THE MULTIPLICATION OF BACTERIOPHAGE IN VIVO AND ITS PROTECTIVE EFFECT AGAINST AN EXPERIMENTAL INFECTION WITH SHIGELLA DYSENTERIAE

Phage-specific immunity impairs efficacy of bacteriophage targeting Vancomycin Resistant Enterococcus in a murine model

Bacteriophage therapy is a promising approach to address antimicrobial infections though questions remain regarding the impact of the immune response on clinical effectiveness. Here, we develop a mouse model to assess phage treatment using a cocktail of five phages from the Myoviridae and Siphoviridae families that target Vancomycin-Resistant Enterococcus gut colonization. Phage treatment significantly reduces fecal bacterial loads of Vancomycin-Resistant Enterococcus. We also characterize immune responses elicited following administration of the phage cocktail. While minimal innate responses are observed after phage administration, two rounds of treatment induces phage-specific neutralizing antibodies and accelerate phage clearance from tissues. Interestingly, the myophages in our cocktail induce a more robust neutralizing antibody response than the siphophages. This anti-phage immunity reduces the effectiveness of the phage cocktail in our murine model. Collectively, this study shows phage-specific immune responses may be an important consideration in the development of phage cocktails for therapeutic use.

Transmorphic phage-guided systemic delivery of TNFα gene for the treatment of human pediatric medulloblastoma

Medulloblastoma is the most common childhood brain tumor with an unfavorable prognosis and limited options of harmful treatments that are associated with devastating long-term side effects. Therefore, the development of safe, noninvasive, and effective therapeutic approaches is required to save the quality of life of young medulloblastoma survivors. We postulated that therapeutic targeting is a solution. Thus, we used a recently designed tumor-targeted bacteriophage (phage)-derived particle, named transmorphic phage/AAV, TPA, to deliver a transgene expressing the tumor necrosis factor-alpha (TNFα) for targeted systemic therapy of medulloblastoma. This vector was engineered to display the double-cyclic RGD4C ligand to selectively target tumors after intravenous administration. Furthermore, the lack of native phage tropism in mammalian cells warrants safe and selective systemic delivery to the tumor microenvironment. In vitro RGD4C.TPA.TNFα treatment of human medulloblastoma cells generated efficient and selective TNFα expression, subsequently triggering cell death. Combination with the chemotherapeutic drug cisplatin used clinically against medulloblastoma resulted in augmented effect through the enhancement of TNFα gene expression. Systemic administration of RGD4C.TPA.TNFα to mice-bearing subcutaneous medulloblastoma xenografts resulted in selective tumor homing of these particles and consequently, targeted tumor expression of TNFα, apoptosis, and destruction of the tumor vasculature. Thus, our RGD4C.TPA.TNFα particle provides selective and efficient systemic delivery of TNFα to medulloblastoma, yielding a potential TNFα anti-medulloblastoma therapy while sparing healthy tissues from the systemic toxicity of this cytokine.

Phage Interactions with the Nervous System in Health and Disease

The central nervous system manages all of our activities (e.g., direct thinking and decision-making processes). It receives information from the environment and responds to environmental stimuli. Bacterial viruses (bacteriophages, phages) are the most numerous structures occurring in the biosphere and are also found in the human organism. Therefore, understanding how phages may influence this system is of great importance and is the purpose of this review. We have focused on the effect of natural bacteriophages in the central nervous system, linking them to those present in the gut microbiota, creating the gut-brain axis network, as well as their interdependence. Importantly, based on the current knowledge in the field of phage application (e.g., intranasal) in the treatment of bacterial diseases associated with the brain and nervous system, bacteriophages may have significant therapeutic potential. Moreover, it was indicated that bacteriophages may influence cognitive processing. In addition, phages (via phage display technology) appear promising as a targeted therapeutic tool in the treatment of, among other things, brain cancers. The information collected and reviewed in this work indicates that phages and their impact on the nervous system is a fascinating and, so far, underexplored field. Therefore, the aim of this review is not only to summarize currently available information on the association of phages with the nervous system, but also to stimulate future studies that could pave the way for novel therapeutic approaches potentially useful in treating bacterial and non-bacterial neural diseases.

Reassessment of Historical Clinical Trials Supports the Effectiveness of Phage Therapy

Phage therapy has become a hot topic in medical research due to the increasing prevalence of antibiotic-resistant bacteria strains. In the treatment of bacterial infections, bacteriophages have several advantages over antibiotics, including strain specificity, lack of serious side effects, and low development costs. However, scientists dismissed the clinical success of early clinical trials in the 1940s, slowing the adoption of this promising antibacterial application in Western countries. The current study used statistical methods commonly used in modern meta-analysis to reevaluate early 20th-century studies and compare them with clinical trials conducted in the last 20 years. Using a random effect model, the development of disease after treatment with or without phages was measured in odds ratios (OR) with 95% confidence intervals (CI). Based on the findings of 17 clinical trials conducted between 1921 and 1940, phage therapy was effective (OR = 0.21, 95% CI = 0.10 to 0.44, P value < 0.0001). The current study includes a topic review on modern clinical trials; four could be analyzed, indicating a noneffective therapy (OR = 2.84, 95% CI = 1.53 to 5.27, P value = 0.0009). The results suggest phage therapy was surprisingly less effective than standard treatments in resolving bacterial infections. However, the results were affected by the small sample set size. This work also contextualizes the development of phage therapy in the early 20th century and highlights the expansion of phage applications in the last few years. In conclusion, the current review shows phage therapy is no longer an underestimated tool in the treatment of bacterial infections.

