Modeling the synergistic elimination of bacteria by phage and the innate immune system

Extreme diversity of phage amplification rates and phage-antibiotic interactions revealed by PHORCE

Growth rate plays a fundamental role in microbiology and serves as an important proxy for fitness in evolution. While high-throughput measurements of bacterial growth rates are easily performed in any microbiology laboratory, similar methods are lacking for bacteriophages. This gap hinders systematic comparisons of important phage phenotypes, such as their amplification rate in bacterial populations and their bactericidal effect, across different phages and environmental conditions. Here, we show that the amplification rate of lytic phages can be quantified by analyzing bacterial population growth and collapse dynamics under phage predation using a parsimonious mathematical model - an approach termed Phage-Host Observation for Rate estimation from Collapse Events (PHORCE). We found that the resulting phage amplification rate captures the bactericidal effect independent of initial phage and bacterial population sizes for fast-growing hosts and adsorption-limited phages. Using high-throughput PHORCE, we found that the amplification rates of Escherichia coli phages vary widely by more than three orders of magnitude. Furthermore, our approach suggests that phage-antibiotic interactions are predominantly determined by the antibiotic, and not by the phage. In particular, the ribosome-inhibiting antibiotic doxycycline generally showed antagonism with phage amplification, whereas the DNA-damaging antibiotic nitrofurantoin was synergistic. This framework provides a means to quantitatively characterize phage phenotypes and may facilitate future high-throughput phage screens for antibacterial applications.

Combating Antibiotic Resistance: Mechanisms, Multidrug-Resistant Pathogens, and Novel Therapeutic Approaches: An Updated Review

The escalating global health crisis of antibiotic resistance, driven by the rapid emergence of multidrug-resistant (MDR) bacterial pathogens, necessitates urgent and innovative countermeasures. This review comprehensively examines the diverse mechanisms employed by bacteria to evade antibiotic action, including alterations in cell membrane permeability, efflux pump overexpression, biofilm formation, target site modifications, and the enzymatic degradation of antibiotics. Specific focus is given to membrane transport systems such as ATP-binding cassette (ABC) transporters, resistance-nodulation-division (RND) efflux pumps, major facilitator superfamily (MFS) transporters, multidrug and toxic compound extrusion (MATE) systems, small multidrug resistance (SMR) families, and proteobacterial antimicrobial compound efflux (PACE) families. Additionally, the review explores the global burden of MDR pathogens and evaluates emerging therapeutic strategies, including quorum quenching (QQ), probiotics, postbiotics, synbiotics, antimicrobial peptides (AMPs), stem cell applications, immunotherapy, antibacterial photodynamic therapy (aPDT), and bacteriophage. Furthermore, this review discusses novel antimicrobial agents, such as animal-venom-derived compounds and nanobiotics, as promising alternatives to conventional antibiotics. The interplay between clustered regularly interspaced short palindromic repeats (CRISPR) and CRISPR-associated proteins (Cas) in bacterial adaptive immunity is analyzed, revealing opportunities for targeted genetic interventions. By synthesizing current advancements and emerging strategies, this review underscores the necessity of interdisciplinary collaboration among biomedical scientists, researchers, and the pharmaceutical industry to drive the development of novel antibacterial agents. Ultimately, this comprehensive analysis provides a roadmap for future research, emphasizing the urgent need for sustainable and cooperative approaches to combat antibiotic resistance and safeguard global health.

Crossing the Chasm: How to Approach Translational Pharmacokinetic-Pharmacodynamic Modeling of Phage Dosing

Effectively treating multidrug-resistant bacterial infections remains challenging due to the limited drug development pipeline and a scarcity of novel agents effective against these highly resistant pathogens. Bacteriophages (phages) are a potential addition to the antimicrobial treatment arsenal. Though, phages are currently being tested in clinical trials for antibiotic-resistant infections, phages lack a fundamental understanding of optimal dosing in humans. Rationally designed preclinical studies using in vitro and in vivo infection models, allow us to assess clinically relevant phage +/- antibiotic exposure (pharmacokinetics), the resulting treatment impact on the infecting pathogen (pharmacodynamics) and host immune response (immunodynamics). A mechanistic modeling framework allows us to integrate this knowledge gained from preclinical studies to develop predictive models. We reviewed recently published mathematical models based on in vitro and/or in vivo data that evaluate the effects of varying bacterial or phage densities, phage characteristics (burst size, adsorption rate), phage pharmacokinetics, phage-antibiotic combinations and host immune responses. In our review, we analyzed study designs and the data used to inform the development of these mechanistic models. Insights gained from model-based simulations were reviewed as they help identify crucial phage parameters for determining effective phage dosing. These efforts contribute to bridging the gap between phage therapy research and its clinical translation.

Characterization of two Friunavirus phages and their inhibitory effects on biofilms of extremely drug resistant Acinetobacter baumannii in Dakar, Senegal

BACKGROUND

Acinetobacter baumannii is a gram-negative, opportunistic pathogen, that is responsible for a wide variety of infections and is a significant cause of hospital-acquired infections. A. baumannii is listed by the World Health Organization (WHO) as a critical priority pathogen because of its high level of antibiotic resistance and the urgent need for alternative treatment solutions. To address this challenge, bacteriophages have been used to combat bacterial infections for more than a century, and phage research has regained interest in recent years due to antimicrobial resistance (AMR). However, although the vast majority of deaths from the AMR crisis will occur in developing countries in Africa and Asia, few phages' studies have been conducted in these regions. In this study, we present a comprehensive characterization of the bacteriophages vAbBal23 and vAbAbd25, actives against extremely drug-resistant (XDR) A. baumannii.

METHODS

Phages were isolated from environmental wastewaters in Dakar, Senegal. The host-range, thermal and pH stabilities, infection kinetics, one step growth assay, antibiofilm activity assay, sequencing, and genomic analysis, were performed to characterize the isolated phages.

RESULTS

Comparative genomic and phylogenetic analyses revealed that vAbBal23 and vAbAbd25 belong to the Caudoviricetes class, Autographiviridae family and Friunavirus genus. Both phages demonstrated activity against strains with capsular type KL230. They were stable over a wide pH range (pH 3 to 9) and at temperatures ranging from 25 °C to 40 °C. Additionally, the phages exhibited notable activity against both planktonic and biofilm cells of targeted extremely drug resistant A. baumannii. The results presented here indicate the lytic nature of vAbBal23 and vAbAbd25. This is further supported by the absence of genes encoding toxins, resistance genes and bacterial virulence factors, highlighting their potential for future phage applications.

CONCLUSION

Phages vAbBal23 and vAbAbd25 are promising biological agents that can infect A. baumannii, making them suitable candidates for use in phage therapies.

Application of MIDD to accelerate the development of anti-infectives: Current status and future perspectives

This review examines the role of model-informed drug development (MIDD) in advancing antibacterial and antiviral drug development, with an emphasis on the inclusion of host system dynamics into modeling efforts. Amidst the growing challenges of multidrug resistance and diminishing market returns, innovative methodologies are crucial for continuous drug discovery and development. The MIDD approach, with its robust capacity to integrate diverse data types, offers a promising solution. In particular, the utilization of appropriate modeling and simulation techniques for better characterization and early assessment of drug resistance are discussed. The evolution of MIDD practices across different infectious disease fields is also summarized, and compared to advancements achieved in oncology. Moving forward, the application of MIDD should expand into host system dynamics as these considerations are critical for the development of "live drugs" (e.g. chimeric antigen receptor T cells or bacteriophages) to address issues like antibiotic resistance or latent viral infections.

