Phage Strains Research Articles

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

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

Composition of Bacteriophages for Therapeutic and Prophylactic Use in Monkeys

Keeping rhesus monkeys as laboratory animals requires timely prevention and treatment of infections, including diseases of bacterial etiology. Based on our own studies of the microflora of healthy and sick monkeys, as well as analysis of published reports, we identified clinically significant representatives of pathogenic and opportunistic bacteria: E. coli, Staphylococcus aureus, Klebsiella spp., Proteus spp. The isolates of these bacterial species and genera circulating in monkeys kept in the enclosure were isolated, four virulent bacteriophage strains with a wide spectrum of lytic activity against these isolates were selected and newly isolated. The composition based on virulent bacteriophage strains was tested on monkeys with assessment of its safety and its dynamics of detection of phage-specific DNA.

A lytic bacteriophage isolate reduced Clostridium perfringens induced lesions in necrotic enteritis challenged broilers.

Bacteriophages are viral predators of bacteria and are common in nature. Their host-specific infections against specific bacteria make them an attractive natural agent to control bacterial pathogens. Interest in the potential of bacteriophages as antibacterial agents in the production animal industries has increased. A total of 18 bacteriophages were isolated from Australian commercial poultry environments, from which three highly active phages were chosen for enrichment. Sequencing libraries were prepared using a Nextera XT kit (Illumina) and sequenced on an Illumina MiSeq instrument using 2 × 300 bp paired-end chemistry. The sequence data were then assembled and aligned with a2 bacteriophage as the reference. An animal trial was performed by oral gavaging Clostridium perfringens netB containing strain EHE-NE18 to the Ross 308 broiler chickens prior inoculation with Eimeria species. The chickens were raised following the management guide for Ross 308 from d 0 to d 21 and fed with starter and grower diets met the specific breed nutrient requirements. Body weight gain and feed intake were measured on d 9 and d 21 and FCR adjusted with mortality was calculated. The isolated bacteriophages only had only 96.7% similarity to the most closely related, previously characterized, Clostridium bacteriophage indicated that they might represent a novel strain of bacteriophage. A "cocktail" containing the three bacteriophages was capable of lysing four known disease-inducing C. perfringens strains in vitro. Oral administration of the bacteriophages cocktail to broilers challenged with necrotic enteritis markedly alleviated intestinal necrotic lesions in the duodenum and jejunum on day 16 post-hatch. The phage treatment significantly reduced the lesion scores of birds challenged with NE (P < 0.01), and the lesion scores between birds treated with the bacteriophages and the unchallenged birds were not statistically different (P > 0.05). However, no effect on the growth performance was observed during the recorded period of days 9-21. These findings suggest that bacteriophage treatment is a promising approach to protect intestinal health from C. perfringens induced necrotic enteritis. Further research will be required on the dosing, route of administration, and large scale validation studies to further advance this approach to pathogen control.

Implications of oral streptococcal bacteriophages in autism spectrum disorder

Growing evidence suggests altered oral and gut microbiota in autism spectrum disorder (ASD), but little is known about the alterations and roles of phages, especially within the oral microbiota in ASD subjects. We enrolled ASD (n = 26) and neurotypical subjects (n = 26) with their oral hygiene controlled, and the metagenomes of both oral and fecal samples (n = 104) are shotgun-sequenced and compared. We observe extensive and diverse oral phageome comparable to that of the gut, and clear signals of mouth-to-gut phage strain transfer within individuals. However, the overall phageomes of the two sites are widely different and show even less similarity in the oral communities between ASD and control subjects. The ASD oral phageome exhibits significantly reduced abundance and alpha diversity, but the Streptococcal phages there are atypically enriched, often dominating the community. The over-representation of Streptococcal phages is accompanied by enriched oral Streptococcal virulence factors and Streptococcus bacteria, all exhibiting a positive correlation with the severity of ASD clinical manifestations. These changes are not observed in the parallel sampling of the gut flora, suggesting a previously unknown oral-specific association between the excessive Streptococcal phage enrichment and ASD pathogenesis. The findings provide new evidence for the independent microbiome-mouth-brain connection, deepen our understanding of how the growth dynamics of bacteriophages and oral microbiota contribute to ASD, and point to novel effective therapeutics.

