Manufacturing and ambient stability of shelf freeze dried bacteriophage powder formulations

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.

Alginate- and Chitosan-Modified Gelatin Hydrogel Microbeads for Delivery of E. coli Phages

Bacterial infections are among the most significant health problems/concerns worldwide. A very critical concern is the rapidly increasing number of antibiotic-resistant bacteria, which requires much more effective countermeasures. As nature's antibacterial entities, bacteriophages shortly ("phages") are very important alternatives to antibiotics, having many superior features compared with antibiotics. The development of phage-carrying controlled-release formulations is still challenging due to the need to protect their activities in preparation, storage, and use, as well as the need to create more user-friendly forms by considering their application area/site/conditions. Here, we prepared gelatin hydrogel microbeads by a two-step process. Sodium alginate was included for modification within the initial recipes, and these composite microbeads were further coated with chitosan. Their swelling ratio, average diameters, and Zeta potentials were determined, and degradations in HCl were demonstrated. The target bacteria Escherichia coli (E.coli) and its specific phage (T4) were obtained from bacterial culture collections and propagated. Phages were loaded within the microbeads with a simple method. The phage release characteristics were investigated comparatively and were demonstrated here. High release rates were observed from the gelatin microbeads. It was possible to reduce the phage release rate using sodium alginate in the recipe and chitosan coating. Using these gelatin-based microbeads as phage carrier matrices-especially in lyophilized forms-significantly improved the phage stability even at room temperature. It was concluded that phage release from gelatin hydrogel microbeads could be further controlled by alginate and chitosan modifications and that user-friendly lyophilized phage formulations with a much longer shelf life could be produced.

Freeze-Drying of Encapsulated Bacteriophage T4 to Obtain Shelf-Stable Dry Preparations for Oral Application

Therapeutic application of bacterial viruses (phage therapy) has in recent years been rediscovered by many scientists, as a method which may potentially replace conventional antibacterial strategies. However, one of the main problems related to phage application is the stability of bacterial viruses. Though many techniques have been used to sustain phage activity, novel tools are needed to allow long-term phage storage and application in versatile forms. In this study, we combined two well-known methods for bacteriophage immobilization. First, encapsulated phages were obtained by means of extrusion-ionic gelation, and then alginate microspheres were dried using the lyophilization process (freeze-drying). To overcome the risk of phage instability upon dehydration, the microspheres were prepared with the addition of 0.3 M mannitol. Bacteriophage-loaded microspheres were stored at room temperature for 30 days and subsequently exposed to simulated gastric fluid (SGF). The survival of encapsulated phages after drying was significantly higher in the presence of mannitol. The highest number of viable bacteriophages exceeding 4.8 log10 pfu/mL in SGF were recovered from encapsulated and freeze-dried microspheres, while phages in lyophilized lysate were completely inactivated. Although the method requires optimization, it may be a promising approach for the immobilization of bacteriophages in terms of practical application.

Advanced Manufacturing, Formulation and Microencapsulation of Therapeutic Phages

Manufacturing and formulation of stable, high purity, and high dose bacteriophage drug products (DPs) suitable for clinical usage would benefit from improved process monitoring and control of critical process parameters that affect product quality attributes. Chemistry, Manufacturing, and Controls (CMC) for both upstream (USP) and downstream processes (DSP) need mapping of critical process parameters (CPP) and linking these to critical quality attributes (CQA) to ensure quality and consistency of phage drug substance (DS) and DPs development. Single-use technologies are increasingly becoming the go-to manufacturing option with benefits both for phage bioprocess development at the engineering run research stage and for final manufacture of the phage DS. Future phage DPs under clinical development will benefit from implementation of process analytical technologies (PAT) for better process monitoring and control. These are increasingly being used to improve process robustness (to reduce batch-to-batch variability) and productivity (yielding high phage titers). Precise delivery of stable phage DPs that are suitably formulated as liquids, gels, solid-oral dosage forms, and so forth, could significantly enhance efficacy of phage therapy outcomes. Pre-clinical development of phage DPs must include at an early stage of development, considerations for their formulation including their characterization of physiochemical properties (size, charge, etc.), buffer pH and osmolality, compatibility with regulatory approved excipients, storage stability (packaging, temperature, humidity, etc.), ease of application, patient compliance, ease of manufacturability using scalable manufacturing unit operations, cost, and regulatory requirements.

