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

Extensively and multidrug-resistant bacterial strains: case studies of antibiotics resistance

The development of antibiotic resistance compromises the effectiveness of our most effective defenses against bacterial infections, presenting a threat to global health. To date, a large number of research articles exist in the literature describing the case reports associated with extensively drug-resistant (XDR) and multidrug-resistant (MDR) bacterial strains. However, these findings are scattered, making it time-consuming for researchers to locate promising results and there remains a need for a comparative study to compile these case reports from various geographical regions including the Kingdom of Saudi Arabia. Additionally, no study has yet been published that compares the genetic variations and case reports of MDR and XDR strains identified from Saudi Arabia, the Middle East, Central Europe, and Asian countries. This study attempts to provide a comparative analysis of several MDR and XDR case reports from Saudi Arabia alongside other countries. Furthermore, the purpose of this work is to demonstrate the genetic variations in the genes underlying the resistance mechanisms seen in MDR and XDR bacterial strains that have been reported in Saudi Arabia and other countries. To cover the gap, this comprehensive review explores the complex trends in antibiotic resistance and the growing risk posed by superbugs. We provide context on the concerning spread of drug-resistant bacteria by analyzing the fundamental mechanisms of antibiotic resistance and looking into individual case reports. In this article, we compiled various cases and stories associated with XDR and MDR strains from Saudi Arabia and various other countries including China, Egypt, India, Poland, Pakistan, and Taiwan. This review will serve as basis for highlighting the growing threat of MDR, XDR bacterial strains in Saudi Arabia, and poses the urgent need for national action plans, stewardship programs, preventive measures, and novel antibiotics research in the Kingdom.

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.

Ciprofloxacin-Loaded Inhalable Formulations against Lower Respiratory Tract Infections: Challenges, Recent Advances, and Future Perspectives

Inhaled ciprofloxacin (CFX) has been investigated as a treatment for lower respiratory tract infections (LRTIs) associated with cystic fibrosis (CF), chronic obstructive pulmonary disease (COPD), and bronchiectasis. The challenges in CFX effectiveness for LRTI treatment include poor aqueous solubility and therapy resistance. CFX dry powder for inhalation (DPI) formulations were well-tolerated, showing a remarkable decline in overall bacterial burden compared to a placebo in bronchiectasis patients. Recent research using an inhalable powder combining Pseudomonas phage PEV20 with CFX exhibited a substantial reduction in bacterial density in mouse lungs infected with clinical P. aeruginosa strains and reduced inflammation. Currently, studies suggest that elevated biosynthesis of fatty acids could serve as a potential biomarker for detecting CFX resistance in LRTIs. Furthermore, inhaled CFX has successfully addressed various challenges associated with traditional CFX, including the incapacity to eliminate the pathogen, the recurrence of colonization, and the development of resistance. However, further exploration is needed to address three key unresolved issues: identifying the right patient group, determining the optimal treatment duration, and accurately assessing the risk of antibiotic resistance, with additional multicenter randomized controlled trials suggested to tackle these challenges. Importantly, future investigations will focus on the effectiveness of CFX DPI in bronchiectasis and COPD, aiming to differentiate prognoses between these two conditions. This review underscores the importance of CFX inhalable formulations against LRTIs in preclinical and clinical sectors, their challenges, recent advancements, and future perspectives.

Exploring the dynamics of mixed-species biofilms involving Candida spp. and bacteria in cystic fibrosis

Cystic fibrosis (CF) is an inherited disease that results from mutations in the gene responsible for the cystic fibrosis transmembrane conductance regulator (CFTR). The airways become clogged with thick, viscous mucus that traps microbes in respiratory tracts, facilitating colonization, inflammation and infection. CF is recognized as a biofilm-associated disease, it is commonly polymicrobial and can develop in biofilms. This review discusses Candida spp. and both Gram-positive and Gram-negative bacterial biofilms that affect the airways and cause pulmonary infections in the CF context, with a particular focus on mixed-species biofilms. In addition, the review explores the intricate interactions between fungal and bacterial species within these biofilms and elucidates the underlying molecular mechanisms that govern their dynamics. Moreover, the review addresses the multifaceted issue of antimicrobial resistance in the context of CF-associated biofilms. By synthesizing current knowledge and research findings, this review aims to provide insights into the pathogenesis of CF-related infections and identify potential therapeutic approaches to manage and combat these complex biofilm-mediated infections.

