Phage cocktail powder for Pseudomonas aeruginosa respiratory infections

Phage formulations and delivery strategies: Unleashing the potential against antibiotic-resistant bacteria

Bacterial control promoted by bacteriophages (phages) is an attractive tool in the face of the antibiotic crisis triggered by the exacerbated use of these drugs. Despite the growing interest in using these viruses, some gaps still need answers, such as the protection and delivery of phages. Some limitation points involve the degradation of phage proteins by enzymes or inactivation in low-pH environments. In this review, a literature search using keywords related to the field of virus delivery formulations was done to understand the current scenario of using delivery techniques and phage formulations. A total of 2096 raw results were obtained, which resulted in 140 publications after refinement. These studies were analyzed for main application techniques and areas, keywords, and countries. Of the total, 57% of the publications occurred in the last five years, and the encapsulation technique was the most used among the articles analyzed. As excipient agents, lactose, trehalose, mannitol, PEG, and Leucine stand out. The development of phage formulations, protection approaches, their delivery routes, and the knowledge about the best application strategy enables the use of these organisms in several sectors. It can act as a powerful tool against antibiotic-resistant bacteria.

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.

Phage therapy in lung infections caused by multidrug-resistant Pseudomonas aeruginosa - A literature review

Pulmonary infections of patients with cystic fibrosis (CF) or in intensive care units are frequently caused by the Gram-negative opportunistic pathogen Pseudomonas aeruginosa. Since these bacteria are commonly inherently multidrug-resistant (MDR) and hence, antibiotic treatment options are limited, bacteriophages may provide alternative therapeutic and prophylactic measures in the combat of pneumonia caused by P. aeruginosa. This prompted us to perform a comprehensive literature survey of current knowledge regarding effects of phages applied against pulmonary P. aeruginosa infections. The included 23 studies revealed that P. aeruginosa specific phages lyse and eliminate the bacteria even in case of biofilm production in vitro, whereas application to mice and men resulted in mitigated P. aeruginosa induced clinical signs and enhanced survival. Besides distinct host immune responses, no major adverse effects limiting therapeutic and/or prophylactic phage application were noted. However, the immune system and antibiotics generate synergies with phages due to the mutable sensitivity of P. aeruginosa. In conclusion, results summarized in this review provide evidence that phages constitute promising alternative treatment options for lung infections caused by MDR P. aeruginosa. Further studies are needed, however, to underscore the efficacy and safety aspects of phages application to infected patients including immune-compromised individuals.

Potential of phage depolymerase for the treatment of bacterial biofilms

Resistance of bacteria to antibiotics is a major concern in medicine and veterinary science. The bacterial biofilm structures not only prevent the penetration of drugs into cells within the biofilm's interior but also aid in evasion of the host immune system. Hence, there is an urgent need to develop novel therapeutic approaches against bacterial biofilms. One potential strategy to counter biofilms is to use phage depolymerases that degrade the matrix structure of the bacteria and enable access to bacterial cells. This review mainly discusses the methods by which phage depolymerases enhance the efficacy of the human immune system and the therapeutic applications of some phage depolymerases, such as single phage depolymerase application, combined therapy with phage depolymerase and antibiotics, and phage depolymerase cocktails, for treating bacterial biofilms. This review also summarizes the relationship between bacterial biofilms and antibiotic resistance.

Therapeutic effect and anti-biofilm ability assessment of a novel phage, phiPA1-3, against carbapenem-resistant Pseudomonas aeruginosa

Multiple drug-resistant (MDR) Pseudomonas aeruginosa commonly causes severe hospital-acquired infections. The gradual emergence of carbapenem-resistant P. aeruginosa has recently gained attention. A wide array of P. aeruginosa-mediated pathogenic mechanisms, including its biofilm-forming ability, limits the use of effective antimicrobial treatments against it. In the present study, we isolated and characterized the phenotypic, biological, and genomic characteristics of a bacteriophage, vB_PaP_phiPA1-3 (phiPA1-3). Biofilm eradication and phage rescue from bacterial infections were assessed to demonstrate the efficacy of the application potential. Host range spectrum analysis revealed that phiPA1-3 is a moderate host range phage that infects 20% of the clinically isolated strains of P. aeruginosa tested, including carbapenem-resistant P. aeruginosa (CRPA). The phage exhibited stability at pH 7.0 and 9.0, with significantly reduced viability below pH 5.0 and beyond pH 9.0. phiPA1-3 is a lytic phage with a burst size of 619 plaque-forming units/infected cell at 37 °C and can effectively lyse bacteria in a multiplicity of infection-dependent manner. The genome size of phiPA1-3 was found to be 73,402 bp, with a G+C content of 54.7%, containing 93 open reading frames, of which 62 were annotated as hypothetical proteins and the remaining 31 had known functions. The phage possesses several proteins similar to those found in N4-like phages, including three types of RNA polymerases. This study concluded that phiPA1-3 belongs to the N4-like Schitoviridae family, can potentially eradicate P. aeruginosa biofilms, and thus, serve as a valuable tool for controlling CRPA infections.