Use of Trehalose as an Additive to Bacteriophage Vb_Pd_PDCC-1: Long-Term Preservation Analysis and Its Biocontrol Against Vibrio diabolicus Infection

Phage therapy is a promising alternative to control bacterial diseases and the increasing problem of antibiotic resistance. In this sense, this research evaluates the viability of lyophilized vibrio phage vB_Pd_PDCC-1 using trehalose as a preservative excipient at different concentrations (4, 2, 1, and 0.5% w/v) and its potential for phage therapy application against a pathogenic bacteria Vibrio diabolicus in brine shrimp nauplii (Artemia franciscana). The lyophilized phages were stored at 4 and 23 °C and rehydrated using biological sterile saline solution to test their viability at days 1, 15, and 60 post-lyophilization. The results showed that trehalose is beneficial in maintaining the viability of post-lyophilization phages (without titer losses) at 4 °C and even at room temperature (23 °C). When lyophilized phages with 4% w/v trehalose concentration were stored at 23 °C, they had not titer losses among the trials; viability and titer concentration were maintained up to 60 days at log 7. The use of lyophilized phage PDCC-1 increased brine shrimp survival and reduced Vibrio concentrations. The present study has identified trehalose as a promising lyophilization excipient to effectively preserve lyophilized bacteriophages for biotechnological applications and long-term storage.

Using bugs as drugs: administration of bacteria-related microbes to fight cancer

Driven by the advancement of microbiology and cancer biology, bioengineering of bacteria-related microbes has demonstrated great potential in targeted cancer therapy. Presently, the major administration routes of bacteria-related microbes for cancer treatment include intravenous injection, intratumoral injection, intraperitoneal injection, and oral delivery. Administration routes of bacteria play a key role in anticancer therapeutic efficacy since different delivery approaches might exert an anticancer effect through diverse mechanisms. Herein, we provide an overview of the primary routes of bacteria administration as well as their advantages and limitations. Furthermore, we discuss that microencapsulation can overcome the current challenges of direct administration of free bacteria. We also review the latest advancements in combining functional particles with engineered bacteria to fight against cancer, which can be further coupled with conventional anticancer therapies to improve the therapeutic effect. Eventually, we highlight the application prospect of bioprinting in cancer bacteriotherapy, which enables the long-term sustained delivery and individualized dose regimen, representing a new paradigm for personalized cancer treatment.

Encapsulation and delivery of phage as a novel method for gut flora manipulation in situ: A review

Intestinal flora regulation is an effective method to intervene and treat diseases associated with microbiome imbalance. In addition to conventional probiotic supplement, phage delivery has recently exhibited great prospect in modifying gut flora composition and regulating certain gene expression of gut bacteria. However, the protein structure of phage is vulnerable to external factors during storage and delivery, which leads to the loss of infection ability and flora regulation function. Encapsulation strategy provides an effective solution for improving phage stability and precisely controlling delivery dosage. Different functional materials including enzyme-responsive and pH-responsive polymers have been used to construct encapsulation carriers to protect phages from harsh conditions and release them in the colon. Meanwhile, diverse carriers showed different characteristics in structure and function, which influenced their protective effect and delivery efficiency. This review systematically summarizes recent research progress on the phage encapsulation and delivery, with an emphasis on function properties of carrier systems in the protection effect and colon-targeted delivery. The present review may provide a theoretical reference for the encapsulation and delivery of phage as microbiota modulator, so as to expedite the development of functional material and delivery carrier, as well as the advances in practical application of intestinal flora regulation.

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.

Viability, Stability and Biocontrol Activity in Planta of Specific Ralstonia solanacearum Bacteriophages after Their Conservation Prior to Commercialization and Use

Ralstonia solanacearum is a pathogen that causes bacterial wilt producing severe damage in staple solanaceous crops. Traditional control has low efficacy and/or environmental impact. Recently, the bases of a new biotechnological method by lytic bacteriophages vRsoP-WF2, vRsoP-WM2 and vRsoP-WR2 with specific activity against R. solanacearum were established. However, some aspects remain unknown, such as the survival and maintenance of the lytic activity after submission to a preservation method as the lyophilization. To this end, viability and stability of lyophilized vRsoP-WF2, vRsoP-WM2 and vRsoP-WR2 and their capacity for bacterial wilt biocontrol have been determined against one pathogenic Spanish reference strain of R. solanacearum in susceptible tomato plants in different conditions and making use of various cryoprotectants. The assays carried out have shown satisfactory results with respect to the viability and stability of the bacteriophages after the lyophilization process, maintaining high titers throughout the experimental period, and with respect to the capacity of the bacteriophages for the biological control of bacterial wilt, controlling this disease in more than 50% of the plants. The results offer good prospects for the use of lyophilization as a conservation method for the lytic bacteriophages of R. solanacearum in view of their commercialization as biocontrol agents.

