. I review evidence of antibiotic interference with phage infection activity along with its converse: phage antibacterial functioning despite antibiotic presence.

Prophylaxis of Mycobacterium tuberculosis H37Rv Infection in a Preclinical Mouse Model via Inhalation of Nebulized Bacteriophage D29

Globally, more people die annually from tuberculosis than from any other single infectious agent. Unfortunately, there is no commercially-available vaccine that is sufficiently effective at preventing acquisition of pulmonary tuberculosis in adults. In this study, pre-exposure prophylactic pulmonary delivery of active aerosolized anti-tuberculosis bacteriophage D29 was evaluated as an option for protection against Mycobacterium tuberculosis infection. An average bacteriophage concentration of approximately 1 PFU/alveolus was achieved in the lungs of mice using a nose-only inhalation device optimized with a dose simulation technique and adapted for use with a vibrating mesh nebulizer. Within 30 minutes of bacteriophage delivery, the mice received either a low dose (∼50-100 CFU), or an ultra-low dose (∼5-10 CFU), of M. tuberculosis H37Rv aerosol to the lungs. A prophylactic effect was observed with bacteriophage aerosol pre-treatment significantly decreasing M. tuberculosis burden in mouse lungs 24 hours and 3 weeks post-challenge (p < 0.05). These novel results indicate that a sufficient dose of nebulized mycobacteriophage aerosol to the lungs may be a valuable intervention to provide extra protection to health care professionals and other individuals at risk of exposure to M. tuberculosis.

Factors determining phage stability/activity: challenges in practical phage application

Introduction: Phages consist of nucleic acids and proteins that may lose their activity under different physico-chemical conditions. The production process of phage formulations may decrease phage infectivity. Ingredients present in the preparation may influence phage particles, although preparation and storage conditions may also cause variations in phage titer. Significant factors are the manner of phage application, the patient's immune system status, the type of medication being taken, and diet. Areas covered: We discuss factors determining phage activity and stability, which is relevant for the preparation and application of phage formulations with the highest therapeutic efficacy. Our article should be helpful for more insightful implementation of clinical trials, which could pave the way for successful phage therapy. Expert opinion: The number of naturally occurring phages is practically unlimited and phages vary in their susceptibility to external factors. Modern methods offer engineering techniques which should lead to enhanced precision in phage delivery and anti-bacterial activity. Recent data suggesting that phages may also be used in treating nonbacterial infections as well as anti-inflammatory and immunomodulatory agents add further weight to such studies. It may be anticipated that different phage activities could have varying susceptibility to factors determining their actions.

Bacteriophage interactions with mammalian tissue: Therapeutic applications

The human body is a large reservoir for bacterial viruses known as bacteriophages (phages), which participate in dynamic interactions with their bacterial and human hosts that ultimately affect human health. The current growing interest in human resident phages is paralleled by new uses of phages, including the design of engineered phages for therapeutic applications. Despite the increasing number of clinical trials being conducted, the understanding of the interaction of phages and mammalian cells and tissues is still largely unknown. The presence of phages in compartments within the body previously considered purely sterile, suggests that phages possess a unique capability of bypassing anatomical and physiological barriers characterized by varying degrees of selectivity and permeability. This review will discuss the direct evidence of the accumulation of bacteriophages in various tissues, focusing on the unique capability of phages to traverse relatively impermeable barriers in mammals and its relevance to its current applications in therapy.

Use of phage therapy to treat long-standing, persistent, or chronic bacterial infections

Viruses of bacteria - known as bacteriophages or phages - have been used clinically as antibacterial agents for nearly 100 years. Often this phage therapy is of long-standing, persistent, or chronic bacterial infections, and this can be particularly so given prior but insufficiently effective infection treatment using standard antibiotics. Such infections, in turn, often have a biofilm component. Phages in modern medicine thus are envisaged to serve especially as anti-biofilm/anti-persistent infection agents. Here I review the English-language literature concerning in vivo experimental and clinical phage treatment of longer-lived bacterial infections. Overall, published data appears to be supportive of a relatively high potential for phages to cure infections which are long standing and which otherwise have resisted treatment with antibieiotics.

Phage therapy: What factors shape phage pharmacokinetics and bioavailability? Systematic and critical review

Bacteriophages are not forgotten viruses anymore: scientists and practitioners seek to understand phage pharmacokinetics in animals and humans, investigating bacteriophages as therapeutics, nanocarriers or microbiome components. This review provides a comprehensive overview of factors that determine phage circulation, penetration, and clearance, and that in consequence determine phage applicability for medicine. It makes use of experimental data collected by the phage community so far (PubMed 1924‐2016, including non‐English reports), combining elements of critical and systematic review.