An effective antibiofilm strategy based on bacteriophages armed with silver nanoparticles

The emerging antibiotic resistance in pathogenic bacteria is a key problem in modern medicine that has led to a search for novel therapeutic strategies. A potential approach for managing such bacteria involves the use of their natural killers, namely lytic bacteriophages. Another effective method involves the use of metal nanoparticles with antimicrobial properties. However, the use of lytic phages armed with nanoparticles as an effective antimicrobial strategy, particularly with respect to biofilms, remains unexplored. Here, we show that T7 phages armed with silver nanoparticles exhibit greater efficacy in terms of controlling bacterial biofilm, compared with phages or nanoparticles alone. We initially identified a novel silver nanoparticle-binding peptide, then constructed T7 phages that successfully displayed the peptide on the outer surface of the viral head. These recombinant, AgNP-binding phages could effectively eradicate bacterial biofilm, even when used at low concentrations. Additionally, when used at concentrations that could eradicate bacterial biofilm, T7 phages armed with silver nanoparticles were not toxic to eukaryotic cells. Our results show that the novel combination of lytic phages with phage-bound silver nanoparticles is an effective, synergistic and safe strategy for the treatment of bacterial biofilms.

Phage therapy: breathing new tactics into lower respiratory tract infection treatments

Lower respiratory tract infections (LRTIs) present a significant global health burden, exacerbated by the rise in antimicrobial resistance (AMR). The persistence and evolution of multidrug-resistant bacteria intensifies the urgency for alternative treatments. This review explores bacteriophage (phage) therapy as an innovative solution to combat bacterial LRTIs. Phages, abundant in nature, demonstrate specificity towards bacteria, minimal eukaryotic toxicity, and the ability to penetrate and disrupt bacterial biofilms, offering a targeted approach to infection control. The article synthesises evidence from systematic literature reviews spanning 2000-2023, in vitro and in vivo studies, case reports and ongoing clinical trials. It highlights the synergistic potential of phage therapy with antibiotics, the immunophage synergy in animal models, and the pharmacodynamics and pharmacokinetics critical for clinical application. Despite promising results, the article acknowledges that phage therapy is at a nascent stage in clinical settings, the challenges of phage-resistant bacteria, and the lack of comprehensive cost-effectiveness studies. It stresses the need for further research to optimise phage therapy protocols and navigate the complexities of phage-host interactions, particularly in vulnerable populations such as the elderly and immunocompromised. We call for regulatory adjustments to facilitate the exploration of the long-term effects of phage therapy, aiming to incorporate this old-yet-new therapy into mainstream clinical practice to tackle the looming AMR crisis.

Optimizing in vitro phage-ciprofloxacin combination formulation for respiratory therapy of multi-drug resistant Pseudomonas aeruginosa infections

Respiratory infection caused by multi-drug resistant (MDR) Pseudomonas aeruginosa is challenging to treat. In this study, we investigate the optimal dose of anti-pseudomonas phage PEV31 (103, 105, and 108 PFU/mL) combined with ciprofloxacin (ranging from 1/8× MIC to 8× MIC) to treat the MDR P. aeruginosa strain FADD1-PA001 using time-kill studies. We determined the impact of phage growth kinetics in the presence of ciprofloxacin through one-step growth analysis. Single treatments with either phage PEV31 or ciprofloxacin (except at 8× MIC) showed limited bactericidal efficiency, with bacterial regrowth observed at 48 h. The most effective treatments were PEV31 at multiplicity of infection (MOI) of 0.1 and 100 combined with ciprofloxacin at concentrations above 1× MIC, resulting in a >4 log10 reduction in bacterial counts. While the burst size of phage PEV31 was decreased with increasing ciprofloxacin concentration, robust antimicrobial effects were still maintained in the combination treatment. Aerosol samples collected from vibrating mesh nebulization of the combination formulation at phage MOI of 100 with 2× MIC effectively inhibited bacterial density. In summary, our combination treatments eradicated in vitro bacterial growth and sustained antimicrobial effects for 48 h. These results indicated the potential application of nebulization-based strategies for the combination treatment against MDR lung infections.

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

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

Stability Considerations for Bacteriophages in Liquid Formulations Designed for Nebulization

Pulmonary bacterial infections present a significant health risk to those with chronic respiratory diseases (CRDs) including cystic fibrosis (CF) and chronic-obstructive pulmonary disease (COPD). With the emergence of antimicrobial resistance (AMR), novel therapeutics are desperately needed to combat the emergence of resistant superbugs. Phage therapy is one possible alternative or adjunct to current antibiotics with activity against antimicrobial-resistant pathogens. How phages are administered will depend on the site of infection. For respiratory infections, a number of factors must be considered to deliver active phages to sites deep within the lung. The inhalation of phages via nebulization is a promising method of delivery to distal lung sites; however, it has been shown to result in a loss of phage viability. Although preliminary studies have assessed the use of nebulization for phage therapy both in vitro and in vivo, the factors that determine phage stability during nebulized delivery have yet to be characterized. This review summarizes current findings on the formulation and stability of liquid phage formulations designed for nebulization, providing insights to maximize phage stability and bactericidal activity via this delivery method.