Deploying Viruses against Phytobacteria: Potential Use of Phage Cocktails as a Multifaceted Approach to Combat Resistant Bacterial Plant Pathogens

Plants in nature are under the persistent intimidation of severe microbial diseases, threatening a sustainable food production system. Plant-bacterial pathogens are a major concern in the contemporary era, resulting in reduced plant growth and productivity. Plant antibiotics and chemical-based bactericides have been extensively used to evade plant bacterial diseases. To counteract this pressure, bacteria have evolved an array of resistance mechanisms, including innate and adaptive immune systems. The emergence of resistant bacteria and detrimental consequences of antimicrobial compounds on the environment and human health, accentuates the development of an alternative disease evacuation strategy. The phage cocktail therapy is a multidimensional approach effectively employed for the biocontrol of diverse resistant bacterial infections without affecting the fauna and flora. Phages engage a diverse set of counter defense strategies to undermine wide-ranging anti-phage defense mechanisms of bacterial pathogens. Microbial ecology, evolution, and dynamics of the interactions between phage and plant-bacterial pathogens lead to the engineering of robust phage cocktail therapeutics for the mitigation of devastating phytobacterial diseases. In this review, we highlight the concrete and fundamental determinants in the development and application of phage cocktails and their underlying mechanism, combating resistant plant-bacterial pathogens. Additionally, we provide recent advances in the use of phage cocktail therapy against phytobacteria for the biocontrol of devastating plant diseases.

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.

Manufacturing Stable Bacteriophage Powders by Including Buffer System in Formulations and Using Thin Film Freeze-drying Technology

PURPOSE

Bacteriophage (phage) therapy has re-gained attention lately given the ever-increasing prevalence of multi-drug resistance 'super-bugs'. To develop therapeutic phage into clinically usable drug products, the strategy of solidifying phage formulations has been implemented to diversify the dosage forms and to overcome the storage condition limitations for liquid phage formulations.

METHOD

In our work, we hypothesize and tested that an advanced technology, thin film freeze-drying (TFFD), can be used to produce phage containing dry powders without significantly losing phage viability. Here we selected T7 phage as our model phage in a preliminary screening study.

RESULTS

We found that a binary excipient matrix of sucrose and leucine at ratios of 90:10 or 75:25 by weight, protected phage from the stresses encountered during the TFFD process. In addition, we confirmed that incorporating a buffer system in the formulation significantly improved the survival of phage during the initial freezing step and subsequent sublimation step in the solidifying processes. The titer loss of phage in SM buffer (Tris/NaCl/MgSO4) containing formulation was as low as 0.19 log plaque forming units, which indicated that phage function was well preserved after the TFFD process. The presence of buffers markedly reduced the geometric particle sizes as determined by a dry dispersion method using laser diffraction, which indicated that the TFFD phage powder formulations were easily sheared into smaller powder aggregates, an ideal property for facilitating a variety of topical drug delivery routes including pulmonary delivery through dry powder inhalers, nebulization after reconstitution, and intranasal or wound therapy, etc. CONCLUSION: From these findings, we show that introducing buffer system can stabilize phage during dehydration processes, and TFFD, as a novel particle engineering method, can successfully produce phage containing powders that possess the desired properties for bioactivity and potentially for inhalation therapy.