This study covers phage ability to enter a system by various routes of administration, how (and if) the phage may access various tissues and organs, and finally what mechanisms determine the courses of phage clearance. The systematic review method was applied to analyze (i) phage survival in the gut (gut transit) and (ii) phage ability to enter the mammalian system by many administration routes. Aspects that have not yet been covered by a sufficient number of reports for mathematical analysis, as well as mechanisms underlying trends, are discussed in the form of a critical review.

In spite of the extraordinary diversity of bacteriophages and possible phage applications, the analysis revealed that phage morphology, phage specificity, phage dose, presence of sensitive bacteria or the characteristics of treated individuals (age, taxonomy) may affect phage bioavailability in animals and humans. However, once phages successfully enter the body, they reach most organs, including the central nervous system. Bacteriophages are cleared mainly by the immune system: innate immunity removes phages even when no specific response to bacteriophages has yet developed.

Alternatives to Conventional Antibiotics in the Era of Antimicrobial Resistance

As more antibiotics are rendered ineffective by drug-resistant bacteria, focus must be shifted towards alternative therapies for treating infections. Although several alternatives already exist in nature, the challenge is to implement them in clinical use. Advancements within biotechnology, genetic engineering, and synthetic chemistry have opened up new avenues towards the search for therapies that can substitute for antibiotics. This review provides an introduction to the various promising approaches that have been adopted in this regard. Whilst the use of bacteriophages and antibodies has been partly implemented, other promising strategies, such as probiotics, lysins, and antimicrobial peptides, are in various stages of development. Propitious concepts such as genetically modified phages, antibacterial oligonucleotides, and CRISPR-Cas9 are also discussed.

Clinical Indications and Compassionate Use of Phage Therapy: Personal Experience and Literature Review with a Focus on Osteoarticular Infections

The history of phage therapy started with its first clinical application in 1919 and continues its development to this day. Phages continue to lack any market approval in Western medicine as a recognized drug, but are increasingly used as an experimental therapy for the compassionate treatment of patients experiencing antibiotic failure. The few formal experimental phage clinical trials that have been completed to date have produced inconclusive results on the efficacy of phage therapy, which contradicts the many successful treatment outcomes observed in historical accounts and recent individual case reports. It would therefore be wise to identify why such a discordance exists between trials and compassionate use in order to better develop future phage treatment and clinical applications. The multitude of observations reported over the years in the literature constitutes an invaluable experience, and we add to this by presenting a number of cases of patients treated compassionately with phages throughout the past decade with a focus on osteoarticular infections. Additionally, an abundance of scientific literature into phage-related areas is transforming our knowledge base, creating a greater understanding that should be applied for future clinical applications. Due to the increasing number of treatment failures anticipatedfrom the perspective of a possible post-antibiotic era, we believe that the introduction of bacteriophages into the therapeutic arsenal seems a scientifically sound and eminently practicable consideration today as a substitute or adjuvant to antibiotic therapy.

Use of a Primary Epithelial Cell Screening Tool to Investigate Phage Therapy in Cystic Fibrosis

Antimicrobial-resistant microbes are an increasing threat to human health. In cystic fibrosis (CF), airway infections with Pseudomonas aeruginosa remain a key driver of lung damage. With few new antibiotics on the development horizon, alternative therapeutic approaches are needed against antimicrobial-resistant pathogens. Phage therapy, or the use of viruses that infect bacteria, is one proposed novel therapy to treat bacterial infections. However, the airways are complex microenvironments with unique characteristics that may affect the success of novel therapies. Here, three phages of P. aeruginosa (E79, F116, and one novel clinically derived isolate, designated P5) were screened for activity against 21 P. aeruginosa strains isolated from children with CF. Of these, phage E79 showed broad antibacterial activity (91% of tested strains sensitive) and was selected for further assessment. E79 genomic DNA was extracted, sequenced, and confirmed to contain no bacterial pathogenicity genes. High titre phage preparations were then purified using ion-exchange column chromatography and depleted of bacterial endotoxin. Primary airway epithelial cells derived from children with CF (n = 8, age range 0.2–5.5 years, 5 males) or healthy non-CF controls (n = 8, age range 2.5–4.0 years, 4 males) were then exposed to purified phage for 48 h. Levels of inflammatory IL-1β, IL-6, and IL-8 cytokine production were measured in culture supernatant by immunoassays and the extent of cellular apoptosis was measured using a ssDNA kit. Cytokine and apoptosis levels were compared between E79-stimulated and unstimulated controls, and, encouragingly, purified preparations of E79 did not stimulate any significant inflammatory cytokine responses or induce apoptosis in primary epithelial cells derived from children with or without CF. Collectively, this study demonstrates the feasibility of utilizing pre-clinical in vitro culture models to screen therapeutic candidates, and the potential of E79 as a therapeutic phage candidate in CF.