Bacteriophages: The promising therapeutic approach for enhancing ciprofloxacin efficacy against bacterial infection

BACKGROUND

The emergence of ciprofloxacin-resistant bacteria is a serious challenge worldwide, bringing the need to find new approaches to manage this bacterium. Bacteriophages (phages) have been shown inhibitory effects against ciprofloxacin-resistance bacteria; thus, ciprofloxacin resistance or tolerance may not affect the phage's infection ability. Additionally, researchers used phage-ciprofloxacin combination therapy for the inhibition of multidrug-resistant bacteria.

RESULTS

The sublethal concentrations of ciprofloxacin could lead to an increase in progeny production. Antibiotic treatments could enhance the release of progeny phages by shortening the lytic cycle and latent period. Thus, sublethal concentrations of antibiotics combined with phages can be used for the management of bacterial infections with high antibiotic resistance. In addition, combination therapy exerts various selection pressures that can mutually decrease phage and antibiotic resistance. Moreover, phage ciprofloxacin could significantly reduce bacterial counts in the biofilm community. Immediate usage of phages after the attachment of bacteria to the surface of the flow cells, before the development of micro-colonies, could lead to the best effect of phage therapy against bacterial biofilm. Noteworthy, phage should be used before antibiotics usage because this condition may have allowed phage replication to occur first before ciprofloxacin interrupted the bacterial DNA replication process, thereby interfering with the activity of the phages. Furthermore, the phage-ciprofloxacin combination showed a promising result for the management of Pseudomonas aeruginosa infections in mouse models. Nevertheless, low data are existing about the interaction between phages and ciprofloxacin in combination therapies, especially regarding the emergence of phage-resistant mutants. Additionally, there is a challenging and important question of how the combined ciprofloxacin with phages can increase antibacterial functions. Therefore, more examinations are required to support the clinical usage of phage-ciprofloxacin combination therapy.

Bacteriophage-Antibiotic Combination Therapy against Pseudomonas aeruginosa

Phage therapy is an alternative therapy that is being used as the last resource against infections caused by multidrug-resistant bacteria after the failure of standard treatments. Pseudomonas aeruginosa can cause pneumonia, septicemia, urinary tract, and surgery site infections mainly in immunocompromised people, although it can cause infections in many different patient profiles. Cystic fibrosis patients are particularly vulnerable. In vitro and in vivo studies of phage therapy against P. aeruginosa include both bacteriophages alone and combined with antibiotics. However, the former is the most promising strategy utilized in clinical infections. This review summarizes the recent studies of phage-antibiotic combinations, highlighting the synergistic effects of in vitro and in vivo experiments and successful treatments in patients.

Pulmonary bacteriophage and cystic fibrosis airway mucus: friends or foes?

For those born with cystic fibrosis (CF), hyper-concentrated mucus with a dysfunctional structure significantly impacts CF airways, providing a perfect environment for bacterial colonization and subsequent chronic infection. Early treatment with antibiotics limits the prevalence of bacterial pathogens but permanently alters the CF airway microenvironment, resulting in antibiotic resistance and other long-term consequences. With little investment into new traditional antibiotics, safe and effective alternative therapeutic options are urgently needed. One gathering significant traction is bacteriophage (phage) therapy. However, little is known about which phages are effective for respiratory infections, the dynamics involved between phage(s) and the host airway, and associated by-products, including mucus. Work utilizing gut cell models suggest that phages adhere to mucus components, reducing microbial colonization and providing non-host-derived immune protection. Thus, phages retained in the CF mucus layer result from the positive selection that enables them to remain in the mucus layer. Phages bind weakly to mucus components, slowing down the diffusion motion and increasing their chance of encountering bacterial species for subsequent infection. Adherence of phage to mucus could also facilitate phage enrichment and persistence within the microenvironment, resulting in a potent phage phenotype or vice versa. However, how the CF microenvironment responds to phage and impacts phage functionality remains unknown. This review discusses CF associated lung diseases, the impact of CF mucus, and chronic bacterial infection. It then discusses the therapeutic potential of phages, their dynamic relationship with mucus and whether this may enhance or hinder airway bacterial infections in CF.