The Influence of Formulation Components and Environmental Humidity on Spray-Dried Phage Powders for Treatment of Respiratory Infections Caused by Acinetobacter baumannii

The feasibility of using respirable bacteriophage (phage) powder to treat lung infections has been demonstrated in animal models and clinical studies. This work investigated the influence of formulation compositions and excipient concentrations on the aerosol performance and storage stability of phage powder. An anti-Acinetobacter baumannii phage vB_AbaM-IME-AB406 was incorporated into dry powders consisting of trehalose, mannitol and L-leucine for the first time. The phage stability upon the spray-drying process, room temperature storage and powder dispersion under different humidity conditions were assessed. In general, powders prepared with higher mannitol content (40% of the total solids) showed a lower degree of particle merging and no sense of stickiness during sample handling. These formulations also provided better storage stability of phage with no further titer loss after 1 month and <1 log titer loss in 6 months at high excipient concentration. Mannitol improved the dispersibility of phage powders, but the in vitro lung dose dropped sharply after exposure to high-humidity condition (65% RH) for formulations with 20% mannitol. While previously collected knowledge on phage powder preparation could be largely extended to formulate A. baumannii phage into inhalable dry powders, the environmental humidity may have great impacts on the stability and dispersion of phage; therefore, specific attention is required when optimizing phage powder formulations for global distribution.

Formulations for Bacteriophage Therapy and the Potential Uses of Immobilization

The emergence of antibiotic-resistant pathogens is becoming increasingly problematic in the treatment of bacterial diseases. This has led to bacteriophages receiving increased attention as an alternative form of treatment. Phages are effective at targeting and killing bacterial strains of interest and have yielded encouraging results when administered as part of a tailored treatment to severely ill patients as a last resort. Despite this, success in clinical trials has not always been as forthcoming, with several high-profile trials failing to demonstrate the efficacy of phage preparations in curing diseases of interest. Whilst this may be in part due to reasons surrounding poor phage selection and a lack of understanding of the underlying disease, there is growing consensus that future success in clinical trials will depend on effective delivery of phage therapeutics to the area of infection. This can be achieved using bacteriophage formulations instead of purely liquid preparations. Several encapsulation-based strategies can be applied to produce phage formulations and encouraging results have been observed with respect to efficacy as well as long term phage stability. Immobilization-based approaches have generally been neglected for the production of phage therapeutics but could also offer a viable alternative.

A Hundred Years of Bacteriophages: Can Phages Replace Antibiotics in Agriculture and Aquaculture?

Agriculture, together with aquaculture, supplies most of the foodstuffs required by the world human population to survive. Hence, bacterial diseases affecting either agricultural crops, fish, or shellfish not only cause large economic losses to producers but can even create food shortages, resulting in malnutrition, or even famine, in vulnerable populations. Years of antibiotic use in the prevention and the treatment of these infections have greatly contributed to the emergence and the proliferation of multidrug-resistant bacteria. This review addresses the urgent need for alternative strategies for the use of antibiotics, focusing on the use of bacteriophages (phages) as biocontrol agents. Phages are viruses that specifically infect bacteria; they are highly host-specific and represent an environmentally-friendly alternative to antibiotics to control and kill pathogenic bacteria. The information evaluated here highlights the effectiveness of phages in the control of numerous major pathogens that affect both agriculture and aquaculture, with special emphasis on scientific and technological aspects still requiring further development to establish phagotherapy as a real universal alternative to antibiotic treatment.

Effects of lyophilization on the stability of bacteriophages against different serogroups of Shiga toxin-producing Escherichia coli

Lyophilization is commonly used to effectively preserve the stability of bacteriophages (phages) in long-term storage. However, information regarding the lyophilization of phages specific to Shiga toxin-producing Escherichia coli (STEC) strains is scarce. The objective of this study was to determine the effects of lyophilization with different cryoprotectants (sucrose and trehalose) and concentrations (0.1 M and 0.5 M) on the stability of seven lytic phages specific to STEC O157 and top 6 non-O157 strains during 6-month storage at -80 °C. The titers of lyophilized phages specific to STEC O26 (S1 O26) and STEC O121 (Pr121lvw) did not exhibit significant reduction after 6-month storage regardless of the use of cryoprotectants. Phages lytic against STEC O103 (Ro103C3lw) and STEC O145 (Ro145clw) with 0.1 M sucrose retained similar titers after lyophilization and frozen storage for 6 months (P > 0.05). Despite subtle differences, these results indicated that most of the selected phages had similar titer retention with the same cryoprotectants. Additionally, lytic activities of the phages against their primary hosts were not affected after lyophilization and 6-month frozen storage. Moreover, no detectable damage was observed on the lyophilized phage structures. These findings provide valuable insight into the use of lyophilization to preserve phages lytic against STEC strains.