Klebsiella pneumoniae infections and phage therapy

OBJECTIVE

Carbapenem-colistin-resistant Klebsiella pneumoniae has emerged as a serious global problem. Klebsiella pneumoniae is a major culprit in healthcare settings and is responsible for septicemia, urinary tract infections, pneumonia, meningitis, burn wound and surgical site infections, and liver abscesses even in younger and healthier population worldwide. The formation of biofilm prevents antibiotics from reaching the bacteria and exerting their effector mechanism. The non-availability of therapeutic alternatives (antibiotic therapy) further complicates the scenario. However, in the era of antibiotic resistance, bacteriophage therapy emerges as a ray of hope against antibiotic-resistant bacteria.

METHOD

The present review focuses on the therapeutic potential of bacteriophages as an antimicrobial agent with special reference to safety, specificity, efficacy, dosage, and dosage frequency against Pan-Drug Resistant (PDR) K. pneumoniae, both in-vitro and in-vivo (animals and human) studies.

RESULT

This review highlights the perspectives therapeutic potential of bacteriophages, their impact on the host immune system, combination therapy, and bacteriophage-encoded gene product endolysin, artificial lysins (Artilysins), polysaccharide depolymerase, and peptidoglycan hydrolases.

CONCLUSION

This review briefly describes the application of bacteriophage and its encoded gene products in clinical trials.

Metapopulation model of phage therapy of an acute Pseudomonas aeruginosa lung infection

Infections caused by multidrug resistant (MDR) pathogenic bacteria are a global health threat. Bacteriophages ("phage") are increasingly used as alternative or last-resort therapeutics to treat patients infected by MDR bacteria. However, the therapeutic outcomes of phage therapy may be limited by the emergence of phage resistance during treatment and/or by physical constraints that impede phage-bacteria interactions in vivo. In this work, we evaluate the role of lung spatial structure on the efficacy of phage therapy for Pseudomonas aeruginosa infections. To do so, we developed a spatially structured metapopulation network model based on the geometry of the bronchial tree, including host innate immune responses and the emergence of phage-resistant bacterial mutants. We model the ecological interactions between bacteria, phage, and the host innate immune system at the airway (node) level. The model predicts the synergistic elimination of a P. aeruginosa infection due to the combined effects of phage and neutrophils, given the sufficient innate immune activity and efficient phage-induced lysis. The metapopulation model simulations also predict that MDR bacteria are cleared faster at distal nodes of the bronchial tree. Notably, image analysis of lung tissue time series from wild-type and lymphocyte-depleted mice revealed a concordant, statistically significant pattern: infection intensity cleared in the bottom before the top of the lungs. Overall, the combined use of simulations and image analysis of in vivo experiments further supports the use of phage therapy for treating acute lung infections caused by P. aeruginosa, while highlighting potential limits to therapy in a spatially structured environment given impaired innate immune responses and/or inefficient phage-induced lysis.

IMPORTANCE

Phage therapy is increasingly employed as a compassionate treatment for severe infections caused by multidrug-resistant (MDR) bacteria. However, the mixed outcomes observed in larger clinical studies highlight a gap in understanding when phage therapy succeeds or fails. Previous research from our team, using in vivo experiments and single-compartment mathematical models, demonstrated the synergistic clearance of acute P. aeruginosa pneumonia by phage and neutrophils despite the emergence of phage-resistant bacteria. In fact, the lung environment is highly structured, prompting the question of whether immunophage synergy explains the curative treatment of P. aeruginosa when incorporating realistic physical connectivity. To address this, we developed a metapopulation network model mimicking the lung branching structure to assess phage therapy efficacy for MDR P. aeruginosa pneumonia. The model predicts the synergistic elimination of P. aeruginosa by phage and neutrophils but emphasizes potential challenges in spatially structured environments, suggesting that higher innate immune levels may be required for successful bacterial clearance. Model simulations reveal a spatial pattern in pathogen clearance where P. aeruginosa are cleared faster at distal nodes of the bronchial tree than in primary nodes. Interestingly, image analysis of infected mice reveals a concordant and statistically significant pattern: infection intensity clears in the bottom before the top of the lungs. The combined use of modeling and image analysis supports the application of phage therapy for acute P. aeruginosa pneumonia while emphasizing potential challenges to curative success in spatially structured in vivo environments, including impaired innate immune responses and reduced phage efficacy.

Multi-strain phage induced clearance of bacterial infections

Bacteriophage (or 'phage' - viruses that infect and kill bacteria) are increasingly considered as a therapeutic alternative to treat antibiotic-resistant bacterial infections. However, bacteria can evolve resistance to phage, presenting a significant challenge to the near- and long-term success of phage therapeutics. Application of mixtures of multiple phage (i.e., 'cocktails') have been proposed to limit the emergence of phage-resistant bacterial mutants that could lead to therapeutic failure. Here, we combine theory and computational models of in vivo phage therapy to study the efficacy of a phage cocktail, composed of two complementary phages motivated by the example of Pseudomonas aeruginosa facing two phages that exploit different surface receptors, LUZ19v and PAK_P1. As confirmed in a Luria-Delbrück fluctuation test, this motivating example serves as a model for instances where bacteria are extremely unlikely to develop simultaneous resistance mutations against both phages. We then quantify therapeutic outcomes given single- or double-phage treatment models, as a function of phage traits and host immune strength. Building upon prior work showing monophage therapy efficacy in immunocompetent hosts, here we show that phage cocktails comprised of phage targeting independent bacterial receptors can improve treatment outcome in immunocompromised hosts and reduce the chance that pathogens simultaneously evolve resistance against phage combinations. The finding of phage cocktail efficacy is qualitatively robust to differences in virus-bacteria interactions and host immune dynamics. Altogether, the combined use of theory and computational analysis highlights the influence of viral life history traits and receptor complementarity when designing and deploying phage cocktails in immunocompetent and immunocompromised hosts.

Bacteriophages isolated from mouse feces attenuates pneumonia mice caused by Pseudomonas aeruginosa

BACKGROUND

Most of the current bacteriophages (phages) are mostly isolated from environments. However, phages isolated from feces might be more specific to the bacteria that are harmful to the host. Meanwhile, some phages from the environment might affect non-pathogenic bacteria for the host.

METHODS

Here, bacteriophages isolated from mouse feces were intratracheally (IT) or intravenously (IV) administered in pneumonia mice caused by Pseudomonas aeruginosa at 2 hours post-intratracheal bacterial administration. As such, the mice with phage treatment, using either IT or IV administration, demonstrated less severe pneumonia as indicated by mortality, serum cytokines, bacteremia, bacterial abundance in bronchoalveolar lavage fluid (BALF), and neutrophil extracellular traps (NETs) in lung tissue (immunofluorescence of neutrophil elastase and myeloperoxidase).

RESULTS

Interestingly, the abundance of phages in BALF from the IT and IV injections was similar, supporting a flexible route of phage administration. With the incubation of bacteria with neutrophils, the presence of bacteriophages significantly improved bactericidal activity, but not NETs formation, with the elevated supernatant IL-6 and TNF-α, but not IL-1β. In conclusion, our findings suggest that bacteriophages against Pseudomonas aeruginosa can be discovered from feces of the host.

CONCLUSIONS

The phages attenuate pneumonia partly through an enhanced neutrophil bactericidal activity, but not via inducing NETs formation. The isolation of phages from the infected hosts themselves might be practically useful for future treatment. More studies are warranted.