ISOLATION AND CHARACTERISTICS OF BACTERIOPHAGES SANITARY-INDICATIVE MICROORGANISMS

Isolated phages showed activity toward opportunistic and pathogenic bacteria of genera Escherichia (K3P1, K3P2, BIM BV-44 D) and Pseudomonas (PsP1), formed lysis zones shaped as negative homogeneous colonies with a clear-cut even edge (K3P1, PsP1, BIM BV -44 D), or negative colonies with a peripheral zone of partial lysis (K3P2). The diameter of phage plaques varied from 0,5–1,5 mm. Lytic activity spectrum of phage isolates was investigated. It was found that the studied bacteriophages displayed species specificity. Bacteriophages K3P1, K3P2 were distinguished by the highest lytic range. Differences in the isolated bacteriophages according to restriction profiles were revealed. Bacteriophage distinctions in restriction profiles were revealed. Interaction of bacteriophages with cells of bacteria of E. coli and Ps. aeruginosa was explored. The tested bacteriophage strains demonstrating lytic activity toward sanitary-indicative bacterial species may find use as disinfectants in detergents.

Ultrafast and Multiplexed Bacteriophage Susceptibility Testing by Surface Plasmon Resonance and Phase Imaging of Immobilized Phage Microarrays

In the context of bacteriophage (phage) therapy, there is an urgent need for a method permitting multiplexed, parallel phage susceptibility testing (PST) prior to the formulation of personalized phage cocktails for administration to patients suffering from antimicrobial-resistant bacterial infections. Methods based on surface plasmon resonance imaging (SPRi) and phase imaging were demonstrated as candidates for very rapid (&lt;2 h) PST in the broth phase. Biosensing layers composed of arrays of phages 44AHJD, P68, and gh-1 were covalently immobilized on the surface of an SPRi prism and exposed to liquid culture of either Pseudomonas putida or methicillin-resistant Staphylococcus aureus (i.e., either the phages’ host or non-host bacteria). Monitoring of reflectivity reveals susceptibility of the challenge bacteria to the immobilized phage strains. Investigation of phase imaging of lytic replication of gh-1 demonstrates PST at the single-cell scale, without requiring phage immobilization. SPRi sensorgrams show that on-target regions increase in reflectivity more slowly, stabilizing later and to a lower level compared to off-target regions. Phage susceptibility can be revealed in as little as 30 min in both the SPRi and phase imaging methods.

Combating antimicrobial resistance: an evidence-based overview of bacteriophage therapy.

Antimicrobial resistance (AMR) problems cause an enormous challenge to our world in medicine and in agriculture and many other fields. The current situation makes bacteriophage therapy an attractive therapeutic candidate. Nevertheless, very limited clinical trials on bacteriophage therapy were performed and completed as of presence. Bacteriophage therapy alludes to infecting bacteria with a virus, this often results in a bactericidal effect. The compiled studies support the feasibility of treating AMR with bacteriophage. However, the efficacy of specific bacteriophage strains and the accurate dosage have to be further studied and tested rigorously.

The importance of ecological dynamics in evolutionary processes: A host-bacteriophage model revisited

A recent study of adaptive dynamics of lysis propensity in temperate phages suggested that full lysogeny emerges as the outcome of bacteriophage evolution in a simple host-phage system. The conclusion is based on the premise that mutant strains necessarily appear in equilibrium host-phage environments. Revisiting the model, we show that the ecological system exhibits richer asymptotic dynamics and that, in a certain parameter regime, evolution may in fact drive lysis propensity towards an evolutionary singularity in which a non-zero proportion of phages initiate infection in a lytic cycle. These singularities act as points of evolutionary diversification, leading to periodic coexistence of two distinct phage strains on the evolutionary time-scale. One of the two strains in the dimorphic evolutionary singularity is fully lysogenic (in the sense that cell infection always leads to lysogeny), while the other is partially lytic. Our study thus highlights the importance of ecological interactions as a driver of evolution.