EGFR-targeted bacteriophage lambda penetrates model stromal and colorectal carcinoma tissues, is taken up into carcinoma cells, and interferes with 3-dimensional tumor formation

Introduction

Colorectal cancer and other adult solid cancers pose a significant challenge for successful treatment because the tumor microenvironment both hinders the action of conventional therapeutics and suppresses the immune activities of infiltrating leukocytes. The immune suppression is largely the effect of enhanced local mediators such as purine nucleosides and eicosanoids. Genetic approaches have the promise of interfering with these mechanisms of local immunosuppression to allow both intrinsic and therapeutic immunological anticancer processes. Bacterial phages offer a novel means of enabling access into tissues for therapeutic genetic manipulations.

Methods

We generated spheroids of fibroblastic and CRC cancer cells to model the 3-dimensional stromal and parenchymal components of colorectal tumours. We used these to examine the access and effects of both wildtype (WT) and epidermal growth factor (EGF)-presenting bacteriophage λ (WT- λ and EGF-λ) as a means of delivery of targeted genetic interventions in solid cancers. We used both confocal microscopy of spheroids exposed to AF488-tagged phages, and the recovery of viable phages as measured by plaque-forming assays to evaluate access; and measures of mitochondrial enzyme activity and cellular ATP to evaluate the outcome on the constituent cells.

Results

Using flourescence-tagged derivatives of these bacteriophages (AF488-WT-λ and AF488-EGF-λ) we showed that phage entry into these tumour microenvironments was possible and that the EGF ligand enabled efficient and persistent uptake into the cancer cell mass. EGF-λ became localized in the intracellular portion of cancer cells and was subjected to subsequent cellular processing. The targeted λ phage had no independent effect upon mature tumour spheroids, but interfered with the early formation and growth of cancer tissues without the need for addition of a toxic payload, suggesting that it might have beneficial effects by itself in addition to any genetic intervention delivered to the tumour. Interference with spheroid formation persisted over the duration of culture.

Discussion

We conclude that targeted phage technology is a feasible strategy to facilitate delivery into colorectal cancer tumour tissue (and by extension other solid carcinomas) and provides an appropriate delivery vehicle for a gene therapeutic that can reduce local immunosuppression and/or deliver an additional direct anticancer activity.

Proof-of-Concept Standardized Approach Using a Single-Disk Method Analogous to Antibiotic Disk Diffusion Assays for Routine Phage Susceptibility Testing in Diagnostic Laboratories

Application of bacteriophages is increasingly being implemented in clinical therapies. Prior susceptibility testing should be regarded as mandatory, but standards are lacking. The objective of this research was to develop a highly standardized methodology to facilitate phage susceptibility testing (PST) in clinical microbiology routine laboratories. Therefore, EUCAST methods established for single disk-based antibiotic susceptibility testing (AST) were adapted. In a first step, basic parameters were evaluated using well-studied Escherichia phage T4-Escherichia coli combinations. In addition, test results were compared to those from conventional spot test and efficiency of plating (EOP) approaches. In a second step, the applicability of the methodology and the most promising test parameters were demonstrated for five other frequently isolated clinical bacterial species and their corresponding phages. At present, the method predominantly leads to qualitative rather than quantitative results. This disk-based approach provides a standardized, easy-to-handle, reproducible and reliable PST protocol by relying on well-established routine procedures in diagnostic laboratories. IMPORTANCE Application of bacteriophages in clinical therapies is attractive due to increasing rates of isolation of multidrug-resistant bacteria worldwide. As the phage effect is highly specific, prior susceptibility testing of target bacteria is mandatory. Of note, established standards are lacking. In this research, we adapted the single-disk method for antibiotic susceptibility testing to phage susceptibility testing (PST) in order to provide a standardized, easy-to-handle, reproducible, and reliable PST protocol for application in diagnostic routine laboratories.

René Dubos, the Autochthonous Flora, and the Discovery of the Microbiome

Now characterised by high-throughput sequencing methods that enable the study of microbes without lab culture, the human "microbiome" (the microbial flora of the body) is said to have revolutionary implications for biology and medicine. According to many experts, we must now understand ourselves as "holobionts" like lichen or coral, multispecies superorganisms that consist of animal and symbiotic microbes in combination, because normal physiological function depends on them. Here I explore the 1960s research of biologist René Dubos, a forerunner figure mentioned in some historical accounts of the microbiome, and argue that he arrived at the superorganism concept 40 years before the Human Microbiome Project. This raises the question of why his contribution was not hailed as revolutionary at the time and why Dubos is not remembered for it.

Novel technologies to characterize and engineer the microbiome in inflammatory bowel disease

We present an overview of recent experimental and computational advances in technology used to characterize the microbiome, with a focus on how these developments improve our understanding of inflammatory bowel disease (IBD). Specifically, we present studies that make use of flow cytometry and metabolomics assays to provide a functional characterization of microbial communities. We also describe computational methods for strain-level resolution, temporal series, mycobiome and virome data, co-occurrence networks, and compositional data analysis. In addition, we review novel techniques to therapeutically manipulate the microbiome in IBD. We discuss the benefits and drawbacks of these technologies to increase awareness of specific biases, and to facilitate a more rigorous interpretation of results and their potential clinical application. Finally, we present future lines of research to better characterize the relation between microbial communities and IBD pathogenesis and progression.

Bacteriophages as Solid Tumor Theragnostic Agents

Cancer, especially the solid tumor sub-set, poses considerable challenges to modern medicine owing to the unique physiological characteristics and substantial variations in each tumor's microenvironmental niche fingerprints. Though there are many treatment methods available to treat solid tumors, still a considerable loss of life happens, due to the limitation of treatment options and the outcomes of ineffective treatments. Cancer cells evolve with chemo- or radiation-treatment strategies and later show adaptive behavior, leading to failed treatment. These challenges demand tailored and individually apt personalized treatment methods. Bacteriophages (or phages) and phage-based theragnostic vectors are gaining attention in the field of modern cancer medicine, beyond their bactericidal ability. With the invention of the latest techniques to fine-tune phages, such as in the field of genetic engineering, synthetic assembly methods, phage display, and chemical modifications, noteworthy progress in phage vector research for safe cancer application has been realized, including use in pre-clinical studies. Herein, we discuss the distinct fingerprints of solid tumor physiology and the potential for bacteriophage vectors to exploit specific tumor features for improvised tumor theragnostic applications.