Pseudomonas aeruginosa Bacteriophages and Their Clinical Applications

Antimicrobial resistance poses a serious risk to contemporary healthcare since it reduces the number of bacterial illnesses that may be treated with antibiotics, particularly for patients with long-term conditions like cystic fibrosis (CF). People with a genetic predisposition to CF often have recurrent bacterial infections in their lungs due to a buildup of sticky mucus, necessitating long-term antibiotic treatment. Pseudomonas aeruginosa infections are a major cause of CF lung illness, and P. aeruginosa airway isolates are frequently resistant to many antibiotics. Bacteriophages (also known as phages), viruses that infect bacteria, are a viable substitute for antimicrobials to treat P. aeruginosa infections in individuals with CF. Here, we reviewed the utilization of P. aeruginosa bacteriophages both in vivo and in vitro, as well as in the treatment of illnesses and diseases, and the outcomes of the latter.

Macrophage-induced reduction of bacteriophage density limits the efficacy of in vivo pulmonary phage therapy

The rise of antimicrobial resistance has led to renewed interest in evaluating phage therapy. In murine models highly effective treatment of acute pneumonia caused by Pseudomonas aeruginosa relies on the synergistic antibacterial activity of bacteriophages with neutrophils. Here, we show that depletion of alveolar macrophages (AM) shortens the survival of mice without boosting the P. aeruginosa load in the lungs. Unexpectedly, upon bacteriophage treatment, pulmonary levels of P. aeruginosa were significantly lower in AM-depleted than in immunocompetent mice. To explore potential mechanisms underlying the benefit of AM-depletion in treated mice, we developed a mathematical model of phage, bacteria, and innate immune system dynamics. Simulations from the model fitted to data suggest that AM reduce bacteriophage density in the lungs. We experimentally confirmed that the in vivo decay of bacteriophage is faster in immunocompetent compared to AM-depleted animals. These findings demonstrate the involvement of feedback between bacteriophage, bacteria, and the immune system in shaping the outcomes of phage therapy in clinical settings.

Exploring the Impact of Airway Microbiome on Asthma Morbidity: A Focus on the "Constructing a 'Eubiosis Reinstatement Therapy' for Asthma-CURE" Project

The asthma pandemic imposes a huge burden on patients and health systems in both developed and developing countries. Despite available treatments, symptom control is generally suboptimal, and hospitalizations and deaths remain at unacceptably high levels. A pivotal aspect of asthma that warrants further exploration is the influence of the respiratory microbiome and virome in modulating disease activity. A plethora of studies report that the respiratory microbiome is characteristically dysbiotic in asthma. In addition, our data suggest that dysbiosis is also observed on the respiratory virome, partly characterized by the reduced abundance of bacteriophages (phages). Even though phages can naturally infect and control their bacterial prey, phage therapy has been grossly neglected in the Western world, although more recently it is more widely used as a novel tool against bacterial infections. However, it has never been used for tackling microbiome dysbiosis in human non-communicable diseases. This review provides an up-to-date understanding of the microbiome and virome's role within the airways in relation to asthma morbidity. It also advances the rationale and hypothesis for the CURE project. Specifically, the CURE project suggests that managing the respiratory microbiome through phage therapy is viable and may result in restoring eubiosis within the asthmatic airway. This entails controlling immune dysregulation and the clinical manifestation of the disease. To accomplish this goal, it is crucial to predict the effects of introducing specific phage mixtures into the intricate ecology of the airways and devise suitable interventions.

Phage-inspired strategies to combat antibacterial resistance

Antimicrobial resistance (AMR) in clinically priority pathogensis now a major threat to public health worldwide. Phages are bacterial parasites that efficiently infect or kill specific strains and represent the most abundant biological entities on earth, showing great attraction as potential antibacterial therapeutics in combating AMR. This review provides a summary of phage-inspired strategies to combat AMR. We firstly cover the phage diversity, and then explain the biological principles of phage therapy that support the use of phages in the post-antimicrobial era. Furthermore, we state the versatility methods of phage therapy both from direct access as well as collateral access. Among the direct access approaches, we discuss the use of phage cocktail therapy, phage-encoded endolysins and the bioengineering for function improvement of used phages or endolysins. On the other hand, we introduce the collateral access, including the phages antimicrobial immunity combined therapy and phage-based novel antibacterial mimic molecules. Nowadays, more and more talented and enthusiastic scientist, doctors, pharmacists, media, authorities, and industry are promoting the progress of phage therapy, and proposed more phages-inspired strategy to make them more tractable to combat AMR and benefit more people, more animal and diverse environment in "one health" framework.

Metapopulation model of phage therapy of an acute Pseudomonas aeruginosa lung infection

Infections caused by multi-drug resistant (MDR) pathogenic bacteria are a global health threat. Phage therapy, which uses phage to kill bacterial pathogens, is increasingly used to treat patients infected by MDR bacteria. However, the therapeutic outcome of phage therapy may be limited by the emergence of phage resistance during treatment and/or by physical constraints that impede phage-bacteria interactions in vivo. In this work, we evaluate the role of lung spatial structure on the efficacy of phage therapy for Pseudomonas aeruginosa infection. To do so, we developed a spatially structured metapopulation network model based on the geometry of the bronchial tree, and included the emergence of phage-resistant bacterial mutants and host innate immune responses. We model the ecological interactions between bacteria, phage, and the host innate immune system at the airway (node) level. The model predicts the synergistic elimination of a P. aeruginosa infection due to the combined effects of phage and neutrophils given sufficiently active immune states and suitable phage life history traits. Moreover, the metapopulation model simulations predict that local MDR pathogens are cleared faster at distal nodes of the bronchial tree. Notably, image analysis of lung tissue time series from wild-type and lymphocyte-depleted mice (n=13) revealed a concordant, statistically significant pattern: infection intensity cleared in the bottom before the top of the lungs. Overall, the combined use of simulations and image analysis of in vivo experiments further supports the use of phage therapy for treating acute lung infections caused by P. aeruginosa while highlighting potential limits to therapy given a spatially structured environment, such as impaired innate immune responses and low phage efficacy.

Genomic analysis of vB_PaS-HSN4 bacteriophage and its antibacterial activity (in vivo and in vitro) against Pseudomonas aeruginosa isolated from burn

The most frequent infections caused by Pseudomonas aeruginosa are local infections in soft tissues, including burns. Today, phage use is considered a suitable alternative to cure infections caused by multi-drug-resistant (MDR) and extensively drug-resistant (XDR) bacteria. We investigated the potential of a novel phage (vB_PaS-HSN4) belonging to Caudoviricetes class, against XDR and MDR P. aeruginosa strains in vivo and in vitro. Its biological and genetic characteristics were investigated. The phage burst size and latent were 119 and 20 min, respectively. It could tolerate a broad range of salt concentrations, pH values, and temperatures. The combination with ciprofloxacin significantly enhanced biofilm removal after 24 h. The genome was dsDNA with a size of 44,534 bp and encoded 61 ORFs with 3 tRNA and 5 promoters. No virulence factor was observed in the phage genome. In the in vivo infection model, treatment with vB_PaS-HSN4 increased Galleria mellonella larvae survival (80%, 66%, and 60%) (MOI 100) and (60%, 40%, and 26%) (MOI 1) in the pre-treatment, co-treatment, and post-treatment experiments, respectively. Based on these characteristics, it can be considered for the cure of infections of burns caused by P. aeruginosa.