Evaluation of the Lytic Activity of Various Phage Cocktails Against, ESBL-Producer, Non-Producer and Carbapenem-Resistant Escherichia coli Isolates

Bacteriophages have been proposed as an alternative therapy for the treatment of bacterial infections. This research aims to determine the lytic activity of bacteriophage-cocktails (BC) against carbapenem-resistant (CR-EC), ESBL-producer (EP-EC), and non-producer (NP-EC) E. coli isolates. Related resistance genes in 87 E. coli isolates were screened by PCR. The efficacies of BCs were determined by spot test and lytic zones were evaluated from fully-confluent to opaque. MOIs of the BCs were compared for fully-confluent and opaque lytic zones. BCs were also evaluated in terms of their biophysical characteristics including latency, burst size, pH and temperature stabilities. Among EP-EC, 96.9% of the isolates carry blaCTX-M, 25% of them blaSHV and 15.6% of them carry blaTEM. All CR-EC isolates carried blaOXA-48, but not blaKPC and blaNDM. CR-EC isolates were the least susceptible for the each of four BCs. MOIs for ENKO, SES and INTESTI-phage forming fully-confluent zone in E. coli isolates EC3 (NP-EC), EC8 (EP-EC) and EC27 (NP-EC), respectively were 10, 100 and 1, respectively. MOIs for ENKO, SES and INTESTI opaque zone in EC19 (EP-EC), EC10 (EP-EC), EC1(NP-EC), respectively were 0.01, 0.01, 0.1 PFU/CFU, respectively. The MOI for PYO-phage forming a semi-confluent zone in EC6 (NP-EC) isolate was 1 PFU/CFU. The phages were thermally stable and tolerant to a wide pH range. Comparison of MOIs according to lysis zone characteristics demonstrated that the activities of phages in phage cocktails vary depending on the characteristics of each bacterial host.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12088-023-01074-9.

Development and Evaluation of Bacteriophage Cocktail to Eradicate Biofilms Formed by an Extensively Drug-Resistant (XDR) Pseudomonas aeruginosa

Extensive and multiple drug resistance in P. aeruginosa combined with the formation of biofilms is responsible for its high persistence in nosocomial infections. A sequential method to devise a suitable phage cocktail with a broad host range and high lytic efficiency against a biofilm forming XDR P. aeruginosa strain is presented here. Out of a total thirteen phages isolated against P. aeruginosa, five were selected on the basis of their high lytic spectra assessed using spot assay and productivity by efficiency of plating assay. Phages, after selection, were tested individually and in combinations of two-, three-, four-, and five-phage cocktails using liquid infection model. Out of total 22 combinations tested, the cocktail comprising four phages viz. φPA170, φPA172, φPA177, and φPA180 significantly inhibited the bacterial growth in liquid infection model (p < 0.0001). The minimal inhibitory dose of each phage in a cocktail was effectively reduced to >10 times than the individual dose in the inhibition of XDR P. aeruginosa host. Field emission-scanning electron microscopy was used to visualize phage cocktail mediated eradication of 4-day-old multi-layers of XDR P. aeruginosa biofilms from urinary catheters and glass cover slips, and was confirmed by absence of any viable cells. Differential bacterial inhibition was observed with different phage combinations where multiple phages were found to enhance the cocktail's lytic range, but the addition of too many phages reduced the overall inhibition. This study elaborates an effective and sequential method for the preparation of a phage cocktail and evaluates its antimicrobial potential against biofilm forming XDR strains of P. aeruginosa.

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.