Circadian Rhythm Modulation of Microbes During Health and Infection

Circadian rhythms, referring to 24-h daily oscillations in biological and physiological processes, can significantly regulate host immunity to pathogens, as well as commensals, resulting in altered susceptibility to disease development. Furthermore, vaccination responses to microbes have also shown time-of-day-dependent changes in the magnitude of protective immune responses elicited in the host. Thus, understanding host circadian rhythm effects on both gut bacteria and viruses during infection is important to minimize adverse effects on health and identify optimal times for therapeutic administration to maximize therapeutic success. In this review, we summarize the circadian modulations of gut bacteria, viruses and their interactions, both in health and during infection. We also discuss the importance of chronotherapy (i.e., time-specific therapy) as a plausible therapeutic administration strategy to enhance beneficial therapeutic responses.

Interactions of Bacteriophages with Animal and Human Organisms-Safety Issues in the Light of Phage Therapy

Bacteriophages are viruses infecting bacterial cells. Since there is a lack of specific receptors for bacteriophages on eukaryotic cells, these viruses were for a long time considered to be neutral to animals and humans. However, studies of recent years provided clear evidence that bacteriophages can interact with eukaryotic cells, significantly influencing the functions of tissues, organs, and systems of mammals, including humans. In this review article, we summarize and discuss recent discoveries in the field of interactions of phages with animal and human organisms. Possibilities of penetration of bacteriophages into eukaryotic cells, tissues, and organs are discussed, and evidence of the effects of phages on functions of the immune system, respiratory system, central nervous system, gastrointestinal system, urinary tract, and reproductive system are presented and discussed. Modulations of cancer cells by bacteriophages are indicated. Direct and indirect effects of virulent and temperate phages are discussed. We conclude that interactions of bacteriophages with animal and human organisms are robust, and they must be taken under consideration when using these viruses in medicine, especially in phage therapy, and in biotechnological applications.

Evaluating the potential efficacy and limitations of a phage for joint antibiotic and phage therapy of Staphylococcus aureus infections

This study explores the potential of a phage, PYO^Sa, for treating Staphylococcus aureus infections in combination with antibiotics. Population dynamic and genomic analysis identified a limitation and potential liability of using PYO^Sa for therapy. Due to the production of potentially pathogenic atypical small colony variants, PYO^Sa alone cannot eliminate S. aureus populations. However, we demonstrate that by following the administration of PYO^Sa with bactericidal antibiotics, this limitation and potential liability can be addressed. The methods used in this investigation to explore the efficacy of combinations of PYO^Sa and antibiotics for treating S. aureus infections can be employed to evaluate the clinical potential and facilitate the design of treatment protocols for any bacteria and phage that can be cultured in vitro.

In response to increasing frequencies of antibiotic-resistant pathogens, there has been a resurrection of interest in the use of bacteriophage to treat bacterial infections: phage therapy. Here we explore the potential of a seemingly ideal phage, PYO^Sa, for combination phage and antibiotic treatment of Staphylococcus aureus infections. This K-like phage has a broad host range; all 83 tested clinical isolates of S.aureus tested were susceptible to PYO^Sa. Because of the mode of action of PYO^Sa, S. aureus is unlikely to generate classical receptor-site mutants resistant to PYO^Sa; none were observed in the 13 clinical isolates tested. PYO^Sa kills S. aureus at high rates. On the downside, the results of our experiments and tests of the joint action of PYO^Sa and antibiotics raise issues that must be addressed before PYO^Sa is employed clinically. Despite the maintenance of the phage, PYO^Sa does not clear populations of S. aureus. Due to the ascent of a phenotyically diverse array of small-colony variants following an initial demise, the bacterial populations return to densities similar to that of phage-free controls. Using a combination of mathematical modeling and in vitro experiments, we postulate and present evidence for a mechanism to account for the demise–resurrection dynamics of PYO^Sa and S. aureus. Critically for phage therapy, our experimental results suggest that treatment with PYO^Sa followed by bactericidal antibiotics can clear populations of S. aureus more effectively than the antibiotics alone.

Recent progress towards the implementation of phage therapy in Western medicine

Like the sword of Damocles, the threat of a post-antibiotic era is hanging over humanity's head. The scientific and medical community is thus reconsidering bacteriophage therapy (BT) as a partial but realistic solution for treatment of difficult to eradicate bacterial infections. Here, we summarize the latest developments in clinical BT applications, with a focus on developments in the following areas: i) pharmacology of bacteriophages of major clinical importance and their synergy with antibiotics; ii) production of therapeutic phages; and iii) clinical trials, case studies, and case reports in the field. We address regulatory concerns, which are of paramount importance insofar as they dictate the conduct of clinical trials, which are needed for broader BT application. The increasing amount of new available data confirm the particularities of BT as being innovative and highly personalized. The current circumstances suggest that the immediate future of BT may be advanced within the framework of national BT centers in collaboration with competent authorities, which are urged to adopt incisive initiatives originally launched by some national regulatory authorities.