Phage-host-immune system dynamics in bacteriophage therapy: basic principles and mathematical models

Phage therapy is progressively being recognized as a viable alternative to conventional antibiotic treatments, particularly in the context of multi-drug resistant bacterial challenges. However, the intricacies of the pharmacokinetics and pharmacodynamics (PKPD) pertaining to phages remain inadequately elucidated. A salient characteristic of phage PKPD is the inherent ability of phages to undergo replication. In this review, I proffer mathematical models that delineate the intricate dynamics encompassing the phage, the host organism, and the immune system. Fundamental tenets associated with proliferative and inundation thresholds are explored, and distinctions between active and passive therapies are accentuated. Furthermore, I present models that aim to illuminate the multifaceted interactions amongst diverse phage strains and bacterial subpopulations, each possessing distinct sensitivities to phages. The synergistic relationship between phages and the immune system is critically examined, demonstrating how the host's immunological function can influence the requisite phage dose for an optimal therapeutic outcome. A profound understanding of the presented modeling methodologies is paramount for researchers in the realms of clinical pharmacology and PKPD modeling interested in phage therapy. Such insights facilitate a more nuanced interpretation of dose-response relationships, enable the selection of potent phages, and aid in the optimization of phage cocktails.

Effective treatment of a broad-host-range lytic phage SapYZU15 in eliminating Staphylococcus aureus from subcutaneous infection

Multidrug resistance (MDR) Staphylococcus aureus is frequently isolated from food products, and can cause severe clinical infection. Bacteriophage (phage) therapy is a promising biocontrol agent against MDR S. aureus in food contamination and clinical infections. In this study, the antimicrobial susceptibility of 47 S. aureus isolates from three swine farms, two slaughterhouses, and four markets (Yangzhou, China) were evaluated. The biological characteristics of four lytic S. aureus phages were compared and the lytic activity of phage SapYZU15 against MDR S. aureus was assessed using milk, fresh pork and a mouse model of subcutaneous abscess. The results showed that 28 S. aureus isolates (59.6%, 28/47) exhibited multiple antibiotic resistance to at least three different classes of antibiotics. Compared to SapYZU01, SapYZU02, and SapYZU03, SapYZU15 had a shorter latent period (10 min), larger burst size (322.00 PFU/cell), broader host range, wider temperature stability (-80 to 50 °C), and pH stability. Furthermore, SapYZU15 significantly reduces the counts of S. aureus in milk and pork (5.69 and 1.16 log colony-forming unit/mL, respectively) at 25 °C and controls the growth of S. aureus at 4 °C. Compared to the mice infected with S. aureus MRSA JCSC 4744 and cocktail (S. aureus YZUsa1, YZUsa4, YZUsa12, YZUsa14, and MRSA JCSC 4744), treatment with SapYZU15 led to faster tissue healing, less weight loss, and lower viable S. aureus counts in the murine abscess model. Moreover, prevention with SapYZU15 effectively inhibited abscess formation through a synergistic effect with pro-inflammatory cytokines. Consequently, our results suggest that SapYZU15 is an effective strategy for controlling S. aureus contamination in food products, and possesses an immense potential to treat and prevent clinic infection caused by MDR S. aureus strains. The interactions and mechanisms between SapYZU15 and its bacterial host differed depending on the model, temperature, and multiplicity of infection (MOI).

Automating Predictive Phage Therapy Pharmacology

Viruses that infect as well as often kill bacteria are called bacteriophages, or phages. Because of their ability to act bactericidally, phages increasingly are being employed clinically as antibacterial agents, an infection-fighting strategy that has been in practice now for over one hundred years. As with antibacterial agents generally, the development as well as practice of this phage therapy can be aided via the application of various quantitative frameworks. Therefore, reviewed here are considerations of phage multiplicity of infection, bacterial likelihood of becoming adsorbed as a function of phage titers, bacterial susceptibility to phages also as a function of phage titers, and the use of Poisson distributions to predict phage impacts on bacteria. Considered in addition is the use of simulations that can take into account both phage and bacterial replication. These various approaches can be automated, i.e., by employing a number of online-available apps provided by the author, the use of which this review emphasizes. In short, the practice of phage therapy can be aided by various mathematical approaches whose implementation can be eased via online automation.

Improving the safety and efficacy of phage therapy from the perspective of phage-mammal interactions

Phage therapy has re-emerged as a promising solution for combating antimicrobial-resistant bacterial infections. Increasingly, studies have revealed that phages possess therapeutic potential beyond their antimicrobial properties, including regulating the gut microbiome and maintain intestinal homeostasis, as a novel nanocarrier for targeted drug delivery. However, the complexity and unpredictability of phage behavior during treatment pose a significant challenge in clinical practice. The intricate interactions established between phages, humans, and bacteria throughout their long coexistence in the natural ecosystem contribute to the complexity of phage behavior in therapy, raising concerns about their efficacy and safety as therapeutic agents. Revealing the mechanisms by which phages interact with the human body will provide a theoretical basis for increased application of promising phage therapy. In this review, we provide a comprehensive summary of phage-mammal interactions, including signaling pathways, adaptive immunity responses, and phage-mediated anti-inflammatory responses. Then, from the perspective of phage-mammalian immune system interactions, we present the first systematic overview of the factors affecting phage therapy, such as the mode of administration, the physiological status of the patient, and the biological properties of the phage, to offer new insights into phage therapy for various human diseases.

Acinetobacter Baumannii Phages: Past, Present and Future

Acinetobacter baumannii (A. baumannii) is one of the most common clinical pathogens and a typical multi-drug resistant (MDR) bacterium. With the increase of drug-resistant A. baumannii infections, it is urgent to find some new treatment strategies, such as phage therapy. In this paper, we described the different drug resistances of A. baumannii and some basic properties of A. baumannii phages, analyzed the interaction between phages and their hosts, and focused on A. baumannii phage therapies. Finally, we discussed the chance and challenge of phage therapy. This paper aims to provide a more comprehensive understanding of A. baumannii phages and theoretical support for the clinical application of A. baumannii phages.

The role of the animal host in the management of bacteriophage resistance during phage therapy

Multi-drug-resistant bacteria are associated with significantly higher morbidity and mortality. The possibilities for discovering new antibiotics are limited, but phage therapy - the use of bacteriophages (viruses infecting bacteria) to cure infections - is now being investigated as an alternative or complementary treatment to antibiotics. However, one of the major limitations of this approach lies in the antagonistic coevolution between bacteria and bacteriophages, which determines the ultimate success or failure of phage therapy. Here, we review the possible influence of the animal host on phage resistance and its consequences for the efficacy of phage therapy. We also discuss the value of in vitro assays for anticipating the dynamics of phage resistance observed in vivo.

The dynamic interplay of bacteriophage, bacteria and the mammalian host during phage therapy

For decades, biomedically centered studies of bacteria have focused on mechanistic drivers of disease in their mammalian hosts. Likewise, molecular studies of bacteriophage have centered on understanding mechanisms by which bacteriophage exploit the intracellular environment of their bacterial hosts. These binary interactions - bacteriophage infect bacteria and bacteria infect eukaryotic hosts - have remained largely separate lines of inquiry. However, recent evidence demonstrates how tripartite interactions between bacteriophage, bacteria and the eukaryotic host shape the dynamics and fate of each component. In this perspective, we provide an overview of different ways in which bacteriophage ecology modulates bacterial infections along a spectrum of positive to negative impacts on a mammalian host. We also examine how coevolutionary processes over longer timescales may change the valence of these interactions. We argue that anticipating both ecological and evolutionary dynamics is key to understand and control tripartite interactions and ultimately to the success or failure of phage therapy.

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.

Fecal Microbiota Transplantation and Other Gut Microbiota Manipulation Strategies

The gut microbiota is composed of bacteria, archaea, phages, and protozoa. It is now well known that their mutual interactions and metabolism influence host organism pathophysiology. Over the years, there has been growing interest in the composition of the gut microbiota and intervention strategies in order to modulate it. Characterizing the gut microbial populations represents the first step to clarifying the impact on the health/illness equilibrium, and then developing potential tools suited for each clinical disorder. In this review, we discuss the current gut microbiota manipulation strategies available and their clinical applications in personalized medicine. Among them, FMT represents the most widely explored therapeutic tools as recent guidelines and standardization protocols, not only for intestinal disorders. On the other hand, the use of prebiotics and probiotics has evidence of encouraging findings on their safety, patient compliance, and inter-individual effectiveness. In recent years, avant-garde approaches have emerged, including engineered bacterial strains, phage therapy, and genome editing (CRISPR-Cas9), which require further investigation through clinical trials.

