Bacteriophage encapsulation: Trends and potential applications

On the Infectivity of Bacteriophages in Polyelectrolyte Multilayer Films: Inhibition or Preservation of Their Bacteriolytic Activity?

Antibiotic resistance in bacterial cells has motivated the scientific community to design new and efficient (bio)materials with targeted bacteriostatic and/or bactericide properties. In this work, a series of polyelectrolyte multilayer films differing in terms of polycation-polyanion combinations are constructed according to the layer-by-layer deposition method. Their capacities to host T4 and φx174 phage particles and maintain their infectivity and bacteriolytic activity are thoroughly examined. It is found that the macroscopic physicochemical properties of the films, which includes film thickness, swelling ratio, or mechanical stiffness (as derived by atomic force microscopy and spectroscopy measurements), do not predominantly control the selectivity of the films for hosting infective phages. Instead, it is evidenced that the intimate electrostatic interactions locally operational between the loaded phages and the polycationic and polyanionic PEM components may lead to phage activity reduction and preservation/enhancement, respectively. It is argued that the underlying mechanism involves the screening of the phage capsid receptors (operational in cell recognition/infection processes) because of the formation of either polymer-phage hetero-assemblies or polymer coating surrounding the bioactive phage surface.

Bacterial Endospores as Phage Genome Carriers and Protective Shells

Bacterial endospores can serve as phage genome protection shells against various environmental stresses to enhance microbial control applications. The genomes of polyvalent lytic Bacillus phages PBSC1 and PBSC2, which infect both B. subtilis subsp. subtilis and B. cereus NRS 248, were incorporated into B. subtilis endospores (without integration into the host chromosome). When PBSC1 and PBSC2 were released from germinating endospores, they significantly inhibited the growth of the targeted opportunistic pathogen B. cereus Optimal endospore entrapment was achieved when phages were introduced to the fast-sporulating prespores at a multiplicity of infection of 1. Longer endospore maturation (48 h versus 24 h) increased both spore yield and efficiency of entrapment. Compared with free phages, spore-protected phage genomes showed significantly higher resistance toward high temperatures (60 to 80°C), extreme pH (pH 2 or pH 12), and copper ions (0.1 to 10 mg/liter). Endospore germination is inducible by low concentrations of l-alanine or by a germinant mixture (l-asparagine, d-glucose, d-fructose, and K+) to trigger the expression, assembly, and consequent release of phage particles within 60 to 90 min. Overall, the superior resiliency of polyvalent phages protected by endospores might enable nonrefrigerated phage storage and enhance phage applications after exposure to adverse environmental conditions.IMPORTANCE Bacteriophages are being considered for the control of multidrug-resistant and other problematic bacteria in environmental systems. However, the efficacy of phage-based microbial control is limited by infectivity loss during phage delivery and/or storage. Here, we exploit the pseudolysogenic state of phages, which involves incorporation of their genome into bacterial endospores (without integration into the host chromosome), to enhance survival in unfavorable environments. We isolated polyvalent (broad-host-range) phages that efficiently infect both benign and opportunistically pathogenic Bacillus strains and encapsulated the phage genomes in B. subtilis endospores to significantly improve resistance to various environmental stressors. Encapsulation by spores also significantly enhanced phage genome viability during storage. We also show that endospore germination can be induced on demand with nutrient germinants that trigger the release of active phages. Overall, we demonstrate that encapsulation of polyvalent phage genomes into benign endospores holds great promise for broadening the scope and efficacy of phage biocontrol.

Strategies to Encapsulate the Staphylococcus aureus Bacteriophage phiIPLA-RODI

The antimicrobial properties of bacteriophages make them suitable food biopreservatives. However, such applications require the development of strategies that ensure stability of the phage particles during food processing. In this study, we assess the protective effect of encapsulation of the Staphylococcus aureus bacteriophage phiIPLA-RODI in three kinds of nanovesicles (niosomes, liposomes, and transfersomes). All these systems allowed the successful encapsulation of phage phiIPLA-RODI with an efficiency ranged between 62% and 98%, regardless of the concentration of components (like phospholipids and surfactants) used for vesicle formation. Only niosomes containing 30 mg/mL of surfactants exhibited a slightly lower percentage of encapsulation. Regarding particle size distribution, the values determined for niosomes, liposomes, and transfersomes were 0.82 ± 0.09 µm, 1.66 ± 0.21 µm, and 0.55 ± 0.06 µm, respectively. Importantly, bacteriophage infectivity was maintained during storage for 6 months at 4 °C for all three types of nanovesicles, with the exception of liposomes containing a low concentration of components. In addition, we observed that niosomes partially protected the phage particles from low pH. Thus, while free phiIPLA-RODI was not detectable after 60 min of incubation at pH 4.5, titer of phage encapsulated in niosomes decreased only 2 log units. Overall, our results show that encapsulation represents an appropriate procedure to improve stability and, consequently, antimicrobial efficacy of phages for application in the food processing industry.

Nano/Micro Formulations for Bacteriophage Delivery

Encapsulation methodologies allow the protection of bacteriophages for overcoming critical environmental conditions. Moreover, they improve the stability and the controlled delivery of bacteriophages which is of great innovative value in bacteriophage therapy. Here, two different encapsulation methodologies of bacteriophages are described using two biocompatible materials: a lipid cationic mixture and a combination of alginate with the antacid CaCO₃. To perform bacteriophage encapsulation, a purified lysate highly concentrated (around 10¹⁰-10¹¹ pfu/mL) is necessary, and to dispose of a specific equipment. Both methodologies have been successfully applied for encapsulating Salmonella bacteriophages with different morphologies. Also, the material employed does not modify the antibacterial action of bacteriophages. Moreover, both technologies can also be adapted to any bacteriophage and possibly to any delivery route for bacteriophage therapy.