Lower Airway Virology in Health and Disease-From Invaders to Symbionts

Studies of human airway virome are relatively recent and still very limited. Culture-independent microbial techniques showed growing evidence of numerous viral communities in the respiratory microbial ecosystem. The significance of different acute respiratory viruses is already known in the pathogenesis of chronic conditions, such as asthma, cystic fibrosis (CF), or chronic obstructive lung disease (COPD), and their exacerbations. Viral pathogens, such as influenza, metapneumovirus, parainfluenza, respiratory syncytial virus, or rhinovirus, have been associated with impaired immune response, acute exacerbations, and decrease in lung function in chronic lung diseases. However, more data have attributed a role to Herpes family viruses or the newly identified Anelloviridae family of viruses in chronic diseases, such as asthma, idiopathic pulmonary fibrosis (IPF), or CF. Impaired antiviral immunity, bacterial colonization, or used medication, such as glucocorticoids or antibiotics, contribute to the imbalance of airway microbiome and may shape the local viral ecosystem. A specific part of virome, bacteriophages, frames lung microbial communities through direct contact with its host, the specific bacteria known as Pseudomonas aeruginosa or their biofilm formation. Moreover, antibiotic resistance is induced through phages via horizontal transfer and leads to more severe exacerbations of chronic airway conditions. Morbidity and mortality of asthma, COPD, CF, and IPF remains high, despite an increased understanding and knowledge about the impact of respiratory virome in the pathogenesis of these conditions. Thus, more studies focus on new prophylactic methods or therapeutic agents directed toward viral⁻host interaction, microbial metabolic function, or lung microbial composition rearrangement.

Synergy of nebulized phage PEV20 and ciprofloxacin combination against Pseudomonas aeruginosa

Nebulization is currently used for delivery of antibiotics for respiratory infections. Bacteriophages (or phages) are effective predators of pathogens including Pseudomonas aeruginosa commonly found in the lungs of patients with cystic fibrosis (CF). It is known that phages and antibiotics can potentially show synergistic antimicrobial effect on bacterial killing. In the present study, we investigated synergistic antimicrobial effect of phage PEV20 with five different antibiotics against three P. aeruginosa strains isolated from sputum of CF patients. The antibiotics included ciprofloxacin, tobramycin, colistin, aztreonam and amikacin, which are approved by U.S Food and Drug Administration (FDA) for inhaled administration. Phage and antibiotic synergy was determined by assessing bacterial killing performing time-kill studies. Among the different phage-antibiotic combinations, PEV20 and ciprofloxacin exhibited the most synergistic effect. Two phage-ciprofloxacin combinations, containing 1/4 and 1/2 of the minimum inhibitory concentration (MIC) of ciprofloxacin against P. aeruginosa strains FADD1-PA001 (A) and JIP865, respectively were aerosolized using both air-jet and vibrating mesh nebulizers and the synergistic antibacterial activity was maintained after nebulization. Air-jet nebulizer generated droplets with smaller volume median diameters (3.6-3.7 µm) and slightly larger span (2.3-2.4) than vibrating mesh nebulizers (5.1-5.3 µm; 2.1-2.2), achieving a higher fine particle fraction (FPF) of 70%. In conclusion, nebulized phage PEV20 and ciprofloxacin combination shows promising antimicrobial and aerosol characteristics for potential treatment of respiratory tract infections caused by drug-resistant P. aeruginosa.

Refractory Pseudomonas Bacteremia in a 2-Year-Old Sterilized by Bacteriophage Therapy

Here, we report a complex case that involved a pediatric patient who experienced recalcitrant multidrug-resistant Pseudomonas aeruginosa infection complicated by bacteremia/sepsis; our antibacterial options were limited because of resistance, allergies, and suboptimal source control. A cocktail of 2 bacteriophages targeting the infectious organism introduced on 2 separate occasions sterilized the bacteremia.

Phage therapy for respiratory infections

A respiratory infection caused by antibiotic-resistant bacteria can be life-threatening. In recent years, there has been tremendous effort put towards therapeutic application of bacteriophages (phages) as an alternative or supplementary treatment option over conventional antibiotics. Phages are natural parasitic viruses of bacteria that can kill the bacterial host, including antibiotic-resistant bacteria. Inhaled phage therapy involves the development of stable phage formulations suitable for inhalation delivery followed by preclinical and clinical studies for assessment of efficacy, pharmacokinetics and safety. We presented an overview of recent advances in phage formulation for inhalation delivery and their efficacy in acute and chronic rodent respiratory infection models. We have reviewed and presented on the prospects of inhaled phage therapy as a complementary treatment option with current antibiotics and as a preventative means. Inhaled phage therapy has the potential to transform the prevention and treatment of bacterial respiratory infections, including those caused by antibiotic-resistant bacteria.