Assessment of Staphylococcal Clinical Isolates from Periprosthetic Joint Infections for Potential Bacteriophage Therapy.

Bacteriophage therapy is a potential adjunctive treatment for periprosthetic joint infections (PJIs) given the capabilities of bacteriophages to degrade biofilms, self-replicate, and lyse bacteria. However, many aspects of this therapeutic are ill-defined, and the narrow spectrum of bacteriophage activity along with limited available bacteriophage strains curb potential use for specific bacteria such as Staphylococcus aureus at the present time. Therefore, the aim of this study was to determine the feasibility of using bacteriophages for PJI by (1) categorizing the causative organisms in hip and knee PJI at a tertiary academic center and (2) evaluating in vitro activity of a group of bacteriophages against clinical S. aureus PJI isolates. Patients with chronic hip or knee PJI after undergoing the first stage of a 2-stage revision protocol from 2017 to 2020 were identified retrospectively by a query of the hospital billing database. The causative pathogens in 129 cases were reviewed and categorized. From this cohort, preserved S. aureus isolates were tested against a library of 15 staphylococcal bacteriophages to evaluate for bacterial growth inhibition over 48 hours. S. aureus was the most common pathogen causing PJI (26% [33] of 129 cases). Of 29 S. aureus samples that were analyzed for bacteriophage activity, 97% showed adequate growth inhibition of the predominant planktonic colonies by at least 1 bacteriophage strain. However, 24% of the 29 samples demonstrated additional smaller, slower-growing S. aureus colonies, none of which had adequate growth inhibition by any of the initial 14 bacteriophages. Of 5 secondary colonies that underwent subsequent testing with another bacteriophage with enhanced biofilm activity, 4 showed adequate growth inhibition. Effective bacteriophage therapeutics are potentially available for S. aureus PJI isolates. The differences in bacteriophage activity against the presumed small-colony variants compared with the planktonic isolates have important clinical implications. This finding suggests that bacteriophage attachment receptors differ between the different bacterial morphologic states, and supports future in vitro testing of bacteriophage therapeutics against both planktonic and stationary states of PJI clinical isolates to ensure activity.

Isolation, Characterization and Draft Genome Analysis of Bacteriophages Infecting Acidovorax citrulli.

Bacterial fruit blotch and seedling blight, caused by Acidovorax citrulli, is one of the most destructive diseases of melon and watermelon in many countries. Pathogen-free seed and cultural practices are major pillars of the disease control. However, use of bacteriophages as natural biocontrol agents might also contribute to the disease management. Therefore, we isolated 12 bacteriophages specific to A. citrulli, from phyllosphere and rhizosphere of diseased watermelon plants. The phage strains were characterized based on their host range, plaque and virion morphology, thermal inactivation point, adsorption rate, one step growth curve, restriction fragment length polymorphism (RFLP), and genomic analysis. Transmission electron microscopy of three phage strains indicated that they belong to the order Caudovirales, family Siphoviridae. All phages lysed 30 out of 32 tested A. citrulli strains isolated in Serbia, and did not lyse other less related bacterial species. They produced clear plaques, 2 mm in diameter, on bacterial lawns of different A. citrulli strains after 24 h of incubation. The thermal inactivation point was 66 or 67°C. They were stable at pH 5–9, but were sensitive to chloroform and inactivated in either 5 or 10 min exposure to ultraviolet (UV) light. RFLP analysis using EcoRI, BsmI and BamHI enzymes did not show genetic differences among the tested phages. Adsorption rate and one step growth curve were determined for the Acidovorax phage ACF1. Draft genome sequence of the ACF1 phage was 59.377 bp in size, with guanine-cytosine (GC) content 64.5%, including 89 open reading frames. This phage shared a very high genomic identity with Acidovorax phage ACPWH, isolated in South Korea. Evaluation of systemic nature of ACF1 strain showed that it can be absorbed by roots and translocated to upper parts of watermelon plants where it survived up to 10 days.

Prospects of bacteriophage collections in disinfectant applications.