Inhalable bacteriophage powders: Glass transition temperature and bioactivity stabilization

Recent heightened interest in inhaled bacteriophage (phage) therapy for combating antibacterial resistance in pulmonary infections has led to the development of phage powder formulations. Although phages have been successfully bioengineered into inhalable powders with preserved bioactivity, the stabilization mechanism is yet unknown. This paper reports the first study investigating the stabilization mechanism for phages in these powders. Proteins and other biologics are known to be preserved in dry state within a glassy sugar matrix at storage temperatures (T s) at least ~50°C below the glass transition temperature (T g). This is because at (T g - T s) >50°C, molecules are sufficiently immobilized with reduced reactivity. We hypothesized that this glass stabilization mechanism may also be applicable to phages comprising mostly of proteins. In this study, spray dried powders of Pseudomonas phage PEV20 containing lactose and leucine as excipients were stored at 5, 25 or 50°C and 15 or 33% relative humidity (RH), followed by assessment of bioactivity (PEV20 stability) and physical properties. PEV20 was stable with negligible titer loss after storage at 5°C/15% RH for 250 days, while storage at 33% RH caused increased titer losses of 1 log10 and 3 log10 at 5 and 25°C, respectively. The plasticizing effect of water at 33% RH lowered the T g by 30°C, thus narrowing the gap between T s and T g to 19-28°C, which was insufficient for glass stabilization. In contrast, the (T g - T s) values were higher (range, 46-65°C) under the drier condition of 15% RH, resulting in the improved stability which corroborated with the vitrification hypothesis. Furthermore, phage remained stable (≤1 log10) when the (T g - T s) value lay between 26-48°C, but became inactivated as the value fell below 20°C. In conclusion, this study demonstrated that phage can be sufficiently stabilized in spray dried powders by keeping the (T g - T s) value above 46°C, thus supporting the vitrification hypothesis that phages are stabilized by immobilization inside a rigid glassy sugar matrix. These findings provide a guide to better manufacture and storage practices of inhaled phage powder products using for translational medicines.

Application of Adaptive Evolution to Improve the Stability of Bacteriophages during Storage

Phage stability is important for the successful application of bacteriophages as alternative antibacterial agents. Considering that temperature is a critical factor in phage stability, this study aimed to explore the possibility of improving long-term phage stability through adaptive evolution to elevated temperature. Evolution of three wild-type ancestral phages (Myoviridae phage Wc4 and Podoviridae phages CX5 and P-PSG-11) was induced by subjecting the phages to heat treatment at 60 °C for five cycles. The adapted phages showed better stability than the wild-type ancestral phages when subjected to heat treatment at 60 °C for 1 h and after 60 days of storage at 37 °C. However, the adapted phages could not withstand thermal treatment at 70 °C for 1 h. The infectivity and the lytic properties of the phages were not changed by the evolution process. Whole-genome sequencing revealed that single substitutions in the tail tubular proteins were the only changes observed in the genomes of the adapted phages. This study demonstrates that adaptive evolution could be used as a general method for enhancing the thermal stability of phages without affecting their lytic activity. Sequencing results showed that bacteriophages may exist as a population with minor heterogeneous mutants, which might be important to understand the ecology of phages in different environments.

Improved lyophilization conditions for long-term storage of bacteriophages

Phage therapy is one of the promising alternatives to combat the increasing problem of antibiotic resistance. Lyophilization is used for the preparation of pharmaceutical products to improve their stability in long-term storage. The aim of this study was to improve the stability of lyophilized bacteriophages using different excipients. Three lytic bacteriophages Escherichia phage ECP311, Klebsiella phage KPP235 and Enterobacter phage ELP140 were subjected to lyophilization using six different excipients: glucose, sucrose, gelatin, mannitol, polyethylene glycol and sorbitol. The lyophilized phages were stored at 4 °C and 37 °C and rehydrated using biological saline to test their viability at 5 months interval up to 20 months. The results showed that the use of sucrose, gelatin and their combination was beneficial in maintaining the viability of phages post-lyophilization. When lyophilized phages were stored at 4 °C, their viability was maintained up to 20 months, but at 37 °C there was a reduction in activity after 10 months. This is one of the few studies to report the lyophilization of phage cocktails to have viability for up to 10 months. Our study identified promising lyophilization excipients to effectively lyophilize bacteriophages for pharmaceutical applications and long-term storage.