Cocktail, a Computer Program for Modelling Bacteriophage Infection Kinetics

Cocktail is an easy-to-use computer program for mathematical modelling of bacteriophage (phage) infection kinetics in a chemostat. The infection of bacteria by phages results in complicated dynamic processes as both have the ability to multiply and change during the course of an infection. There is a need for a simple way to visualise these processes, not least due to the increased interest in phage therapy. Cocktail is completely self-contained and runs on a Windows 64-bit operating system. By changing the publicly available source code, the program can be developed in the directions that users see fit. Cocktail's models consist of coupled differential equations that describe the infection of a bacterium in a vessel by one or two (interfering) phages. In the models, the bacterial population can be controlled by sixteen parameters, for example, through different growth rates, phage resistance, metabolically inactive cells or biofilm formation. The phages can be controlled by eight parameters each, such as different adsorption rates or latency periods. As the models in Cocktail describe the infection kinetics of phages in vitro, the program is primarily intended to generate hypotheses, but the results can however be indicative in the application of phage therapy.

Determination of phage load and administration time in simulated occurrences of antibacterial treatments

The use of phages as antibacterials is becoming more and more common in Western countries. However, a successful phage-derived antibacterial treatment needs to account for additional features such as the loss of infective virions and the multiplication of the hosts. The parameters critical inoculation size (V F ) and failure threshold time (T F ) have been introduced to assure that the viral dose (V ϕ) and administration time (T ϕ) would lead to the extinction of the targeted bacteria. The problem with the definition of V F and T F is that they are non-linear equations with two unknowns; thus, obtaining their explicit values is cumbersome and not unique. The current study used machine learning to determine V F and T F for an effective antibacterial treatment. Within these ranges, a Pareto optimal solution of a multi-criterial optimization problem (MCOP) provided a pair of V ϕ and T ϕ to facilitate the user's work. The algorithm was tested on a series of in silico microbial consortia that described the outgrowth of a species at high cell density by another species initially present at low concentration. The results demonstrated that the MCOP-derived pairs of V ϕ and T ϕ could effectively wipe out the bacterial target within the context of the simulation. The present study also introduced the concept of mediated phage therapy, where targeting booster bacteria might decrease the virulence of a pathogen immune to phagial infection and highlighted the importance of microbial competition in attaining a successful antibacterial treatment. In summary, the present work developed a novel method for investigating phage/bacteria interactions that can help increase the effectiveness of the application of phages as antibacterials and ease the work of microbiologists.

Phage Therapy: A Different Approach to Fight Bacterial Infections

Phage therapy is one of the alternatives to treat infections caused by both antibiotic-sensitive and antibiotic-resistant bacteria, with no or low toxicity to patients. It was started a century ago, although rapidly growing bacterial antimicrobial resistance, resulting in high levels of morbidity, mortality, and financial cost, has initiated the revival of phage therapy. It involves the use of live lytic, bioengineered, phage-encoded biological products, in combination with chemical antibiotics to treat bacterial infections. Importantly, phages will be removed from the body within seven days of clearing an infection. They target specific bacterial strains and cause minimal disruption to the microbial balance in humans. Phages for medication must be screened for the absence of resistant genes, virulent genes, cytotoxicity, and their interaction with the host tissue and organs. Since they are immunogenic, applying a high phage titer for therapy exposes them and activates the host immune system. To date, no serious side effects have been reported with human phage therapy. In this review, we describe phage–phagocyte interaction, bacterial resistance to phages, how phages conquer bacterial resistance, the role of genetic engineering and other technologies in phage therapy, and the therapeutic application of modified phages and phage-encoded products. We also highlight the comparison of antibiotics and lytic phage therapy, the pros and cons of phage therapy, determinants of human phage therapy trials, phage quality and safety requirements, phage storage and handling, and current challenges in phage therapy.

Phenotypic flux: The role of physiology in explaining the conundrum of bacterial persistence amid phage attack

Bacteriophages, the viruses of bacteria, have been studied for over a century. They were not only instrumental in laying the foundations of molecular biology, but they are also likely to play crucial roles in shaping our biosphere and may offer a solution to the control of drug-resistant bacterial infections. However, it remains challenging to predict the conditions for bacterial eradication by phage predation, sometimes even under well-defined laboratory conditions, and, most curiously, if the majority of surviving cells are genetically phage-susceptible. Here, I propose that even clonal phage and bacterial populations are generally in a state of continuous 'phenotypic flux', which is caused by transient and nongenetic variation in phage and bacterial physiology. Phenotypic flux can shape phage infection dynamics by reducing the force of infection to an extent that allows for coexistence between phages and susceptible bacteria. Understanding the mechanisms and impact of phenotypic flux may be key to providing a complete picture of phage-bacteria coexistence. I review the empirical evidence for phenotypic variation in phage and bacterial physiology together with the ways they have been modeled and discuss the potential implications of phenotypic flux for ecological and evolutionary dynamics between phages and bacteria, as well as for phage therapy.

The immunomodulatory potential of phage therapy to treat acne: a review on bacterial lysis and immunomodulation

Background

Characterized by an inflammatory pathogenesis, acne is the most common skin disorder worldwide. Altered sebum production, abnormal proliferation of keratinocytes, and microbiota dysbiosis represented by disbalance in Cutibacterium acnes population structure, have a synergic effect on inflammation of acne-compromised skin. Although the role of C. acnes as a single factor in acne development is still under debate, it is known that skin and skin-resident immune cells recognize this bacterium and produce inflammatory markers as a result. Control of the inflammatory response is frequently the target for acne treatment, using diverse chemical or physical agents including antibiotics. However, some of these treatments have side effects that compromise patient adherence and drug safety and in the case of antibiotics, it has been reported C. acnes resistance to these molecules. Phage therapy is an alternative to treat antibiotic-resistant bacterial strains and have been recently proposed as an immunomodulatory therapy. Here, we explore this perspective about phage therapy for acne, considering the potential immunomodulatory role of phages.

Methodology

Literature review was performed using four different databases (Europe PubMed Central-ePMC, Google Scholar, PubMed, and ScienceDirect). Articles were ordered and selected according to their year of publication, number of citations, and quartile of the publishing journal.

Results

The use of lytic bacteriophages to control bacterial infections has proven its promising results, and anti-inflammatory effects have been found for some bacteriophages and phage therapy. These effects can be related to bacterial elimination or direct interaction with immune cells that result in the regulation of pro-inflammatory cytokines. Studies on C. acnes bacteriophages have investigated their lytic activity, genomic structure, and stability on different matrices. However, studies exploring the potential of immunomodulation of these bacteriophages are still scarce.

Conclusions

C. acnes bacteriophages, as well as other phages, may have direct immunomodulatory effects that are yet to be fully elucidated. To our knowledge, to the date that this review was written, there are only two studies that investigate anti-inflammatory properties for C. acnes bacteriophages. In those studies, it has been evidenced reduction of pro-inflammatory response to C. acnes inoculation in mice after bacteriophage application. Nevertheless, these studies were conducted in mice, and the interaction with the immune response was not described. Phage therapy to treat acne can be a suitable therapeutic alternative to C. acnes control, which in turn can aid to restore the skin's balance of microbiota. By controlling C. acnes colonization, C. acnes bacteriophages can reduce inflammatory reactions triggered by this bacterium.