In vitro antibacterial effects of combination of ciprofloxacin with compounds isolated from Streptomyces luteireticuli NIIST-D75

Three phenazines, 1-methoxyphenazine (1), methyl-6-methoxyphenazine-1-carboxylate (2), 1,6-dimethoxyphenazine (4), and a 2,3-dimethoxy benzamide (3) were isolated from the Streptomyces luteireticuli NIIST-D75, and the antibacterial effects of compounds 1-3, each in combination with ciprofloxacin, were investigated. The in vitro antibacterial activity was assessed by microdilution, checkerboard, and time-kill assay against Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa, and Salmonella typhi. According to the checkerboard assay results, each combination of compounds 1, 2 and 3 with ciprofloxacin resulted in a significantly lower minimum inhibitory concentrations (MICs) of 0.02-1.37 µg ml-1, suggesting synergistic combinations by fractional inhibitory concentration index, and displayed bactericidal activity in time-kill kinetics within 48 h. SEM analysis was carried out to determine the changes in morphology in S. aureus and E. coli during treatment with individual combination of ciprofloxacin and compounds (1-3), which revealed drastic changes in the cells such as dent formation, biofilm disruption, cell bursting, and doughnut-like formation, change in surface morphology in S. aureus, and cell elongation, cell burst with ruptured cell, and change in surface morphology in E. coli. Hep G2 cell viability was not affected by the compounds (1-3) that were tested for cytotoxicity up to 250 µM.

Design of Phage-Cocktail-Containing Hydrogel for the Treatment of Pseudomonas aeruginosa-Infected Wounds

Recently, the treatment of infected wounds has become a global problem due to increased antibiotic resistance in bacteria. The Gram-negative opportunistic pathogen Pseudomonas aeruginosa is often present in chronic skin infections, and it has become a threat to public health as it is increasingly multidrug resistant. Due to this, new measures to enable treatment of infections are necessary. Treatment of bacterial infections with bacteriophages, known as phage therapy, has been in use for a century, and has potential with its antimicrobial effect. The main purpose of this study was to create a phage-containing wound dressing with the ability to prevent bacterial infection and rapid wound healing without side effects. Several phages against P. aeruginosa were isolated from wastewater, and two polyvalent phages were used to prepare a phage cocktail. The phage cocktail was loaded in a hydrogel composed of polymers of sodium alginate (SA) and carboxymethyl cellulose (CMC). To compare the antimicrobial effects, hydrogels containing phages, ciprofloxacin, or phages plus ciprofloxacin were produced, and hydrogels without either. The antimicrobial effect of these hydrogels was investigated in vitro and in vivo using an experimental mouse wound infection model. The wound-healing process in different mouse groups showed that phage-containing hydrogels and antibiotic-containing hydrogels have almost the same antimicrobial effect. However, in terms of wound healing and pathological process, the phage-containing hydrogels performed better than the antibiotic alone. The best performance was achieved with the phage-antibiotic hydrogel, indicating a synergistic effect between the phage cocktail and the antibiotic. In conclusion, phage-containing hydrogels eliminate efficiently P. aeruginosa in wounds and may be a proper option for treating infectious wounds.

Drug Combination of Ciprofloxacin and Polymyxin B for the Treatment of Multidrug–Resistant Acinetobacter baumannii Infections: A Drug Pair Limiting the Development of Resistance

Polymyxins are considered as last–resort antibiotics to treat infections caused by Acinetobacter baumannii. However, there are increasing reports of resistance in A. baumannii to polymyxins. In this study, inhalable combinational dry powders consisting of ciprofloxacin (CIP) and polymyxin B (PMB) were prepared by spray–drying. The obtained powders were characterized with respect to the particle properties, solid state, in vitro dissolution and in vitro aerosol performance. The antibacterial effect of the combination dry powders against multidrug–resistant A. baumannii was assessed in a time–kill study. Mutants from the time–kill study were further investigated by population analysis profiling, minimum inhibitory concentration testing, and genomic comparisons. Inhalable dry powders consisting of CIP, PMB and their combination showed a fine particle fraction above 30%, an index of robust aerosol performance of inhaled dry powder formulations in the literature. The combination of CIP and PMB exhibited a synergistic antibacterial effect against A. baumannii and suppressed the development of CIP and PMB resistance. Genome analyses revealed only a few genetic differences of 3–6 SNPs between mutants and the progenitor isolate. This study suggests that inhalable spray–dried powders composed of the combination of CIP and PMB is promising for the treatment of respiratory infections caused by A. baumannii, and this combination can enhance the killing efficiency and suppress the development of drug resistance.