Basics for Improved Use of Phages for Therapy

Blood-borne therapeutic phages and phage capsids increasingly reach therapeutic targets as they acquire more persistence, i.e., become more resistant to non-targeted removal from blood. Pathogenic bacteria are targets during classical phage therapy. Metastatic tumors are potential future targets, during use of drug delivery vehicles (DDVs) that are phage derived. Phage therapy has, to date, only sometimes been successful. One cause of failure is low phage persistence. A three-step strategy for increasing persistence is to increase (1) the speed of lytic phage isolation, (2) the diversity of phages isolated, and (3) the effectiveness and speed of screening phages for high persistence. The importance of high persistence-screening is illustrated by our finding here of persistence dramatically higher for coliphage T3 than for its relative, coliphage T7, in murine blood. Coliphage T4 is more persistent, long-term than T3. Pseudomonas chlororaphis phage 201phi2-1 has relatively low persistence. These data are obtained with phages co-inoculated and separately assayed. In addition, highly persistent phage T3 undergoes dispersal to several murine organs and displays tumor tropism in epithelial tissue (xenografted human oral squamous cell carcinoma). Dispersal is an asset for phage therapy, but a liability for phage-based DDVs. We propose increased focus on phage persistence—and dispersal—screening.

Bacteriophages and the Immune System

Bacteriophages-viruses that infect bacteria-are abundant within our bodies, but their significance to human health is only beginning to be explored. Here, we synthesize what is currently known about our phageome and its interactions with the immune system. We first review how phages indirectly affect immunity via bacterial expression of phage-encoded proteins. We next review how phages directly influence innate immunity and bacterial clearance. Finally, we discuss adaptive immunity against phages and its implications for phage/bacterial interactions. In light of these data, we propose that our microbiome can be understood as an interconnected network of bacteria, bacteriophages, and human cells and that the stability of these tri-kingdom interactions may be important for maintaining our immunologic and metabolic health. Conversely, the disruption of this balance, through exposure to exogenous phages, microbial dysbiosis, or immune dysregulation, may contribute to disease. Expected final online publication date for the Annual Review of Virology, Volume 8 is September 2021. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

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.

Bacteriophage Therapy of Bacterial Infections: The Rediscovered Frontier

Antibiotic-resistant infections present a serious health concern worldwide. It is estimated that there are 2.8 million antibiotic-resistant infections and 35,000 deaths in the United States every year. Such microorganisms include Acinetobacter, Enterobacterioceae, Pseudomonas, Staphylococcus and Mycobacterium. Alternative treatment methods are, thus, necessary to treat such infections. Bacteriophages are viruses of bacteria. In a lytic infection, the newly formed phage particles lyse the bacterium and continue to infect other bacteria. In the early 20th century, d'Herelle, Bruynoghe and Maisin used bacterium-specific phages to treat bacterial infections. Bacteriophages are being identified, purified and developed as pharmaceutically acceptable macromolecular "drugs," undergoing strict quality control. Phages can be applied topically or delivered by inhalation, orally or parenterally. Some of the major drug-resistant infections that are potential targets of pharmaceutically prepared phages are Pseudomonas aeruginosa, Mycobacterium tuberculosis and Acinetobacter baumannii.

Crosstalk between circadian rhythms and the microbiota

Circadian rhythms influence daily molecular oscillations in gene/protein expression and aspects of biology and physiology, including behaviour, body temperature and sleep–wake cycles. These circadian rhythms have been associated with a number of metabolic, immune and microbial changes that correlate with health and susceptibility to disease, including infection. While light is the main inducer of circadian rhythms, other factors, including the microbiota, can have important effects on peripheral rhythms. The microbiota have been of significant interest to many investigators over the past decade, with the development of molecular techniques to identify large numbers of species and their function. These studies have shown microbial associations with disease susceptibility, and some of these have demonstrated that alterations in microbiota cause disease. Microbial circadian oscillations impact host metabolism and immunity directly and indirectly. Interestingly, microbial oscillations also regulate host circadian rhythms, and the host circadian rhythms in turn modulate microbial composition. Thus, it is of considerable interest and importance to understand the crosstalk between circadian rhythms and microbiota and especially the microbial influences on the host. In this review, we aim to discuss the role of circadian microbial oscillations and how they influence host immunity. In addition, we discuss how host circadian rhythms can also modulate microbial rhythms. We also discuss potential connections between microbes and circadian rhythms and how these may be used therapeutically to maximize clinical success.

Bacteriophages Improve Outcomes in Experimental Staphylococcus aureus Ventilator-associated Pneumonia

Rationale: Infections caused by multidrug-resistant bacteria are a major clinical challenge. Phage therapy is a promising alternative antibacterial strategy.Objectives: To evaluate the efficacy of intravenous phage therapy for the treatment of ventilator-associated pneumonia due to methicillin-resistant Staphylococcus aureus in rats.Methods: In a randomized, blinded, controlled experimental study, we compared intravenous teicoplanin (3 mg/kg, n = 12), a cocktail of four phages (2-3 × 10⁹ plaque-forming units/ml of 2003, 2002, 3A, and K; n = 12), and a combination of both (n = 11) given 2, 12, and 24 hours after induction of pneumonia, and then once daily for 4 days. The primary outcome was survival at Day 4. Secondary outcomes were bacterial and phage densities in lungs and spleen, histopathological scoring of infection within the lungs, and inflammatory biomarkers in blood.Measurements and Main Results: Treatment with either phages or teicoplanin increased survival from 0% to 58% and 50%, respectively (P < 0.005). The combination of phages and antibiotics did not further improve outcomes (45% survival). Animal survival correlated with reduced bacterial burdens in the lung (1.2 × 10⁶ cfu/g of tissue for survivors vs. 1.2 × 10⁹ cfu/g for nonsurviving animals; P < 0.0001), as well as improved histopathological outcomes. Phage multiplication within the lung occurred during treatment. IL-1β increased in all treatment groups over the course of therapy.Conclusions: Phage therapy was as effective as teicoplanin in improving survival and decreasing bacterial load within the lungs of rats infected with methicillin-resistant S. aureus. Combining antibiotics with phage therapy did not further improve outcomes.