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.

Combination of in vivo phage therapy data with in silico model highlights key parameters for pneumonia treatment efficacy

The clinical (re)development of bacteriophage (phage) therapy to treat antibiotic-resistant infections faces the challenge of understanding the dynamics of phage-bacteria interactions in the in vivo context. Here, we develop a general strategy coupling in vitro and in vivo experiments with a mathematical model to characterize the interplay between phage and bacteria during pneumonia induced by a pathogenic strain of Escherichia coli. The model allows the estimation of several key parameters for phage therapeutic efficacy. In particular, it quantifies the impact of dose and route of phage administration as well as the synergism of phage and the innate immune response on bacterial clearance. Simulations predict a limited impact of the intrinsic phage characteristics in agreement with the current semi-empirical choices of phages for compassionate treatments. Model-based approaches will foster the deployment of future phage-therapy clinical trials.

The Bacteriophage vB_CbrM_HP1 Protects Crucian Carp Against Citrobacter braakii Infection

Citrobacter braakii is an opportunistic pathogen that induces aquatic infections in fish and turtles. In this study, a bacteriophage that infects C. braakii, named vB_CbrM_HP1, was isolated from sewage. This phage belongs to Myoviridae family, Ounavirinae subfamily, Mooglevirus genus. We also used the phage to treat crucian carp infection caused by C. braakii for the first time. vB_CbrM_HP1 was relatively stable at temperatures ranging from 4 to 60°C and pH values ranging from 3 to 11 but float slightly. When the multiplicities of infection (MOI) was 0.0001, the titer reached a maximum of 4.20 × 1010 PFU/ml. As revealed from the results of whole genomic sequence analysis, the total length of vB_CbrM_HP1 was 89335 bp, encoding 135 ORFs, 9 of which were &lt;75% similar to the known sequences in NCBI. The phage vB_CbrM_HP1 showed a highly efficient bactericidal effect against C. braakii both in vitro and in vivo. In vitro, vB_CbrM_HP1 was capable of effectively killing bacteria (the colony count decreased by 4.7 log units at 5 h). In vivo, administration of vB_CbrM_HP1 (1 × 109 PFU) effectively protected crucian carp against fatal infection caused by C. braakii. Phage treatment reduced the levels of inflammatory factors. All these results demonstrated the potential of vB_CbrM_HP1 as an alternative treatment strategy for infections caused by C. braakii.

Parallel evolution of Pseudomonas aeruginosa phage resistance and virulence loss in response to phage treatment in vivo and in vitro

With rising antibiotic resistance, there has been increasing interest in treating pathogenic bacteria with bacteriophages (phage therapy). One limitation of phage therapy is the ease at which bacteria can evolve resistance. Negative effects of resistance may be mitigated when resistance results in reduced bacterial growth and virulence, or when phage coevolves to overcome resistance. Resistance evolution and its consequences are contingent on the bacteria-phage combination and their environmental context, making therapeutic outcomes hard to predict. One solution might be to conduct ‘in vitro evolutionary simulations’ using bacteria-phage combinations from the therapeutic context. Overall, our aim was to investigate parallels between in vitro experiments and in vivo dynamics in a human participant. Evolutionary dynamics were similar, with high levels of resistance evolving quickly with limited evidence of phage evolution. Resistant bacteria—evolved in vitro and in vivo—had lower virulence. In vivo, this was linked to lower growth rates of resistant isolates, whereas in vitro phage resistant isolates evolved greater biofilm production. Population sequencing suggests resistance resulted from selection on de novo mutations rather than sorting of existing variants. These results highlight the speed at which phage resistance can evolve in vivo, and how in vitro experiments may give useful insights for clinical evolutionary outcomes.

A Review of Using Mathematical Modeling to Improve Our Understanding of Bacteriophage, Bacteria, and Eukaryotic Interactions

Phage therapy, the therapeutic usage of viruses to treat bacterial infections, has many theoretical benefits in the ‘post antibiotic era.’ Nevertheless, there are currently no approved mainstream phage therapies. One reason for this is a lack of understanding of the complex interactions between bacteriophage, bacteria and eukaryotic hosts. These three-component interactions are complex, with non-linear or synergistic relationships, anatomical barriers and genetic or phenotypic heterogeneity all leading to disparity between performance and efficacy in in vivo versus in vitro environments. Realistic computer or mathematical models of these complex environments are a potential route to improve the predictive power of in vitro studies for the in vivo environment, and to streamline lab work. Here, we introduce and review the current status of mathematical modeling and highlight that data on genetic heterogeneity and mutational stochasticity, time delays and population densities could be critical in the development of realistic phage therapy models in the future. With this in mind, we aim to inform and encourage the collaboration and sharing of knowledge and expertise between microbiologists and theoretical modelers, synergising skills and smoothing the road to regulatory approval and widespread use of phage therapy.

Antiviral effect of a bacteriophage on murine norovirus replication via modulation of the innate immune response

Bacteriophages (phages) are viruses of bacteria. Despite the growing progress in research on phage interactions with eukaryotic cells, our understanding of the roles of phages and their potential implications remains incomplete. The objective of this study was to investigate the effects of the Staphylococcus aureus phage vB_SauM_JS25 on murine norovirus (MNV) replication. Experiments were performed using the RAW 264.7 cell line. After phage treatment, MNV multiplication was significantly inhibited, as indicated by real-time quantitative polymerase chain reaction (RT-qPCR) analysis, western blotting, the 50% tissue culture infectious dose and immunofluorescence. Furthermore, we revealed transcriptional changes in phage/MNV co-incubated RAW 264.7 cells through RNA sequencing (RNA-seq) and bioinformatic analysis. Our subsequent analyses revealed that the innate immune response might play an important role in restriction of MNV replication, such as the cellular response to IFN-γ and response to IFN-γ. Additionally, gene expression of IL-10, Arg-1, Ccl22, GBP2, GBP3, GBP5, and GBP7 was increased significantly, which indicated a strong correlation between RT-qPCR and RNA-seq results. Furthermore, phage treatment activated guanylate binding proteins (GBPs), as revealed by RT-qPCR analysis, western blotting, and confocal microscopy. Taken together, these data suggest that the phage affects the innate response, such as the IFN-inducible GTPases and GBPs, and therefore exerts an antiviral effect in vitro. Collectively, our findings provide insights into the interactions of immune cells and phages, which establish phage-based antiviral effects.

The Safety and Toxicity of Phage Therapy: A Review of Animal and Clinical Studies

Increasing rates of infection by antibiotic resistant bacteria have led to a resurgence of interest in bacteriophage (phage) therapy. Several phage therapy studies in animals and humans have been completed over the last two decades. We conducted a systematic review of safety and toxicity data associated with phage therapy in both animals and humans reported in English language publications from 2008-2021. Overall, 69 publications met our eligibility criteria including 20 animal studies, 35 clinical case reports or case series, and 14 clinical trials. After summarizing safety and toxicity data from these publications, we discuss potential approaches to optimize safety and toxicity monitoring with the therapeutic use of phage moving forward. In our systematic review of the literature, we found some adverse events associated with phage therapy, but serious events were extremely rare. Comprehensive and standardized reporting of potential toxicities associated with phage therapy has generally been lacking in the published literature. Structured safety and tolerability endpoints are necessary when phages are administered as anti-infective therapeutics.