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

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

The resistance mechanisms of bacteria against ciprofloxacin and new approaches for enhancing the efficacy of this antibiotic

For around three decades, the fluoroquinolone (FQ) antibiotic ciprofloxacin has been used to treat a range of diseases, including chronic otorrhea, endocarditis, lower respiratory tract, gastrointestinal, skin and soft tissue, and urinary tract infections. Ciprofloxacin's main mode of action is to stop DNA replication by blocking the A subunit of DNA gyrase and having an extra impact on the substances in cell walls. Available in intravenous and oral formulations, ciprofloxacin reaches therapeutic concentrations in the majority of tissues and bodily fluids with a low possibility for side effects. Despite the outstanding qualities of this antibiotic, Salmonella typhi, Staphylococcus aureus, Escherichia coli, and Pseudomonas aeruginosa have all shown an increase in ciprofloxacin resistance over time. The rise of infections that are resistant to ciprofloxacin shows that new pharmacological synergisms and derivatives are required. To this end, ciprofloxacin may be more effective against the biofilm community of microorganisms and multi-drug resistant isolates when combined with a variety of antibacterial agents, such as antibiotics from various classes, nanoparticles, natural products, bacteriophages, and photodynamic therapy. This review focuses on the resistance mechanisms of bacteria against ciprofloxacin and new approaches for enhancing its efficacy.

The Selection of Antibiotic- and Bacteriophage-Resistant Pseudomonas aeruginosa Is Prevented by Their Combination

Bacteria developing resistance compromise the efficacy of antibiotics or bacteriophages (phages). We tested the association of these two antibacterials to circumvent resistance. With the Hollow Fiber Infection Model (HFIM), we mimicked the concentration profile of ciprofloxacin in the lungs of patients treated orally for Pseudomonas aeruginosa infections and, independently, mimicked a single inhaled administration of phages (one or two phages). Each treatment selects for antibiotic- or phage-resistant clones in less than 30 h. In contrast, no bacteria were recovered from the HFIM at 72 h when ciprofloxacin was started 4 h post phage administration, even when increasing the initial bacterial concentration by 1,000-fold. The combination of phages with antibiotics used according to clinical regimens prevents the growth of resistant clones, providing opportunities to downscale the use of multiple antibiotics. IMPORTANCE In the treatment of bacterial infections, the use of antibiotics or bacteriophages (phages) is limited by the ability of bacteria to develop resistance. The resistance frequency depends on the exposure to antibacterials. Therefore, determination of concentration profiles of antibiotics is key to define optimal regimens during treatments. In the laboratory, the Hollow Fiber Infection Model (HFIM) mimics concentration profiles observed in patients. In this study, we used the HFIM to evaluate the killing efficacy of the combination of phages and ciprofloxacin. We demonstrated that dosing schedule of phages first and the antibiotic second prevent the selection of resistant bacteria. These results demonstrate that combination efficacy relies on a strong initial reduction of the bacterial population by phages followed by antibiotics before any resistant arise.

Enhancing the Stability of Bacteriophages Using Physical, Chemical, and Nano-Based Approaches: A Review

Phages are efficient in diagnosing, treating, and preventing various diseases, and as sensing elements in biosensors. Phage display alone has gained attention over the past decade, especially in pharmaceuticals. Bacteriophages have also found importance in research aiming to fight viruses and in the consequent formulation of antiviral agents and vaccines. All these applications require control over the stability of virions. Phages are considered resistant to various harsh conditions. However, stability-determining parameters are usually the only additional factors in phage-related applications. Phages face instability and activity loss when preserved for extended periods. Sudden environmental changes, including exposure to UV light, temperature, pH, and salt concentration, also lead to a phage titer fall. This review describes various formulations that impart stability to phage stocks, mainly focusing on polymer-based stabilization, encapsulation, lyophilization, and nano-assisted solutions.

Characterization of a Lytic Bacteriophage vB_SurP-PSU3 Infecting Staphylococcus ureilyticus and Its Efficacy Against Biofilm

In response to the increasing nosocomial infections caused by antimicrobial-resistant coagulase-negative staphylococci (CoNS), bacteriophages (phages) have emerged as an alternative to antibiotics. Staphylococcus ureilyticus, one of the representative species of the CoNS, is now considered a notable pathogen that causes nosocomial bloodstream infections, and its biofilm-forming ability increases pathogenicity and resistance to antimicrobial agents. In this study, a lytic phage infecting S. ureilyticus was newly isolated from wastewater collected from a sewage treatment plant and its biological and antimicrobial characteristics are described. The isolated phage, named vB_SurP-PSU3, was morphologically similar to Podoviridae and could simultaneously lyse some S. warneri strains used in this study. The sequenced genome of the phage consisted of linear dsDNA with 18,146 bp and genome-based phylogeny revealed that vB_SurP-PSU3 belonged to the genus Andhravirus. Although its overall genomic arrangement and contents were similar to those of other members of the Andhravirus, the predicted endolysin of vB_SurP-PSU3 distinctly differed from the other members of the genus. The bacteriolytic activity of vB_SurP-PSU3 was evaluated using S. ureilyticus ATCC 49330, and the phage could efficiently inhibit the planktonic growth of the bacteria. Moreover, the anti-biofilm analysis showed that vB_SurP-PSU3 could prevent the formation of bacterial biofilm and degrade the mature biofilm in vitro. In an additional cytotoxicity assay of vB_SurP-PSU3, no significant adverse effects were observed on the tested cell. Based on these findings, the newly isolated phage vB_SurP-PSU3 could be classified as a new member of Andhravirus and could be considered an alternative potential biocontrol agent against S. ureilyticus infections and its biofilm.