Background and Aim:The search and development of disinfectants is promising worldwide. However, there are currently no international regulations governing the testing and registration of germicidal agents. Moreover, the number of safety requirements for disinfectants for human, animal, and environmental health has increased. This research aimed to evaluate the prospects of using a collection of bacteriophages for disinfectant purposes.Materials and Methods:The objects of research were bacteriophages isolated from a total of 129 environmental samples obtained from seven sources in and around livestock buildings: (1) Feed residues from feeders and automatic drinkers; (2) washouts from floors, walls, and posts; (3) soil from underneath floors; (4) bedding; (5) sewage; (6) ponds; and (7) soil from paddocks. The corresponding strains were used as indicator test cultures for bacteriophages. The authors employed the following methods to work with bacteriophages: (a) Bacteriophage isolation methods, (b) the Appelman method (i.e., serial dilutions), (c) the Grazia method (i.e., agar layers), (d) phage titration on solid media, and (e) the bacterial phagotyping method.Results:The results of the analysis on the bacteria of the Enterobacteriaceae family isolated 11 bacteriophages; one bacteriophage is specific to Pseudomonas aeruginosa, and another one is specific to Brucella abortus. The results also indicate that all bacteriophage strains of the Enterobacteriaceae family demonstrate lysis at a pH of 7.0. In addition, this polyphage lyses all strains of sensitive bacterial cultures. The optimum temperature for the cultivation of bacteriophages is 35°C. While using electron microscopy to study the consortium of bacteriophages, clearly distinguishable virions of bacteriophages were found in the microscope field of view.Conclusion:The main parameters for the production of polyphages include the ratio of the bacteriophage and its corresponding bacteriophage-sensitive culture, the pH of the cultivation medium, and the cultivation time of the bacteriophage system as well as the sensitive bacterium. With regard to the aforementioned parameters, the results indicate that the average value for all bacteriophages is 1:2, and the average cultivation medium pH is 7.0 for all bacteriophages. The average cultivation time for all bacteriophages is 18-24 h.

Comparision of biological and genomic characteristics of five virulent bacteriophages against Enterobacter hormaechei

Enterobacter hormaechei is a zoonotic bacteria that may cause respiratory diseases in animals and neonatal sepsis in humans. Bacteriophages are increasingly considered as potential biocontrol agents to control pathogens in the food industry. In this study, five E. hormaechei virulent phages, named as Ehp-YZU08, Ehp-YZU10, Ehp-YZU9-1, Ehp-YZU9-2 and Ehp-YZU9-3, were isolated from sewage in China and analyzed for their biological and whole-genome characteristics, and a comparative genomic analysis was performed to study the functional genes and phylogenetic evolution of phages. The results showed that four of the phage strains belong to the Podoviridae family and one belongs to the Myoviridae family. The burst sizes were 70–283 PFU/cell after a latent period of 5–40 min. Phages were able to survive in a pH range of 5–10 and resist temperatures up to 60 °C for 60 min. The sequencing results showed that the full length of the genomes of the five phages ranged from 39,502 to 173,418 bp. Each phage contained multiple genes related to phage replication, and genes related to bacterial virulence or drug resistance were not found. The five phages belonged to three different groups by a construction of a phylogenetic tree, and the significant genetic evolutionary distance from each E. hormaechei phage was observed. The inhibition assay showed that all five phages could completely inhibit the growth of E. hormaechei at 37 °C within 8 h, suggesting that the phages in this study have great potential for the development of biocontrol agents against E. hormaechei in the food industry.