Stability analysis and persistence of a phage therapy model

This study deals with a phage therapy model involving nonlinear interactions of the bacteria-phage-innate immune response. The main aim of this work is to analytically and numerically examine the dynamic behavior of the phage therapy model. First, we investigate the positivity and boundedness of the system. Second, we analyze the existence and local asymptotic stability of different equilibrium solutions. Third, we investigate the global stability for equilibrium without immune system and equilibrium without phages, and coexistence equilibrium by means of the Bendixson-Dulac criterion and the Lyapunov functional method, respectively. Furthermore, we discuss the persistence and nonpersistence of the system under some conditions. Finally, we perform numerical simulations to substantiate the results obtained in this research.

Rekindling of a Masterful Precedent; Bacteriophage: Reappraisal and Future Pursuits

Antibiotic resistance is exuberantly becoming a deleterious health problem world-wide. Seeking innovative approaches is necessary in order to circumvent such a hazard. An unconventional fill-in to antibiotics is bacteriophage. Bacteriophages are viruses capable of pervading bacterial cells and disrupting their natural activity, ultimately resulting in their defeat. In this article, we will run-through the historical record of bacteriophage and its correlation with bacteria. We will also delineate the potential of bacteriophage as a therapeutic antibacterial agent, its supremacy over antibiotics in multiple aspects and the challenges that could arise on the way to its utilization in reality. Pharmacodynamics, pharmacokinetics and genetic engineering of bacteriophages and its proteins will be briefly discussed as well. In addition, we will highlight some of the in-use applications of bacteriophages, and set an outlook for their future ones. We will also overview some of the miscellaneous abilities of these tiny viruses in several fields other than the clinical one. This is an attempt to encourage tackling a long-forgotten hive. Perhaps, one day, the smallest of the creatures would be of the greatest help.

Pre-optimized phage therapy on secondary Acinetobacter baumannii infection in four critical COVID-19 patients

Phage therapy is recognized as a promising alternative to antibiotics in treating pulmonary bacterial infections, however, its use has not been reported for treating secondary bacterial infections during virus pandemics such as coronavirus disease 2019 (COVID-19). We enrolled 4 patients hospitalized with critical COVID-19 and pulmonary carbapenem-resistant Acinetobacter baumannii (CRAB) infections to compassionate phage therapy (at 2 successive doses of 10⁹ plaque-forming unit phages). All patients in our COVID-19-specific intensive care unit (ICU) with CRAB positive in bronchoalveolar lavage fluid or sputum samples were eligible for study inclusion if antibiotic treatment failed to eradicate their CRAB infections. While phage susceptibility testing revealed an identical profile of CRAB strains from these patients, treatment with a pre-optimized 2-phage cocktail was associated with reduced CRAB burdens. Our results suggest the potential of phages on rapid responses to secondary CRAB outbreak in COVID-19 patients.

Reapproaching Old Treatments: Considerations for PK/PD Studies on Phage Therapy for Bacterial Respiratory Infections

Antibiotic resistant bacterial respiratory infections are a significant global health burden, and new therapeutic strategies are needed to control the problem. For bacterial respiratory infections, this need is emphasized by the rise in antibiotic resistance and a lean drug development pipeline. Bacteriophage (phage) therapy is a promising alternative to antibiotics. Phage are viruses that infect and kill bacteria. Because phage and antibiotics differ in their bactericidal mechanisms, phage are a treatment option for antibiotic-resistant bacteria. Here, we review the history of phage therapy and highlight recent preclinical and clinical case reports of its use for treating antibiotic-resistant respiratory infections. The ability of phage to replicate while killing the bacteria is both a benefit for treatment and a challenge for pharmacokinetic (PK) and pharmacodynamic (PD) studies. In this review, we will discuss how the phage lifecycle and associated bidirectional interactions between phage and bacteria can impact treatment. We will also highlight PK/PD considerations for designing studies of phage therapy to optimize the efficacy and feasibility of the approach.

Characterization of a Novel Bacteriophage Henu2 and Evaluation of the Synergistic Antibacterial Activity of Phage-Antibiotics

Staphylococcus aureus phage Henu2 was isolated from a sewage sample collected in Kaifeng, China, in 2017. In this study, Henu2, a linear double-stranded DNA virus, was sequenced and found to be 43,513 bp long with 35% G + C content and 63 putative open reading frames (ORFs). Phage Henu2 belongs to the family Siphoviridae and possesses an isometric head (63 nm in diameter). The latent time and burst size of Henu2 were approximately 20 min and 7.8 plaque forming unit (PFU)/infected cells. The Henu2 maintained infectivity over a wide range of temperature (10–60 °C) and pH values (4–12). Phylogenetic and comparative genomic analyses indicate that Staphylococcus aureus phage Henu2 should be a new member of the family of Siphoviridae class-II. In this paper, Phage Henu2 alone exhibited weak inhibitory activity on the growth of S. aureus. However, the combination of phage Henu2 and some antibiotics or oxides could effectively inhibit the growth of S. aureus, with a decrease of more than three logs within 24 h in vitro. These results provide useful information that phage Henu2 can be combined with antibiotics to increase the production of phage Henu2 and thus enhance the efficacy of bacterial killing.

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.

Fighting microbial pathogens by integrating host ecosystem interactions and evolution

Successful therapies to combat microbial diseases and cancers require incorporating ecological and evolutionary principles. Drawing upon the fields of ecology and evolutionary biology, we present a systems-based approach in which host and disease-causing factors are considered as part of a complex network of interactions, analogous to studies of "classical" ecosystems. Centering this approach around empirical examples of disease treatment, we present evidence that successful therapies invariably engage multiple interactions with other components of the host ecosystem. Many of these factors interact nonlinearly to yield synergistic benefits and curative outcomes. We argue that these synergies and nonlinear feedbacks must be leveraged to improve the study of pathogenesis in situ and to develop more effective therapies. An eco-evolutionary systems perspective has surprising and important consequences, and we use it to articulate areas of high research priority for improving treatment strategies.

Antimycobacterial Potential of Mycobacteriophage Under Disease-Mimicking Conditions

Antibiotic resistance continues to be a major global health risk with an increase in multi-drug resistant infections seen across nearly all bacterial diseases. Mycobacterial infections such as Tuberculosis (TB) and Non-Tuberculosis infections have seen a significant increase in the incidence of multi-drug resistant and extensively drug-resistant infections. With this increase in drug-resistant Mycobacteria, mycobacteriophage therapy offers a promising alternative. However, a comprehensive study on the infection dynamics of mycobacteriophage against their host bacteria and the evolution of bacteriophage (phage) resistance in the bacteria remains elusive. We aim to study the infection dynamics of a phage cocktail against Mycobacteria under various pathophysiological conditions such as low pH, low growth rate and hypoxia. We show that mycobacteriophages are effective against M. smegmatis under various conditions and the phage cocktail prevents emergence of resistance for long durations. Although the phages are able to amplify after infection, the initial multiplicity of infection plays an important role in reducing the bacterial growth and prolonging efficacy. Mycobacteriophages are effective against antibiotic-resistant strains of Mycobacterium and show synergy with antibiotics such as rifampicin and isoniazid. Finally, we also show that mycobacteriophages are efficient against M. tuberculosis both under lag and log phase for several weeks. These findings have important implications for developing phage therapy for Mycobacterium.

Optimal control to reach eco-evolutionary stability in metastatic castrate-resistant prostate cancer

In the absence of curative therapies, treatment of metastatic castrate-resistant prostate cancer (mCRPC) using currently available drugs can be improved by integrating evolutionary principles that govern proliferation of resistant subpopulations into current treatment protocols. Here we develop what is coined as an 'evolutionary stable therapy', within the context of the mathematical model that has been used to inform the first adaptive therapy clinical trial of mCRPC. The objective of this therapy is to maintain a stable polymorphic tumor heterogeneity of sensitive and resistant cells to therapy in order to prolong treatment efficacy and progression free survival. Optimal control analysis shows that an increasing dose titration protocol, a very common clinical dosing process, can achieve tumor stabilization for a wide range of potential initial tumor compositions and volumes. Furthermore, larger tumor volumes may counter intuitively be more likely to be stabilized if sensitive cells dominate the tumor composition at time of initial treatment, suggesting a delay of initial treatment could prove beneficial. While it remains uncertain if metastatic disease in humans has the properties that allow it to be truly stabilized, the benefits of a dose titration protocol warrant additional pre-clinical and clinical investigations.