Characterization of Pseudomonas aeruginosa Bacteriophage L5 Which Requires Type IV Pili for Infection

Pseudomonas aeruginosa is a common opportunistic human pathogen. With the emergence of multidrug-resistant (MDR) clinical infection of P. aeruginosa, phage therapy has received renewed attention in treating P. aeruginosa infections. Moreover, a detailed understanding of the host receptor of lytic phage is crucial for selecting proper phages for therapy. Here, we describe the characterization of the P. aeruginosa bacteriophage L5 with a double-stranded DNA genome of 42,925 bp. The genomic characteristics indicate that L5 is a lytic bacteriophage belonging to the subfamily Autographivirinae. In addition, the phage receptors for L5 were also identified as type IV pili, because the mutation of pilZ, which is involved in pili synthesis, resists phage infection, while the complementation of pilZ restored its phage sensitivity. This research reveals that L5 is a potential phage therapy candidate for the treatment of P. aeruginosa infection.

Novel antimicrobial agents for combating antibiotic-resistant bacteria

Antibiotic therapy has become increasingly ineffective against bacterial infections due to the rise of resistance. In particular, ESKAPE pathogens (Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, and Enterobacter species) have caused life-threatening infections in humans and represent a major global health threat due to a high degree of antibiotic resistance. To respond to this urgent call, novel strategies are urgently needed, such as bacteriophages (or phages), phage-encoded enzymes, immunomodulators and monoclonal antibodies. This review critically analyses these promising antimicrobial therapies for the treatment of multidrug-resistant bacterial infections. Recent advances in these novel therapeutic strategies are discussed, focusing on preclinical and clinical investigations, as well as combinatorial approaches. In this 'Bad Bugs, No Drugs' era, novel therapeutic strategies can play a key role in treating deadly infections and help extend the lifetime of antibiotics.

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.

Phage–Antibiotic Therapy as a Promising Strategy to Combat Multidrug-Resistant Infections and to Enhance Antimicrobial Efficiency

Infections caused by multidrug-resistant (MDR) bacteria have highlighted the importance of the development of new antimicrobial agents. While bacteriophages (phages) are widely studied as alternative agents to antibiotics, combined treatments using phages and antibiotics have exhibited Phage–Antibiotic Synergy (PAS), in which antibiotics promote phage replication and extraordinary antimicrobial efficacy with reduced development of bacterial resistance. This review paper on the current progress of phage–antibiotic therapy includes aspects of the mechanisms of PAS and the therapeutic performance of PAS in combating multidrug-resistant bacterial infections. The choice of phages and antibiotics, the administration time and sequence, and the concentrations of the two agents impact the bacterial inhibitory effects to different extents.

Bacteriophages and antibiotic interactions in clinical practice: what we have learned so far

Bacteriophages (phages) may be used as an alternative to antibiotic therapy for combating infections caused by multidrug-resistant bacteria. In the last decades, there have been studies concerning the use of phages and antibiotics separately or in combination both in animal models as well as in humans. The phenomenon of phage–antibiotic synergy, in which antibiotics may induce the production of phages by bacterial hosts has been observed. The potential mechanisms of phage and antibiotic synergy was presented in this paper. Studies of a biofilm model showed that a combination of phages with antibiotics may increase removal of bacteria and sequential treatment, consisting of phage administration followed by an antibiotic, was most effective in eliminating biofilms. In vivo studies predominantly show the phenomenon of phage and antibiotic synergy. A few studies also describe antagonism or indifference between phages and antibiotics. Recent papers regarding the application of phages and antibiotics in patients with severe bacterial infections show the effectiveness of simultaneous treatment with both antimicrobials on the clinical outcome.

The effects of different doses of inhaled bacteriophage therapy for Pseudomonas aeruginosa pulmonary infections in mice

OBJECTIVES

Inhaled phage therapy has been revisited as a potential treatment option for respiratory infections caused by multidrug-resistant (MDR) Pseudomonas aeruginosa; however, there is a distinct gap in understanding the dose-response effect. The aim of this study was to investigate the dose-response effect of Pseudomonas-targeting phage PEV31 delivered by pulmonary route in a mouse lung infection model.