Pre-treatment with phages achieved greater protection of mice against infection with Shiga toxin-producing Escherichia coli than post-treatment

Shiga toxin-producing Escherichia coli (STEC) is a group of pathogen that can cause various diseases in both humans and animals, such as watery diarrhea, hemorrhagic colitis, and uremia syndrome. Due to the serious situation of antibiotic resistance, phage therapy is considered to have a great potential in combating bacterial diseases. In this study, three phages (NJ-10, NJ-20, and NJ-38) with strong abilities to lyse virulent STEC strain CVCC193 cells in vitro were isolated. Subsequently, the therapeutic effects of the three phages were investigated in mice infected with CVCC193 cells. The results showed that the survival rates of mice injected with the phages at 3 h after challenge with CVCC193 cells were 40%-50%, while the survival rates of mice injected with the phages at 24 h before challenge were 80%-100%, indicating that pre-treatment with phages had better therapeutic effects than post-treatment. Pathological changes, bacterial loads in different organs, and serum levels of inflammatory factors of the infected mice were also detected. The results showed that the mice injected with the phages at 3 h after or 24 h before challenge with CVCC193 cells had significantly decreased organ lesions, bacterial loads, and serum levels of inflammatory factors as compared to infected mice without phage treatment. These results suggested that phages NJ-10, NJ-20, and NJ-38 can potentially protect against STEC infections.

Engineering the right formulation for enhanced drug delivery

Dry powder inhalers (DPIs) can be used with a wide range of drugs such as small molecules and biologics and offer several advantages for inhaled therapy. Early DPI products were intended to treat asthma and lung chronic inflammatory disease by administering low-dose, high-potency drugs blended with lactose carrier particles. The use of lactose blends is still the most common approach to aid powder flowability and dose metering in DPI products. However, this conventional approach may not meet the high demand for formulation physical stability, aerosolisation performance, and bioavailability. To overcome these issues, innovative techniques coupled with modification of the traditional methods have been explored to engineer particles for enhanced drug delivery. Different particle engineering techniques have been utilised depending on the types of the active pharmaceutical ingredient (e.g., small molecules, peptides, proteins, cells) and the inhaled dose. This review discusses the challenges of formulating DPI formulations of low-dose and high-dose small molecule drugs, and biologics, followed by recent and emerging particle engineering strategies utilised in developing the right inhalable powder formulations for enhanced drug delivery.

Recent developments in lactose blend formulations for carrier-based dry powder inhalation

Lactose is the most commonly used excipient in carrier-based dry powder inhalation (DPI) formulations. Numerous inhalation therapies have been developed using lactose as a carrier material. Several theories have described the role of carriers in DPI formulations. Although these theories are valuable, each DPI formulation is unique and are not described by any single theory. For each new formulation, a specific development trajectory is required, and the versatility of lactose can be exploited to optimize each formulation. In this review, recent developments in lactose-based DPI formulations are discussed. The effects of varying the material properties of lactose carrier particles, such as particle size, shape, and morphology are reviewed. Owing to the complex interactions between the particles in a formulation, processing adhesive mixtures of lactose with the active ingredient is crucial. Therefore, blending and filling processes for DPI formulations are also reviewed. While the role of ternary agents, such as magnesium stearate, has increased, lactose remains the excipient of choice in carrier-based DPI formulations. Therefore, new developments in lactose-based DPI formulations are crucial in the optimization of inhalable medicine performance.

Pulmonary Delivery of Emerging Antibacterials for Bacterial Lung Infections Treatment

Bacterial infections in the respiratory tract are considered as one of the major challenges to the public health worldwide. Pulmonary delivery is an attractive approach in the management of bacterial respiratory infections with a few inhaled antibiotics approved. However, with the rapid emergence of antibiotic-resistant bacteria, it is necessary to develop new/alternative inhaled antibacterial agents in the post-antibiotic era. A pipeline of novel biological antibacterial agents, including antimicrobial peptides, RNAi therapeutics, and bacteriophages, has emerged to combat bacterial infections with excellent performance. In this review, the causal effects of bacterial infections on the related pulmonary infectious diseases will be firstly introduced. This is followed by an overview on the development of emerging antibacterial therapeutics for managing lung bacterial infections through nebulization/inhalation of dried powders. The obstacles and underlying proposals regarding their clinical transformation are also discussed to seek insights for further development. Research on inhaled therapy of these emerging antibacterials are still in the infancy, but the promising progress warrants further attention.