Synergistic activity of phage PEV20-ciprofloxacin combination powder formulation-A proof-of-principle study in a P. aeruginosa lung infection model

Combination treatment using bacteriophage and antibiotics is potentially an advanced approach to combatting antimicrobial-resistant bacterial infections. We have recently developed an inhalable powder by co-spray drying Pseudomonas phage PEV20 with ciprofloxacin. The purpose of this study was to assess the in vivo effect of the powder using a neutropenic mouse model of acute lung infection. The synergistic activity of PEV20 and ciprofloxacin was investigated by infecting mice with P. aeruginosa, then administering freshly spray-dried single PEV20 (10⁶ PFU/mg), single ciprofloxacin (0.33 mg/mg) or combined PEV20-ciprofloxacin treatment using a dry powder insufflator. Lung tissues were then harvested for colony counting and flow cytometry analysis at 24 h post-treatment. PEV20 and ciprofloxacin combination powder significantly reduced the bacterial load of clinical P. aeruginosa strain in mouse lungs by 5.9 log₁₀ (p < 0.005). No obvious reduction in the bacterial load was observed when the animals were treated only with PEV20 or ciprofloxacin. Assessment of immunological responses in the lungs showed reduced inflammation associating with the bactericidal effect of the PEV20-ciprofloxacin powder. In conclusion, this study has demonstrated the synergistic potential of using the combination PEV20-ciprofloxacin powder for P. aeruginosa respiratory infections.

Genomic, Morphological and Functional Characterization of Virulent Bacteriophage IME-JL8 Targeting Citrobacter freundii

Citrobacter freundii refers to a fish pathogen extensively reported to be able to cause injury and high mortality. Phage therapy is considered a process to alternatively control bacterial infections and contaminations. In the present study, the isolation of a virulent bacteriophage IME-JL8 isolated from sewage was presented, and such bacteriophage was characterized to be able to infect Citrobacter freundii specifically. Phage IME-JL8 has been classified as the member of the Siphoviridae family, which exhibits the latent period of 30–40 min. The pH and thermal stability of phage IME-JL8 demonstrated that this bacteriophage achieved a pH range of 4–10 as well as a temperature range of 4, 25, and 37°C. As revealed from the results of whole genomic sequence analysis, IME-JL8 covers a double-stranded genome of 49,838 bp (exhibiting 47.96% G+C content), with 80 putative coding sequences contained. No bacterial virulence- or lysogenesis-related ORF was identified in the IME-JL8 genome, so it could be applicable to phage therapy. As indicated by the in vitro experiments, phage IME-JL8 is capable of effectively removing bacteria (the colony count decreased by 6.8 log units at 20 min), and biofilm can be formed in 24 h. According to the in vivo experiments, administrating IME-JL8 (1 × 10⁷ PFU) was demonstrated to effectively protect the fish exhibiting a double median lethal dose (2 × 10⁹ CFU/carp). Moreover, the phage treatment led to the decline of pro-inflammatory cytokines in carp with lethal infections. IME-JL8 was reported to induce efficient lysis of Citrobacter freundii both in vitro and in vivo, thereby demonstrating its potential as an alternative treatment strategy for infections attributed to Citrobacter freundii.

Kinetic Fingerprinting Links Bacteria-Phage Interactions with Emergent Dynamics: Rapid Depletion of Klebsiella pneumoniae Indicates Phage Synergy

The specific temporal evolution of bacterial and phage population sizes, in particular bacterial depletion and the emergence of a resistant bacterial population, can be seen as a kinetic fingerprint that depends on the manifold interactions of the specific phage-host pair during the course of infection. We have elaborated such a kinetic fingerprint for a human urinary tract Klebsiella pneumoniae isolate and its phage vB_KpnP_Lessing by a modeling approach based on data from in vitro co-culture. We found a faster depletion of the initially sensitive bacterial population than expected from simple mass action kinetics. A possible explanation for the rapid decline of the bacterial population is a synergistic interaction of phages which can be a favorable feature for phage therapies. In addition to this interaction characteristic, analysis of the kinetic fingerprint of this bacteria and phage combination revealed several relevant aspects of their population dynamics: A reduction of the bacterial concentration can be achieved only at high multiplicity of infection whereas bacterial extinction is hardly accomplished. Furthermore the binding affinity of the phage to bacteria is identified as one of the most crucial parameters for the reduction of the bacterial population size. Thus, kinetic fingerprinting can be used to infer phage-host interactions and to explore emergent dynamics which facilitates a rational design of phage therapies.

Phage steering of antibiotic-resistance evolution in the bacterial pathogen, Pseudomonas aeruginosa

Background and objectives

Antimicrobial resistance is a growing global concern and has spurred increasing efforts to find alternative therapeutics. Bacteriophage therapy has seen near constant use in Eastern Europe since its discovery over a century ago. One promising approach is to use phages that not only reduce bacterial pathogen loads but also select for phage resistance mechanisms that trade-off with antibiotic resistance-so called 'phage steering'.

Methodology

Recent work has shown that the phage OMKO1 can interact with efflux pumps and in so doing select for both phage resistance and antibiotic sensitivity of the pathogenic bacterium Pseudomonas aeruginosa. We tested the robustness of this approach to three different antibiotics in vitro (tetracycline, erythromycin and ciprofloxacin) and one in vivo (erythromycin).

Results

We show that in vitro OMKO1 can reduce antibiotic resistance of P. aeruginosa (Washington PAO1) even in the presence of antibiotics, an effect still detectable after ca.70 bacterial generations in continuous culture with phage. Our in vivo experiment showed that phage both increased the survival times of wax moth larvae (Galleria mellonella) and increased bacterial sensitivity to erythromycin. This increased antibiotic sensitivity occurred both in lines with and without the antibiotic.

Conclusions and implications

Our study supports a trade-off between antibiotic resistance and phage sensitivity. This trade-off was maintained over co-evolutionary time scales even under combined phage and antibiotic pressure. Similarly, OMKO1 maintained this trade-off in vivo, again under dual phage/antibiotic pressure. Our findings have implications for the future clinical use of steering in phage therapies. Lay Summary: Given the rise of antibiotic-resistant bacterial infection, new approaches to treatment are urgently needed. Bacteriophages (phages) are bacterial viruses. The use of such viruses to treat infections has been in near-continuous use in several countries since the early 1900s. Recent developments have shown that these viruses are not only effective against routine infections but can also target antibiotic resistant bacteria in a novel, unexpected way. Similar to other lytic phages, these so-called 'steering phages' kill the majority of bacteria directly. However, steering phages also leave behind bacterial variants that resist the phages, but are now sensitive to antibiotics. Treatment combinations of these phages and antibiotics can now be used to greater effect than either one independently. We evaluated the impact of steering using phage OMKO1 and a panel of three antibiotics on Pseudomonas aeruginosa, an important pathogen in hospital settings and in people with cystic fibrosis. Our findings indicate that OMKO1, either alone or in combination with antibiotics, maintains antibiotic sensitivity both in vitro and in vivo, giving hope that phage steering will be an effective treatment option against antibiotic-resistant bacteria.