Production of Bacteriophages by Listeria Cells Entrapped in Organic Polymers

Applications for bacteriophages as antimicrobial agents are increasing. The industrial use of these bacterial viruses requires the production of large amounts of suitable strictly lytic phages, particularly for food and agricultural applications. This work describes a new approach for phage production. Phages H387 (Siphoviridae) and A511 (Myoviridae) were propagated separately using Listeria ivanovii host cells immobilised in alginate beads. The same batch of alginate beads could be used for four successive and efficient phage productions. This technique enables the production of large volumes of high-titer phage lysates in continuous or semi-continuous (fed-batch) cultures.

Chemotherapy with Phage Lysins Reduces Pneumococcal Colonization of the Respiratory Tract

Bacteriophage-borne lytic enzymes, also named lysins or enzybiotics, are efficient agents for the killing of bacterial pathogens. The colonization of the respiratory tract by Streptococcus pneumoniae is a prerequisite for the establishment of the infection process. Hence, we have evaluated the antibacterial activities of three different lysins against pneumococcal colonization using human nasopharyngeal and lung epithelial cells as well as a mouse model of nasopharyngeal colonization. The lysins tested were the wild-type Cpl-1, the engineered Cpl-7S, and the chimera Cpl-711. Moreover, we included amoxicillin as a comparator antibiotic. Human epithelial cells were infected with three different multidrug-resistant clinical isolates of S. pneumoniae followed by a single dose of the corresponding lysin. The antimicrobial activities of these lysins were also evaluated using a mouse nasopharyngeal carriage model. The exposure of the infected epithelial cells to Cpl-7S did not result in the killing of any of the pneumococcal strains investigated. However, the treatment with Cpl-1 or Cpl-711 increased the killing of S. pneumoniae organisms adhered to both types of human epithelial cells, with Cpl-711 being more effective than Cpl-1, at subinhibitory concentrations. In addition, a treatment with amoxicillin had no effect on reducing the carrier state, whereas mice treated by the intranasal route with Cpl-711 showed significantly reduced nasopharyngeal colonization, with no detection of bacterial load in 20 to 40% of the mice. This study indicates that Cpl-1 and Cpl-711 lysins might be promising antimicrobial candidates for therapy against pneumococcal colonization.

Bacteriophage Clinical Use as Antibacterial "Drugs": Utility and Precedent

For phage therapy-the treatment of bacterial infections using bacterial viruses-a key issue is the conflict between apparent ease of clinical application, on the one hand, and on the other hand, numerous difficulties that can be associated with undertaking preclinical development. These conflicts between achieving efficacy in the real world versus rigorously understanding that efficacy should not be surprising because equivalent conflicts have been observed in applied biology for millennia: exploiting the inherent, holistic tendencies of useful systems, e.g., of dairy cows, inevitably is easier than modeling those systems or maintaining effectiveness while reducing such systems to isolated parts. Trial and error alone, in other words, can be a powerful means toward technological development. Undertaking trial and error-based programs, especially in the clinic, nonetheless is highly dependent on those technologies possessing both inherent safety and intrinsic tendencies toward effectiveness, but in this modern era we tend to forget that ideally there would exist antibacterials which could be thus developed, that is, with tendencies toward both safety and effectiveness, and which are even relatively inexpensive. Consequently, we tend to demand rigor as well as expense of development even to the point of potentially squandering such utility, were it to exist. In this review I lay out evidence that in phage therapy such potential, in fact, does exist. Advancement of phage therapy unquestionably requires effective regulation as well as rigorous demonstration of efficacy, but after nearly 100 years of clinical practice, perhaps not as much emphasis on strictly laboratory-based proof of principle.

Phage Therapy: Various Perspectives on How to Improve the Art

Use of phages as antibacterial agents has a long and, even, storied history. During that time much has been learned but, to a degree, also forgotten. As a consequence, today we experience a largely preclinical development of a field which already has been subject to substantial clinical practice. This development, as well, is now occurring within a much more rigorously regulated environment than previously had been the case. The consequence is not only a need to reinvent standards of practice but to do so within a more explicitly pharmacological context. Of particular concern is that the application of phages to bacterial infections does not always result in control of the latter, necessitating ongoing thought on how to refine treatment protocols. Here I consider a number of issues relevant to such refinement, focusing on areas which, in my opinion, phage therapy researchers-perhaps especially those new to the field-might struggle with. In order of presentation, I consider how best to describe phage therapy within publications toward achieving a more coherent literature, the importance of Poisson distributions along with killing titers toward understanding phage dosing, the associated importance of establishing sufficient phage numbers in situ to achieve adequate bacteria killing, various problems with the use of multiplicity of infection (MOI) as a description of phage dosing, how to anticipate the basic kinetics of phage-bacteria absorptive interactions, how to distinguish passive from active treatments, and basic approaches toward addressing disappointing efficacy outcomes.