Therapeutic bacteriophages as a rescue treatment for drug-resistant infections - an in vivo studies overview

Bacteriophages, highly prevalent in all environments, have found their use in medicine as an alternative or complement to antibiotics. The therapeutic use of bacteriophages was particularly popular in the 1920s and 1930s, until the discovery and introduction of antibiotics. Due to the dynamic growth of antibiotic resistance among bacterial strains, numerous international institutions (such as the FDA) have declared the search for novel treatment modalities to be of the highest priority. To date, bacteriophage therapy has not been registered for general use in Western countries. The regulation of biological medicinal products (within medicinal product regulation) does not contain a specific documentation frame for bacteriophages (only for vaccines, blood derived products, etc.) which, as active substances, need to meet specific requirements. Recently, the FDA allowed bacteriophage therapy to be used in the United States, via the Emergency Investigational New Drug scheme; clinical trials to compare the safety and efficacy of bacteriophage therapy are also permitted. To date, several therapeutic products of this type have made it to phase I or II; some clinical programmes have also been completed. This article cites numerous animal model studies and registered clinical trials, showing the safety and effectiveness of bacteriophage therapy, including infections caused by bacterial strains resistant to antibiotic treatment.

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.

The dawn of phage therapy

Bacteriophages or phages, being the most abundant entities on earth, represent a potential solution to a diverse range of problems. Phages are successful antibacterial agents whose use in therapeutics was hindered by the discovery of antibiotics. Eventually, because of the development and spread of antibiotic resistance among most bacterial species, interest in phage as therapeutic entities has returned, because their noninfectious nature to humans should make them safe for human nanomedicine. This review highlights the most recent advances and progress in phage therapy and bacterial hosts against which phage research is currently being conducted with respect to food, human, and marine pathogens. Bacterial immunity against phages and tactics of phage revenge to defeat bacterial defense systems are also summarized. We have also discussed approved phage-based products (whole phage-based products and phage proteins) and shed light on their influence on the eukaryotic host with respect to host safety and induction of immune response against phage preparations. Moreover, creation of phages with desirable qualities and their uses in cancer treatment, vaccine production, and other therapies are also reviewed to bring together evidence from the scientific literature about the potentials and possible utility of phage and phage encoded proteins in the field of therapeutics and industrial biotechnology.

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.

Efficacy of systemic temozolomide-activated phage-targeted gene therapy in human glioblastoma

Glioblastoma multiforme (GBM) is the most lethal primary intracranial malignant neoplasm in adults and most resistant to treatment. Integration of gene therapy and chemotherapy, chemovirotherapy, has the potential to improve treatment. We have introduced an intravenous bacteriophage (phage) vector for dual targeting of therapeutic genes to glioblastoma. It is a hybrid AAV/phage, AAVP, designed to deliver a recombinant adeno-associated virus genome (rAAV) by the capsid of M13 phage. In this vector, dual tumor targeting is first achieved by phage capsid display of the RGD4C ligand that binds the αvβ3 integrin receptor. Second, genes are expressed from a tumor-activated and temozolomide (TMZ)-induced promoter of the glucose-regulated protein, Grp78 Here, we investigated systemic combination therapy using TMZ and targeted suicide gene therapy by the RGD4C/AAVP-Grp78 Firstly, in vitro we showed that TMZ increases endogenous Grp78 gene expression and boosts transgene expression from the RGD4C/AAVP-Grp78 in human GBM cells. Next, RGD4C/AAVP-Grp78 targets intracranial tumors in mice following intravenous administration. Finally, combination of TMZ and RGD4C/AAVP-Grp78 targeted gene therapy exerts a synergistic effect to suppress growth of orthotopic glioblastoma.

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.

A bacteriophages journey through the human body

The human body is colonized by a diverse collective of microorganisms, including bacteria, fungi, protozoa and viruses. The smallest entity of this microbial conglomerate are the bacterial viruses. Bacteriophages, or phages for short, exert significant selective pressure on their bacterial hosts, undoubtedly influencing the human microbiome and its impact on our health and well-being. Phages colonize all niches of the body, including the skin, oral cavity, lungs, gut, and urinary tract. As such our bodies are frequently and continuously exposed to diverse collections of phages. Despite the prevalence of phages throughout our bodies, the extent of their interactions with human cells, organs, and immune system is still largely unknown. Phages physically interact with our mucosal surfaces, are capable of bypassing epithelial cell layers, disseminate throughout the body and may manipulate our immune system. Here, I establish the novel concept of an "intra-body phageome," which encompasses the collection of phages residing within the classically "sterile" regions of the body. This review will take a phage-centric view of the microbiota, human body, and immune system with the ultimate goal of inspiring a greater appreciation for both the indirect and direct interactions between bacteriophages and their mammalian hosts.

Bacteriophage research - What we have learnt and what still needs to be addressed

Research on bacteriophages has significantly enhanced our understanding of molecular biology, the genomes of prokaryotic cells, and viral ecology. Phages and lysins offer a viable alternative to the declining utility of antibiotics in this post-antibiotic era. They also provide ideal teaching tools for genomics and bioinformatics. This article touches on the first 100 years of phage research with the author commenting on what he thinks are the highlights, and what needs to be addressed.

Phage Therapy for a Multidrug-Resistant Acinetobacter baumannii Craniectomy Site Infection

In the era of antibiotic resistance, alternative treatment options for multidrug-resistant bacterial infections are being explored. We present a case of multidrug-resistant Acinetobacter baumannii infection treated with bacteriophages. Clinical trials are needed to further investigate bacteriophage therapy as an option to treat multidrug-resistant bacterial infections.