ТЕХНОЛОГИЯ ИЗГОТОВЛЕНИЯ И КОНТРОЛЯ ФАГОВОГО БИОПРЕПАРАТА XANTHOMONAS CAMPESTRIS

Traditional methods of combating bacterial diseases of plants, including vascular bacteriosis of Cruciferous plants, do not currently allow to achieve effective result, which, among other things, is associated with the ability of phytopathogens to adapt to changing environmental conditions. Application of bacteriophages as antibacterial agents is a farsighted and effective direction in the field of plant protection. The aim of the study was to develop a technology for production and control of Xanthomonas campestris phage biological product, taking into account previously defined technological parameters. The objects of the study were X. campestris pv. campestris Cl34-UlSAU bacteriophage isolated from cabbage samples with signs of vascular bacteriosis from the fields of Ulyanovsk region, Staromainsky district. As a production strain, we used X. campestris pv. campestris Xc2 bacterial strain. The authors carried out studies on selection of suitable conditions, taking into account previously defined parameters: a method for bacteriophage removal from a production culture of bacteria, suitable passage time for production of a phage preparation, appropriate balance of phage and bacterial culture for cultivation, suitable temperature for bacteriophage cultivation. The paper introduces a scheme for production and control of Xanthomonas campestris pv. campestris phage biological product, which consists of 4 stages: sample preparation of a production culture of bacteria for compliance with the properties of the declared strain, sample preparation of a production strain of Kl34-UlSAU bacteriophage for compliance with its activity after storage, production of a phage product with reference to production scaling, pouring, purity control, bacteriophage titer, its specificity and spectrum of lytic action, storage of a biological product.

Isolation and Identification of a Vibrio alginolyticus Bacteriophage Va2001 and Its Application to Oysters

In order to develop the cleaning agent for Vibrio alginolyticus in aquatic products, about 60 pieces of seafood and sewage in their breeding environment were collected from aquatic product market and farmer’s market in Jinzhou City, Bijiashan sea area, supermarkets, an aquaculture farm in Huludao City, and a breeding farm in Anshan City, etc. A virulent phage strain, named Va2001, was obtained by isolating and purifying with double-layer plate method. The biological characteristics of Va2001, such as the lysis spectrum, optimal multiplicity of infection, one-step growth curve, temperature, and pH stability, were studied. In addition, the effect of bacteriophages clearing V. alginolyticus was determined in the oyster infection model. The results showed that the phage Va2001 belongs to the Podoviridae family of order Caudovirales. Va2001 had a narrow lysis spectrum, with a lysis rate of 32%. The optimal multiplicity of infection was 0.0001 and the incubation period was about 20 min. The lytic period was 100 min and the average burst size was 274 PFU/cell. The activity was stable in the range of 4~60 ℃ and pH4~9. The results of the cleaning test using oysters as the infection model showed that the bacteriophage Va2001 could inhibit the growth of V. alginolyticus in the breeding environment and reduce the content of V. alginolyticus in oysters. When the breeding time was extended to 72 hours, the number of V. alginolyticus in the experiment group decreased by about 2 lg. The results of this study indicate that the bacteriophage Va2001 has good application prospects and can be used as a new biological cleaning agent of V. alginolyticus in seafood.

A century of phage therapy: from novel discoveries about the past to the challenges of the today.

The discovery of bacterial viruses able to kill bacteria, named bacteriophages (phages), more than a century ago, contributed to combating bacterial infections during the first three decades of the 20th century. Vladimir Sertić, a Croatian microbiologist, was one of the pioneers in bacteriophages investigation, who performed significant scientific research on phage strains characterization, isolation, and classification. The important contribution of Vladimir Sertić can be seen from his private archive (from the 1930s) which contains hundreds of valuable archival materials that are today kept at the Department of Pharmacology School of Medicine, Zagreb. The Discovery of this archive was recently described by Lackovic and Toljan. Here we describe a further survey of this archive. In addition to many documents, it contains phage cocktails in a small commercial paper box, with instructions for usage, as clear evidence of their therapeutic application in the pre-antibiotic era. This revelation, not shown in the literature up to now, to the best of our knowledge, motivated us to present it to the wider scientific and professional community with this short article, giving an additional brief overview of the current perspective of phage investigation and therapeutic application.