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 the Bacteriophage BUCT603 and Therapeutic Potential Evaluation Against Drug-Resistant Stenotrophomonas maltophilia in a Mouse Model

Stenotrophomonas maltophilia (S. maltophilia) is a common opportunistic pathogen that is resistant to many antibiotics. Bacteriophages are considered to be an effective alternative to antibiotics for the treatment of drug-resistant bacterial infections. In this study, we isolated and characterized a phage, BUCT603, infecting drug-resistant S. maltophilia. Genome sequencing showed BUCT603 genome was composed of 44,912 bp (32.5% G + C content) with 64 predicted open reading frames (ORFs), whereas no virulence-related genes, antibiotic-resistant genes or tRNA were identified. Whole-genome alignments showed BUCT603 shared 1% homology with other phages in the National Center for Biotechnology Information (NCBI) database, and a phylogenetic analysis indicated BUCT603 can be classified as a new member of the Siphoviridae family. Bacteriophage BUCT603 infected 10 of 15 S. maltophilia and used the TonB protein as an adsorption receptor. BUCT603 also inhibited the growth of the host bacterium within 1 h in vitro and effectively increased the survival rate of infected mice in a mouse model. These findings suggest that bacteriophage BUCT603 has potential for development as a candidate treatment of S. maltophilia 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.

PhageCocktail: An R package to design phage cocktails from experimental phage-bacteria infection networks

BACKGROUND AND OBJECTIVE

Phage therapy is a resurgent strategy used in medicine and the food industry to lyse bacteria that cause damage to health or spoil a food product. Frequently, phage-bacteria infection networks have a large size, making it impossible to manually study all possible phage cocktails. Thus, this article presents an R package called PhageCocktail to automatically design efficient phage cocktails from phage-bacteria infection networks.

METHODS

This R package includes four different methods for designing phage cocktails: ExhaustiveSearch, ExhaustivePhi, ClusteringSearch, and ClusteringPhi. These four methods are explained in detail and are evaluated using 13 empirical phage-bacteria infection networks. More specifically, runtime and expected success (fraction of lysed bacteria) are analyzed.

RESULTS

The four methods have variations in terms of runtime and quality of the results. ExhaustiveSearch always provides the best possible phage cocktail, but its runtime could be long. ExhaustivePhi only focuses on one cocktail size, the one estimated as the best; thus, its runtime is less than ExhaustiveSearch, but it can produce cocktails with more phages than necessary. ClusteringSearch and ClusteringPhi are very fast (generally, less than one millisecond), providing always immediate results due to clustering techniques, but their accuracies can be lower, yielding cocktails with lower expected successes.

CONCLUSIONS

The larger the phage-bacteria infection network is, the more complex its analysis is. Thus, this tool eases this task for scientists and other users while designing phage cocktails of good quality. This R package includes four different methods; therefore, users may choose among them, considering their preferences in speed and accuracy of results.

Preoptimized phage cocktail for use in aerosols against nosocomial transmission of carbapenem-resistant Acinetobacter baumannii: A 3-year prospective intervention study

Using bacteriophages (phages) as environmental sanitizers has been recognized as a potential alternative method to remove bacterial contamination in vitro; however, very few studies are available on the application of phages for infection control in hospitals. Here, we performed a 3-year prospective intervention study using aerosolized phage cocktails as biocontrol agents against carbapenem-resistant Acinetobacter baumannii (CRAB) infection in the hospital. When a CRAB-infected patient was identified in an intensive care unit (ICU), their surrounding environment was chosen for phage aerosol decontamination. Before decontamination, 501 clinical specimens from the patients were subjected to antibiotic resistance analysis and phage typing. The optimal phage cocktails were a combination of different phage families or were constructed by next-evolutionary phage typing with the highest score for the host lysis zone to prevent the development of environmental CRAB phage resistance. The phage infection percentage of the antibiotic-resistant A. baumannii strains was 97.1%, whereas the infection percentage in the antibiotic-susceptible strains was 79.3%. During the phage decontamination periods from 2017 to 2019, the percentage of carbapenem-resistant A. baumannii in test ICUs decreased significantly from 65.3% to 55%. The rate of new acquisitions of CRAB infection over the three years was 4.4 per 1000 patient-days, which was significantly lower than that in the control wards (8.9 per 1000 patient-days) where phage decontamination had never been performed. In conclusion, our results support the potential of phage cocktails to decrease CRAB infection rates, and the aerosol generation process may make this approach more comprehensive and time-saving.