Applications for Bacteriophage Therapy during Pregnancy and the Perinatal Period

Pregnant women and their unborn children are a population that is particularly vulnerable to bacterial infection. Physiological changes that occur during pregnancy affect the way women respond to such infections and the options that clinicians have for treatment. Antibiotics are still considered the best option for active infections and a suitable prophylaxis for prevention of potential infections, such as vaginal/rectal Streptococcus agalactiae colonization prior to birth. The effect of such antibiotic use on the developing fetus, however, is still largely unknown. Recent research has suggested that the fetal gut microbiota plays a critical role in fetal immunologic programming. Hence, even minor alterations in this microbiota may have potentially significant downstream effects. An ideal antibacterial therapeutic for administration during pregnancy would be one that is highly specific for its target, leaving the surrounding microbiota intact. This review first provides a basic overview of the challenges a clinician faces when administering therapeutics to a pregnant patient and then goes on to explore common bacterial infections in pregnancy, use of antibiotics for treatment/prevention of such infections and the consequences of such treatment for the mother and infant. With this background established, the review then explores the potential for use of bacteriophage (phage) therapy as an alternative to antibiotics during the antenatal period. Many previous reviews have highlighted the revitalization of and potential for phage therapy for treatment of a range of bacterial infections, particularly in the context of the increasing threat of widespread antibiotic resistance. However, information on the potential for the use of phage therapeutics in pregnancy is lacking. This review aims to provide a thorough overview of studies of this nature and discuss the feasibility of bacteriophage use during pregnancy to treat and/or prevent bacterial infections.

Internalization of a polysialic acid-binding Escherichia coli bacteriophage into eukaryotic neuroblastoma cells

Eukaryotic organisms are continuously exposed to bacteriophages, which are efficient gene transfer agents in bacteria. However, bacteriophages are considered not to pass the eukaryotic cell membrane and enter nonphagocytic cells. Here we report the binding and penetration of Escherichia coli PK1A2 bacteriophage into live eukaryotic neuroblastoma cells in vitro. The phage interacts with cell surface polysialic acid, which shares structural similarity with the bacterial phage receptor. Using fluorescence and electron microscopy, we show that phages are internalized via the endolysosomal route and persist inside the human cells up to one day without affecting cell viability. Phage capsid integrity is lost in lysosomes, and the phage DNA is eventually degraded. We did not detect the entry of phage DNA into the nucleus; however, we speculate that this might occur as a rare event, and propose that this potential mechanism could explain prokaryote–eukaryote gene flow.

Eukaryotic organisms are continuously exposed to bacteriophages, but these are not thought to enter non-phagocytic cells. Here, Lehti et al. show that a bacteriophage can bind to a specific receptor on the surface of human neuroblastoma cells in vitro, and be internalized via the endolysosomal route.

Bacteriophage Transcytosis Provides a Mechanism To Cross Epithelial Cell Layers

Bacterial viruses are among the most numerous biological entities within the human body. These viruses are found within regions of the body that have conventionally been considered sterile, including the blood, lymph, and organs. However, the primary mechanism that bacterial viruses use to bypass epithelial cell layers and access the body remains unknown. Here, we used in vitro studies to demonstrate the rapid and directional transcytosis of diverse bacteriophages across confluent cell layers originating from the gut, lung, liver, kidney, and brain. Bacteriophage transcytosis across cell layers had a significant preferential directionality for apical-to-basolateral transport, with approximately 0.1% of total bacteriophages applied being transcytosed over a 2-h period. Bacteriophages were capable of crossing the epithelial cell layer within 10 min with transport not significantly affected by the presence of bacterial endotoxins. Microscopy and cellular assays revealed that bacteriophages accessed both the vesicular and cytosolic compartments of the eukaryotic cell, with phage transcytosis suggested to traffic through the Golgi apparatus via the endomembrane system. Extrapolating from these results, we estimated that 31 billion bacteriophage particles are transcytosed across the epithelial cell layers of the gut into the average human body each day. The transcytosis of bacteriophages is a natural and ubiquitous process that provides a mechanistic explanation for the occurrence of phages within the body.

Bacteriophages (phages) are viruses that infect bacteria. They cannot infect eukaryotic cells but can penetrate epithelial cell layers and spread throughout sterile regions of our bodies, including the blood, lymph, organs, and even the brain. Yet how phages cross these eukaryotic cell layers and gain access to the body remains unknown. In this work, epithelial cells were observed to take up and transport phages across the cell, releasing active phages on the opposite cell surface. Based on these results, we posit that the human body is continually absorbing phages from the gut and transporting them throughout the cell structure and subsequently the body. These results reveal that phages interact directly with the cells and organs of our bodies, likely contributing to human health and immunity.

Phage Therapy in a 16-Year-Old Boy with Netherton Syndrome

Netherton syndrome (NS) is a rare autosomal recessive disorder, characterized by a classical triad of clinical features, including congenital ichthyosiform erythroderma, trichorrhexis invaginata, and atopic diathesis coupled with frequent bacterial infections (1). The genetic basis for the disease has been recently identified with mutations in gene SPINK5, which is involved in the regulation of formation of skin barriers. We report on a 16-year-old male with all the typical manifestations of NS, including atopic diathesis and ongoing serious staphylococcal infections and allergy to multiple antibiotics whose family sought help at the Eliava Phage Therapy Center when all other treatment options were failing. Treatment with several antistaphylococcal bacteriophage preparations led to significant improvement within 7 days and very substantial changes in his symptoms and quality of life after treatment for 6 months, including return visits to the Eliava Phage Therapy Center after 3 and 6 months of ongoing use of phage at home.