Arming Filamentous Bacteriophage, a Nature-Made Nanoparticle, for New Vaccine and Immunotherapeutic Strategies

The pharmaceutical use of bacteriophages as safe and inexpensive therapeutic tools is collecting renewed interest. The use of lytic phages to fight antibiotic-resistant bacterial strains is pursued in academic and industrial projects and is the object of several clinical trials. On the other hand, filamentous bacteriophages used for the phage display technology can also have diagnostic and therapeutic applications. Filamentous bacteriophages are nature-made nanoparticles useful for their size, the capability to enter blood vessels, and the capacity of high-density antigen expression. In the last decades, our laboratory focused its efforts in the study of antigen delivery strategies based on the filamentous bacteriophage 'fd', able to trigger all arms of the immune response, with particular emphasis on the ability of the MHC class I restricted antigenic determinants displayed on phages to induce strong and protective cytotoxic responses. We showed that fd bacteriophages, engineered to target mouse dendritic cells (DCs), activate innate and adaptive responses without the need of exogenous adjuvants, and more recently, we described the display of immunologically active lipids. In this review, we will provide an overview of the reported applications of the bacteriophage carriers and describe the advantages of exploiting this technology for delivery strategies.

Implications of Bacteriophage- and Bacteriophage Component-Based Therapies for the Clinical Microbiology Laboratory

Treatment of bacterial infections is increasingly challenged by resistance to currently available antibacterial agents. Not only are such agents less likely to be active today than they were in the past, but their very use has selected for and continues to select for further resistance. Additional strategies for the management of bacterial illnesses must be identified. In this review, bacteriophage-based therapies are presented as one promising approach. In anticipation of their potential expansion into clinical medicine, clinical microbiologists may wish to acquaint themselves with bacteriophages and their antibacterial components and, specifically, with methods for testing them. Here, we reviewed the literature spanning January 2007 to March 2019 on bacteriophage and phage-encoded protein therapies of relevance to clinical microbiology.

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

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

Biocontrol of phytobacteria with bacteriophage cocktails

Crop loss due to plant pathogens has provoked renewed interest in bacteriophages as a feasible biocontrol strategy of plant diseases. Phage cocktails in particular present a viable option for broadening the phage host range, limiting the emergence of bacterial resistance while maintaining the lytic activity of the phages. It is therefore important that the design used to formulate a phage cocktail should result in the most effective cocktail against the pathogen. It is also critical that certain factors are considered during the formulation and application of a phage cocktail: their stability, the production time and cost of complex cocktails, the potential impact on untargeted bacteria, the timing of phage application, and the persistence in the plant environment. Continuous monitoring is required to ensure that the efficacy of a cocktail is sustained due to the dynamic nature of phages. Although phage cocktails are considered as a plausible biocontrol strategy of phytobacteria, more research needs to be done to understand the complex interaction between phages and bacteria in the plant environment, and to overcome the technical obstacles. © 2019 Society of Chemical Industry.

Atmospheric Spray Freeze Drying of Sugar Solution With Phage D29

Therapeutic bacteriophages offer a potential alternative approach in the treatment of drug resistant bacteria. In the present study, we examine the ability of atmospheric spray freeze-drying (ASFD) to process bacteriophage D29 into a solid dry formulation. Bacteriophage D29 is of particular interest due to its ability to infect Mycobacterium tuberculosis. A sugar solution containing bacteriophage D29 was sprayed and instantly frozen in a cold chamber. Cold drying gas was then passed through the chamber at a high flow rate and atmospheric pressure. Convective transport combined with the low temperature of the drying gas results in sublimation of ice, yielding a free-flowing, porous powder. The bacteriophages were atmospheric spray freeze-dried in solutions with varying concentrations of trehalose and mannitol. A solution of trehalose and mannitol at a mass ratio of 7:3 and a total mass concentration of 100 mg/mL led to powder with 4.9 ± 0.1% moisture content and an acceptable titer reduction of ∼0.6 logs. In comparison, a pure trehalose solution and a 1:1 ratio of trehalose and mannitol both had titer reductions of >1.5 logs. Spectroscopic analysis showed that trehalose in the powder was amorphous while mannitol completely crystallized during the drying process, both of which are desirable for preserving phage viability and storage in powders. The results highlight the potential for using ASFD as an alternative process in preserving biopharmaceutical products.