Combating Infectious Diseases with Synthetic Biology

Over the past decades, there have been numerous outbreaks, including parasitic, fungal, bacterial, and viral infections, worldwide. The rate at which infectious diseases are emerging is disproportionate to the rate of development for new strategies that could combat them. Therefore, there is an increasing demand to develop novel, specific, sensitive, and effective methods for infectious disease diagnosis and treatment. Designed synthetic systems and devices are becoming powerful tools to treat human diseases. The advancement in synthetic biology offers efficient, accurate, and cost-effective platforms for detecting and preventing infectious diseases. Herein we focus on the latest state of living theranostics and its implications.

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.

Novel investigational treatments for ventilator-associated pneumonia and critically ill patients in the intensive care unit

INTRODUCTION

Ventilator-associated pneumonia (VAP) is common; its prevalence has been highlighted by the Covid-19 pandemic. Even young patients can suffer severe nosocomial infection and prolonged mechanical ventilation. Multidrug-resistant bacteria can spread alarmingly fast around the globe and new antimicrobials are struggling to keep pace; hence physicians must stay abreast of new developments in the treatment of nosocomial pneumonia and VAP.

AREAS COVERED

This narrative review examines novel antimicrobial investigational drugs and their implementation in the ICU setting for VAP. The paper highlights novel approaches such as monoclonal antibody treatments for P. aeruginosa and S. aureus, and phage antibiotic synthesis. The paper also examines mechanisms of resistance in gram-negative bacteria, virulence factors and inhaled antibiotics and questions what may be on the horizon in terms of emerging treatment strategies.

EXPERT OPINION

The post-antibiotic era is rapidly approaching and the need for personalised medicine, point-of-care microbial sensitivity testing and development of biomarkers for severe infections is clear. Results from emerging and new antibiotics are encouraging, but infection control measures and de-escalation protocols must be employed to prolong their usefulness in critical illness.

Advancements in Particle Engineering for Inhalation Delivery of Small Molecules and Biotherapeutics

Dry powder inhalation formulations have become increasingly popular for local and systemic delivery of small molecules and biotherapeutics. Powder formulations provide distinct advantages over liquid formulations such as elimination of cold chain due to room temperature stability, improved portability, and the potential for increasing patient adherence. To become a viable product, it is essential to develop formulations that are stable (physically, chemically and/or biologically) and inhalable over the shelf-life. Physical particulate properties such as particle size, morphology and density, as well as chemical properties can significantly impact aerosol performance of the powder. This review will cover these critical attributes that can be engineered to enhance the dispersibility of inhalation powder formulations. Challenges in particle engineering for biotherapeutics will be assessed, followed by formulation strategies for overcoming the hurdles. Finally, the review will discuss recent examples of successful dry powder biotherapeutic formulations for inhalation delivery that have been clinically assessed.

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.

β-lactam Resistance in Pseudomonas aeruginosa: Current Status, Future Prospects

Pseudomonas aeruginosa is a major opportunistic pathogen, causing a wide range of acute and chronic infections. β-lactam antibiotics including penicillins, carbapenems, monobactams, and cephalosporins play a key role in the treatment of P. aeruginosa infections. However, a significant number of isolates of these bacteria are resistant to β-lactams, complicating treatment of infections and leading to worse outcomes for patients. In this review, we summarize studies demonstrating the health and economic impacts associated with β-lactam-resistant P. aeruginosa. We then describe how β-lactams bind to and inhibit P. aeruginosa penicillin-binding proteins that are required for synthesis and remodelling of peptidoglycan. Resistance to β-lactams is multifactorial and can involve changes to a key target protein, penicillin-binding protein 3, that is essential for cell division; reduced uptake or increased efflux of β-lactams; degradation of β-lactam antibiotics by increased expression or altered substrate specificity of an AmpC β-lactamase, or by the acquisition of β-lactamases through horizontal gene transfer; and changes to biofilm formation and metabolism. The current understanding of these mechanisms is discussed. Lastly, important knowledge gaps are identified, and possible strategies for enhancing the effectiveness of β-lactam antibiotics in treating P. aeruginosa infections are considered.

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.