Microencapsulation of Clostridium difficile specific bacteriophages using microfluidic glass capillary devices for colon delivery using pH triggered release

The prevalence of pathogenic bacteria acquiring multidrug antibiotic resistance is a global health threat to mankind. This has motivated a renewed interest in developing alternatives to conventional antibiotics including bacteriophages (viruses) as therapeutic agents. The bacterium Clostridium difficile causes colon infection and is particularly difficult to treat with existing antibiotics; phage therapy may offer a viable alternative. The punitive environment within the gastrointestinal tract can inactivate orally delivered phages. C. difficile specific bacteriophage, myovirus CDKM9 was encapsulated in a pH responsive polymer (Eudragit® S100 with and without alginate) using a flow focussing glass microcapillary device. Highly monodispersed core-shell microparticles containing phages trapped within the particle core were produced by in situ polymer curing using 4-aminobenzoic acid dissolved in the oil phase. The size of the generated microparticles could be precisely controlled in the range 80 μm to 160 μm through design of the microfluidic device geometry and by varying flow rates of the dispersed and continuous phase. In contrast to free 'naked' phages, those encapsulated within the microparticles could withstand a 3 h exposure to simulated gastric fluid at pH 2 and then underwent a subsequent pH triggered burst release at pH 7. The significance of our research is in demonstrating that C. difficile specific phage can be formulated and encapsulated in highly uniform pH responsive microparticles using a microfluidic system. The microparticles were shown to afford significant protection to the encapsulated phage upon prolonged exposure to an acid solution mimicking the human stomach environment. Phage encapsulation and subsequent release kinetics revealed that the microparticles prepared using Eudragit® S100 formulations possess pH responsive characteristics with phage release triggered in an intestinal pH range suitable for therapeutic purposes. The results reported here provide proof-of-concept data supporting the suitability of our approach for colon targeted delivery of phages for therapeutic purposes.

Microencapsulation with alginate/CaCO3: A strategy for improved phage therapy

Bacteriophages are promising therapeutic agents that can be applied to different stages of the commercial food chain. In this sense, bacteriophages can be orally administered to farm animals to protect them against intestinal pathogens. However, the low pH of the stomach, the activities of bile and intestinal tract enzymes limit the efficacy of the phages. This study demonstrates the utility of an alginate/CaCO₃ encapsulation method suitable for bacteriophages with different morphologies and to yield encapsulation efficacies of ~100%. For the first time, a cocktail of three alginate/CaCO₃-encapsulated bacteriophages was administered as oral therapy to commercial broilers infected with Salmonella under farm-like conditions. Encapsulation protects the bacteriophages against their destruction by the gastric juice. Phage release from capsules incubated in simulated intestinal fluid was also demonstrated, whereas encapsulation ensured sufficient intestinal retention of the phages. Moreover, the small size of the capsules (125–150 μm) enables their use in oral therapy and other applications in phage therapy. This study evidenced that a cocktail of the three alginate/CaCO₃-encapsulated bacteriophages had a greater and more durable efficacy than a cocktail of the corresponding non-encapsulated phages in as therapy in broilers against Salmonella, one of the most common foodborne pathogen.

Developing and optimizing bacteriophage treatment to control enterohemorrhagic Escherichia coli on fresh produce

Bacteriophages are potentially useful in controlling foodborne pathogens on minimally processed products since phage application is a non-destructive treatment. The purpose of this study was to evaluate the efficacy of a newly isolated environmental bacteriophage against enterohemorrhagic Escherichia coli on fresh produce, and optimize the treatment with consideration for potential application. Seven anti E. coli O157:H7 EDL933 bacteriophages were isolated from various sources; the most promising was isolated from municipal wastewater. This isolate (designated as E. coli phage OSY-SP) was propagated with the host, in a growth medium, to a titer of 10(8) PFU/ml. Before inoculation into fresh produce, E. coli phage OSY-SP was incubated with the host bacterium, spent medium was filter-sterilized, and the resulting crude lysate was used as a source of phage inocula for preliminary experiments. For optimized testing, phage in the crude lysate was purified by ultra-centrifugation and resuspension in phosphate-buffered saline. Efficacy of phage treatments was determined as a function of fresh produce type (cut green pepper or spinach leaves), treatment time (2 or 5min rinsing), and temperature of holding treated produce (4°C, 25°, or a combination of both temperatures). Cut green pepper was treated with UV light, to eliminate background microbiota, then spot-inoculated with E. coli O157:H7 EDL933 on cut edges, and the inoculum was allowed to dry. Because of its susceptibility to damage, baby spinach leaves were not subjected to a decontamination treatment. These leaves were inoculated with the green fluorescent protein-labeled E. coli O157:H7 B6-914 to facilitate inoculum enumeration in the presence of background microbiota. Phage suspension was applied to the inoculated fresh produce that was subsequently held for three days under variable storage conditions. The optimized phage treatment decreased the populations of pathogenic E. coli by 2.4-3.0logCFU/g on cut green pepper (5-min rinse) and 3.4-3.5logCFU/g on spinach leaves (2-min rinse), during 72h storage. The majority of this decline was caused by the antimicrobial action of the phage. These findings suggest the utility of bacteriophage to selectively control pathogens on fresh produce.