Bacteriophage Procurement for Therapeutic Purposes

Bacteriophages (phages), discovered 100 years ago, are able to infect and destroy only bacterial cells. In the current crisis of antibiotic efficacy, phage therapy is considered as a supplementary or even alternative therapeutic approach. Evolution of multidrug-resistant and pandrug-resistant bacterial strains poses a real threat, so it is extremely important to have the possibility to isolate new phages for therapeutic purposes. Our phage laboratory and therapy center has extensive experience with phage isolation, characterization, and therapeutic application. In this article we present current progress in bacteriophages isolation and use for therapeutic purposes, our experience in this field and its practical implications for phage therapy. We attempt to summarize the state of the art: properties of phages, the methods for their isolation, criteria of phage selection for therapeutic purposes and limitations of their use. Perspectives for the use of genetically engineered phages to specifically target bacterial virulence-associated genes are also briefly presented.

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.

Bacteriophage application to control the contaminated water with Shigella

Shigella is one of the most important waterborne and foodborne pathogens around the world. Emergence of antibiotic-resistant Shigella has made the development of alternatives to conventional antibiotics necessary. In this study, a virulent Myoviridae bacteriophage, pSs-1 was isolated from environmental water in South Korea and showed infectivity to S. flexneri as well as S. sonnei strains. One-step growth analysis showed that pSs-1 has a short latent period (25 min) and a large burst size (97 PFU/cell). According to the genomic analysis, pSs-1 contains 164,999 bp of genome with a G + C content of 35.54% and it is considered as a member of the T4-like bacteriophage group. These results showed that pSs-1 may have potential as a biocontrol agent instead of conventional antibiotics for shigellosis.

Safety and efficacy of phage therapy via the intravenous route

Increasing development of antimicrobial resistance is driving a resurgence in interest in phage therapy: the use of bacteriophages to treat bacterial infections. As the lytic action of bacteriophages is unaffected by the antibiotic resistance status of their bacterial target, it is thought that phage therapy may have considerable potential in the treatment of a wide range of topical and localized infections. As yet this interest has not extended to intravenous (IV) use, which is surprising given that the historical record shows that phages are likely to be safe and effective when delivered by this route. Starting almost 100 years ago, phages were administered intravenously in treatment of systemic infections including typhoid, and Staphylococcal bacteremia. There was extensive IV use of phages in the 1940s to treat typhoid, reportedly with outstanding efficacy and safety. The safety of IV phage administration is also underpinned by the detailed work of Ochs and colleagues in Seattle who have over four decades' experience with IV injection into human subjects of large doses of highly purified coliphage PhiX174. Though these subjects included a large number of immune-deficient children, no serious side effects were observed over this extended time period. The large and continuing global health problems of typhoid and Staphylococcus aureus are exacerbated by the increasing antibiotic resistance of these pathogens. We contend that these infections are excellent candidates for use of IV phage therapy.

Characterization and complete genome sequence of a novel N4-like bacteriophage, pSb-1 infecting Shigella boydii

Shigellosis is one of major foodborne pathogens in both developed and developing countries. Although antibiotic therapy is considered an effective treatment for shigellosis, the imprudent use of antibiotics has led to the increase of multiple-antibiotic-resistant Shigella species globally. In this study, we isolated a virulent Podoviridae bacteriophage (phage), pSb-1, that infects Shigella boydii. One-step growth analysis revealed that this phage has a short latent period (15 min) and a large burst size (152.63 PFU/cell), indicating that pSb-1 has good host infectivity and effective lytic activity. The double-stranded DNA genome of pSb-1 is composed of 71,629 bp with a G + C content of 42.74%. The genome encodes 103 putative ORFs, 9 putative promoters, 21 transcriptional terminators, and one tRNA region. Genome sequence analysis of pSb-1 and comparative analysis with the homologous phage EC1-UPM, N4-like phage revealed that there is a high degree of similarity (94%, nucleotide sequence identity) between pSb-1 and EC1-UPM in 73 of the 103 ORFs of pSb-1. The results of this investigation indicate that pSb-1 is a novel virulent N4-like phage infecting S. boydii and that this phage might have potential uses against shigellosis.

Use of bacteriophages in the treatment of Pseudomonas aeruginosa infections

Phage therapy for Pseudomonas aeruginosa infections has been used for more than 50 years. Controlled investigation into its use dates from the early 1990s when positive laboratory studies of local and systemic infection were followed by clinical studies: symptomatic improvement and phage multiplication were seen in a pet dog with otitis and a human with an infected burn. Antibiotic resistance has renewed interest in this approach. There have been recent positive reports in the treatment of experimental animal infection including systemic and respiratory infections. Phages have shown promise against experimental biofilms. Two small recent clinical trials in otitis, of dogs and of human patients have provided some encouraging results. Phage has potential in the treatment of antibiotic resistant infection by P. aeruginosa. Hence, full scale clinical trials are needed.

Therapeutic and prophylactic applications of bacteriophage components in modern medicine

As the interactions of phage with mammalian innate and adaptive immune systems are better delineated and with our ability to recognize and eliminate toxins and other potentially harmful phage gene products, the potential of phage therapies is now being realized. Early efforts to use phage therapeutically were hampered by inadequate phage purification and limited knowledge of phage-bacterial and phage-human relations. However, although use of phage as an antibacterial therapy in countries that require controlled clinical studies has been hampered by the high costs of patient trials, their use as vaccines and the use of phage components such as lysolytic enzymes or lysozymes has progressed to the point of commercial applications. Recent studies concerning the intimate associations between mammalian hosts and bacterial and phage microbiomes should hasten this progress.

Characterization and complete genome sequence of the Shigella bacteriophage pSf-1

Shigellosis is a global health problem, and Shigella flexneri is the major cause of this disease. In this study, we isolated a virulent Siphoviridae bacteriophage (phage), pSf-1, that infects S. flexneri. This phage was isolated from the Han River in Korea and was found to infect S. flexneri, Shigella boydii, and Shigella sonnei. One-step growth analysis revealed that this phage has a short latent period (10 min) and a large burst size (86.86 PFU/cell), indicating that pSf-1 has good host infectivity and effective lytic activity. The double-stranded DNA genome of pSf-1 is composed of 51,821 bp with a G + C content of 44.02%. The genome encodes 94 putative ORFs, 71 putative promoters, and 60 transcriptional terminator regions. Genome sequence analysis of pSf-1 and comparative analysis with the homologous Shigella phage Shfl1 revealed that there is a high degree of similarity between pSf-1 and Shfl1 in 54 of the 94 ORFs of pSf-1. The results of this investigation indicate that pSf-1 is a novel Shigella phage and that this phage might have potential uses against shigellosis.