METHODS

Neutropenic BALB/c mice were infected with MDR P. aeruginosa (2×10⁴ colony forming units) through intra-tracheal route and then treated with PEV31 at three different doses of 7.5×10⁴ (Group A), 5×10⁶ (Group B) and 5×10⁸ (Group C) plaque forming units, or phosphate-buffered saline at 2-h post-inoculation. Mice (n=5-7) were sacrificed at 2-h and 24-h post-infection and lungs, kidneys, spleen, liver, bronchoalveolar lavage fluid and blood were collected for bacteria and phage enumeration.

RESULTS

At 24-h post-infection, all the phage-treated groups exhibited a significant reduction in pulmonary bacterial load by 1.3-1.9 log₁₀ independent of the delivered phage dose. The extent of phage replication was negatively correlated with the dose administered with log₁₀ titre increases of 6.2, 2.7 and 9 for Groups A, B and C, respectivelyPhage-resistant bacterial subpopulations in the lung homogenate samples harvested at 24-h post-infection increased with the treatment dose (i.e., 30%, 74% and 91% in respective Groups A-C). However, the emerged mutants showed increased susceptibility to ciprofloxacin, impaired twitching motility, and reduced blue-green pigment production. The expression of the inflammatory cytokines (IL-1β and IL-6 and TNF-α) was suppressed with increasing PEV31 treatment dose.

CONCLUSIONS

This study provides dose-response effect of inhaled phage therapy that may guide dose selection for treating P. aeruginosa respiratory infections in humans.

New Antibiotics for Hospital-Acquired Pneumonia and Ventilator-Associated Pneumonia

Hospital-acquired pneumonia (HAP) and ventilator-associated pneumonia (VAP) represent one of the most common hospital-acquired infections, carrying a significant morbidity and risk of mortality. Increasing antibiotic resistance among the common bacterial pathogens associated with HAP and VAP, especially Enterobacterales and nonfermenting gram-negative bacteria, has made the choice of empiric treatment of these infections increasingly challenging. Moreover, failure of initial empiric therapy to cover the causative agents associated with HAP and VAP has been associated with worse clinical outcomes. This review provides an overview of antibiotics newly approved or in development for the treatment of HAP and VAP. The approved antibiotics include ceftobiprole, ceftolozane-tazobactam, ceftazidime-avibactam, meropenem-vaborbactam, imipenem-relebactam, and cefiderocol. Their major advantages include their high activity against multidrug-resistant gram-negative pathogens.

Inhaled Delivery of Anti-Pseudomonal Phages to Tackle Respiratory Infections Caused by Superbugs

Background: Respiratory infections are increasingly difficult to treat due to the emergence of multidrug-resistant bacteria. Rediscovery and implementation of inhaled bacteriophage (phage) therapy as a standalone or supplement to antibiotic therapy is becoming recognized as a promising solution to combating respiratory infections caused by these superbugs. To ensure maximum benefit of the treatment, phages must remain stable during formulation as a liquid or powder and delivery using a nebulizer or dry powder inhaler. Methods: Pseudomonas-targeting PEV phages were used as model phages to assess the feasibility of aerosolizing biologically viable liquid formulations using commercial nebulizers in the presence and absence of inhaled antibiotics. The advantages of powder formulations were exploited by spray drying to produce inhalable powders containing PEV phages with and without the antibiotic ciprofloxacin. Results: The produced phage PEV20 and PEV20-ciprofloxacin powders remained stable over long-term storage and exhibited significant bacterial killing activities in a mouse lung infection model. Conclusion: These studies demonstrated that inhaled phage (-antibiotic) therapy has the potential to tackle respiratory infections caused by superbugs.

Prospects of Inhaled Phage Therapy for Combatting Pulmonary Infections

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

Developing ciprofloxacin dry powder for inhalation: A story of challenges and rational design in the treatment of cystic fibrosis lung infection

Cystic fibrosis (CF) is an inherited multisystem disease affecting the lung which leads to a progressive decline in lung function as a result of malfunctioning mucociliary clearance and subsequent chronic bacterial infections. Pseudomonas aeruginosa is the predominant cause of lung infection in CF patients and is associated with significant morbidity and mortality. Thus, antibiotic therapy remains the cornerstone of the treatment of CF. Pulmonary delivery of antibiotics for lung infections significantly reduces the required dose and the associated systemic side effects while improving therapeutic outcomes. Ciprofloxacin is one of the most widely used antibiotics against P. aeruginosa and the most effective fluoroquinolone. However, in spite of the substantial amount of research aimed at developing ciprofloxacin powder for inhalation, none of these formulations has been commercialized. Here, we present an integrated view of the diverse challenges associated with delivering ciprofloxacin dry particles to the lungs of CF patients and the rationales behind recent formulations of ciprofloxacin dry powder for inhalation. This review will discuss the challenges in developing ciprofloxacin powder for inhalation along with the physiological and pathophysiological challenges such as ciprofloxacin lung permeability, overproduction of viscous mucus and bacterial biofilms. The review will also discuss the current and emerging particle engineering approaches to overcoming these challenges. By doing so, we believe the review will help the reader to understand the current limitations in developing an inhalable ciprofloxacin powder and explore new opportunities of rational design strategies.