Bacteriophages for managing Shigella in various clinical and non-clinical settings

The control of shigellosis in humans enjoys a prominent position in the history of bacteriophage therapy. d’Herelle first demonstrated the efficacy of phage therapy by curing 4 patients of shigellosis, and several subsequent studies confirmed the ability of phages to reduce Shigella based infection. Shigella spp continue to cause millions of illnesses and deaths each year and the use of phages to control the disease in humans and the spread of the bacteria within food and water could point the way forward to the effective management of an infectious disease with global influence.

Propionibacterium acnes bacteriophages display limited genetic diversity and broad killing activity against bacterial skin isolates

Investigation of the human microbiome has revealed diverse and complex microbial communities at distinct anatomic sites. The microbiome of the human sebaceous follicle provides a tractable model in which to study its dominant bacterial inhabitant, Propionibacterium acnes, which is thought to contribute to the pathogenesis of the human disease acne. To explore the diversity of the bacteriophages that infect P. acnes, 11 P. acnes phages were isolated from the sebaceous follicles of donors with healthy skin or acne and their genomes were sequenced. Comparative genomic analysis of the P. acnes phage population, which spans a 30-year temporal period and a broad geographic range, reveals striking similarity in terms of genome length, percent GC content, nucleotide identity (>85%), and gene content. This was unexpected, given the far-ranging diversity observed in virtually all other phage populations. Although the P. acnes phages display a broad host range against clinical isolates of P. acnes, two bacterial isolates were resistant to many of these phages. Moreover, the patterns of phage resistance correlate closely with the presence of clustered regularly interspaced short palindromic repeat elements in the bacteria that target a specific subset of phages, conferring a system of prokaryotic innate immunity. The limited diversity of the P. acnes bacteriophages, which may relate to the unique evolutionary constraints imposed by the lipid-rich anaerobic environment in which their bacterial hosts reside, points to the potential utility of phage-based antimicrobial therapy for acne.

IMPORTANCE

Propionibacterium acnes is a dominant member of the skin microflora and has also been implicated in the pathogenesis of acne; however, little is known about the bacteriophages that coexist with and infect this bacterium. Here we present the novel genome sequences of 11 P. acnes phages, thereby substantially increasing the amount of available genomic information about this phage population. Surprisingly, we find that, unlike other well-studied bacteriophages, P. acnes phages are highly homogeneous and show a striking lack of genetic diversity, which is perhaps related to their unique and restricted habitat. They also share a broad ability to kill clinical isolates of P. acnes; phage resistance is not prevalent, but when detected, it appears to be conferred by chromosomally encoded immunity elements within the host genome. We believe that these phages display numerous features that would make them ideal candidates for the development of a phage-based therapy for acne.

Phage therapy: delivering on the promise

Bacteriophages are viruses that infect and, in many cases, destroy their bacterial targets. Within a few years of their initial discovery they were being investigated as therapeutic agents for infectious disease, an approach known as phage therapy. However, the nature of these exquisitely specific agents was not understood and much early use was both uninformed and unsuccessful. As a result they were replaced by chemical antibiotics once these became available. Although work on phage therapy continued (and continues) in Eastern Europe, this was not conducted to a standard allowing it to support clinical uses in areas regulated by the European Medicines Agency or the US FDA. To develop phage therapy for these areas requires work carried out in accordance with the requirements of these agencies, and, driven by the current crisis of antibiotic resistance, such clinical trials are now under way. The first Phase I clinical trial of safety was reported in 2005, and the results of the first Phase II clinical trial of efficacy of a bacteriophage therapeutic was published in 2009. While the delivery of these relatively large and complex agents to the site of disease can be more challenging than for conventional, small-molecule antibiotics, bacteriophages are then able to multiply locally even from an extremely low (picogram range) initial dose. This multiplication where and only where they are needed underlies the potential for bacteriophage therapeutics to become a much needed and powerful weapon against bacterial disease.

Efficacy of bacteriophage therapy in experimental sepsis and meningitis caused by a clone O25b:H4-ST131 Escherichia coli strain producing CTX-M-15

We evaluated phage therapy in experimental infections due to S242, a fatal neonatal meningitis Escherichia coli strain belonging to the worldwide-distributed O25b:H4-ST131 clone that produces extended-spectrum beta-lactamase CTX-M-15. A lytic phage, EC200(PP), active against S242, was isolated from environmental water. After determining in vitro and ex vivo stabilities and pharmacokinetic properties of EC200(PP) in rat pups, we assessed the therapeutic efficacy of a single dose of 10(8) PFU using models of sepsis and meningitis in which fatality was 100%. EC200(PP) was partially neutralized by human serum. In contrast to the high concentration of phage in the spleen and the kidney, low titers in urine and the central nervous system were observed. Nevertheless, in the sepsis model, EC200(PP) administered 7 h or 24 h postinfection resulted in 100% and 50% pup survival, respectively. In the meningitis model, EC200(PP) administered 1 h or 7 h postinfection rescued 100% of the animals. The most delayed treatments were associated with the selection of phage-resistant S242 mutants. However, a representative mutant was highly sensitive to killing serum activity and avirulent in an animal model. EC200(PP) is a potential therapeutic agent for sepsis and meningitis caused by the widespread E. coli O25:H4-ST131 multidrug-resistant clone.