Expanding clinical phage microbiology: simulating phage inhalation for respiratory tract infections

Phage therapy is a promising antibacterial strategy for resistant respiratory tract infections. Phage inhalation may serve this goal; however, it requires a careful assessment of their delivery by this approach. Here we present an in vitro model to evaluate phage inhalation. Eight phages, most of which target pathogens common in cystic fibrosis, were aerosolised by jet nebuliser and administered to a real-scale computed tomography-derived 3D airways model with a breathing simulator. Viable phage loads reaching the output of the nebuliser and the tracheal level of the model were determined and compared to the loaded amount. Phage inhalation resulted in a diverse range of titre reduction, primarily associated with the nebulisation process. No correlation was found between phage delivery to the phage physical or genomic dimensions. These findings highlight the need for tailored simulations of phage delivery, ideally by a patient-specific model in addition to proper phage matching, to increase the potential of phage therapy success.

Current and Emerging Therapies to Combat Cystic Fibrosis Lung Infections

The ultimate aim of any antimicrobial treatment is a better infection outcome for the patient. Here, we review the current state of treatment for bacterial infections in cystic fibrosis (CF) lung while also investigating potential new treatments being developed to see how they may change the dynamics of antimicrobial therapy. Treatment with antibiotics coupled with regular physical therapy has been shown to reduce exacerbations and may eradicate some strains. Therapies such as hypertonic saline and inhaled PulmozymeTM (DNase-I) improve mucus clearance, while modifier drugs, singly and more successfully in combination, re-open certain mutant forms of the cystic fibrosis transmembrane conductance regulator (CFTR) to enable ion passage. No current method, however, completely eradicates infection, mainly due to bacterial survival within biofilm aggregates. Lung transplants increase lifespan, but reinfection is a continuing problem. CFTR modifiers normalise ion transport for the affected mutations, but there is conflicting evidence on bacterial clearance. Emerging treatments combine antibiotics with novel compounds including quorum-sensing inhibitors, antioxidants, and enzymes, or with bacteriophages, aiming to disrupt the biofilm matrix and improve antibiotic access. Other treatments involve bacteriophages that target, infect and kill bacteria. These novel therapeutic approaches are showing good promise in vitro, and a few have made the leap to in vivo testing.

Advances in Bacteriophage Therapy against Relevant MultiDrug-Resistant Pathogens

The increase of multiresistance in bacteria and the shortage of new antibiotics in the market is becoming a major public health concern. The World Health Organization (WHO) has declared critical priority to develop new antimicrobials against three types of bacteria: carbapenem-resistant A. baumannii, carbapenem-resistant P. aeruginosa and carbapenem-resistant and ESBL-producing Enterobacteriaceae. Phage therapy is a promising alternative therapy with renewed research in Western countries. This field includes studies in vitro, in vivo, clinical trials and clinical cases of patients receiving phages as the last resource after failure of standard treatments due to multidrug resistance. Importantly, this alternative treatment has been shown to be more effective when administered in combination with antibiotics, including infections with biofilm formation. This review summarizes the most recent studies of this strategy in animal models, case reports and clinical trials to deal with infections caused by resistant A. baumannii, K. pneumoniae, E. coli, and P. aeruginosa strains, as well as discusses the main limitations of phage therapy.

Bacteriophage-Delivering Hydrogels: Current Progress in Combating Antibiotic Resistant Bacterial Infection

Antibiotic resistance remains as an unresolved global challenge in the health care system, posing serious threats to global health. As an alternative to antibiotics, bacteriophage (phage) therapy is rising as a key to combating antibiotic-resistant bacterial infections. In order to deliver a phage to the site of infection, hydrogels have been formulated to incorporate phages, owing to its favorable characteristics in delivering biological molecules. This paper reviews the formulation of phage-delivering hydrogels for orthopedic implant-associated bone infection, catheter-associated urinary tract infection and trauma-associated wound infection, with a focus on the preparation methods, stability, efficacy and safety of hydrogels as phage carriers.