Efficacy of Novel Bacteriophages against Escherichia coli Biofilms on Stainless Steel

Biofilm formation by E. coli is a serious threat to meat processing plants. Chemical disinfectants often fail to eliminate biofilms; thus, bacteriophages are a promising alternative to solve this problem, since they are widely distributed, environmentally friendly, and nontoxic to humans. In this study, the biofilm formation of 10 E. coli strains isolated from the meat industry and E. coli ATCC BAA-1430 and ATCC 11303 were evaluated. Three strains, isolated from the meat contact surfaces, showed adhesion ability and produced extracellular polymeric substances. Biofilms of these three strains were developed onto stainless steel (SS) surfaces and enumerated at 2, 12, 24, 48, and 120 h, and were visualized by scanning electron microscopy. Subsequently, three bacteriophages showing podovirus morphology were isolated from ground beef and poultry liver samples, which showed lytic activity against the abovementioned biofilm-forming strains. SS surfaces with biofilms of 2, 14, and 48 h maturity were treated with mixed and individual bacteriophages at 8 and 9 log10 PFU/mL for 1 h. The results showed reductions greater than 6 log10 CFU/cm2 as a result of exposing SS surfaces with biofilms of 24 h maturity to 9 log10 PFU/mL of bacteriophages; however, the E. coli and bacteriophage strains, phage concentration, and biofilm development stage had significant effects on biofilm reduction (p < 0.05). In conclusion, the isolated bacteriophages showed effectiveness at reducing biofilms of isolated E. coli; however, it is necessary to increase the libraries of phages with lytic activity against the strains isolated from production environments.

Use of Phage Cocktail for Improving the Overall Microbiological Quality of Sprouts—Two Methods of Application

Background: the aim of this study was to improve the overall microbiological quality of five different sprouts (alfalfa, kale, lentil, sunflower, radish) using newly isolated bacteriophages. Method: in this study we had isolated from sewage 18 bacteriophages targeting bacteria dominant in sprouts. Five selected bacteriophage strains were photographed using a transmission electron microscope (TEM), and we analyzed the rate of attachment, resistance to chloroform, the burst size, and the latency period. Two methods of application of the phage cocktail were investigated: spraying, and an absorption pad. Results: the spraying method was significantly more efficient, and the maximum reduction effect after 48 h of incubation was 1.5 log CFU/g. Using pads soaked with phage lysate reduced the total number of bacteria to only about 0.27–0.79 log CFU/g. Conclusion: the reduction of bacteria levels in sprouts depended on the method of phage application. The blind strategy for searching phage targeting bacteria dominant in sprouts can be useful and economically beneficial as a starting point for further investigation in phage cocktail application for improving the overall microbiological quality of food. The main result of our research is to improve the overall quality of kale and radish sprouts by spraying them with a phage cocktail.

Dynamics of Baltic Sea phages driven by environmental changes.

Phage predation constitutes a major mortality factor for bacteria in aquatic ecosystems, and thus, directly impacts nutrient cycling and microbial community dynamics. Yet, the population dynamics of specific phages across time scales from days to months remain largely unexplored, which limits our understanding of their influence on microbial succession. To investigate temporal changes in diversity and abundance of phages infecting particular host strains, we isolated 121 phage strains that infected three bacterial hosts during a Baltic Sea mesocosm experiment. Genome analysis revealed a novel Flavobacterium phage genus harboring gene sets putatively coding for synthesis of modified nucleotides and glycosylation of bacterial cell surface components. Another novel phage genus revealed a microdiversity of phage species that was largely maintained during the experiment and across mesocosms amended with different nutrients. In contrast to the newly described Flavobacterium phages, phages isolated from a Rheinheimera strain were highly similar to previously isolated genotypes, pointing to genomic consistency in this population. In the mesocosm experiment, the investigated phages were mainly detected after a phytoplankton bloom peak. This concurred with recurrent detection of the phages in the Baltic Proper during summer months, suggesting an influence on the succession of heterotrophic bacteria associated with phytoplankton blooms.

How to Train Your Phage: The Recent Efforts in Phage Training

Control of pathogenic bacteria by deliberate application of predatory phages has potential as a powerful therapy against antibiotic-resistant bacteria. The key advantages of phage biocontrol over antibacterial chemotherapy are: (1) an ability to self-propagate inside host bacteria, (2) targeted predation of specific species or strains of bacteria, (3) adaptive molecular machinery to overcome resistance in target bacteria. However, realizing the potential of phage biocontrol is dependent on harnessing or adapting these responses, as many phage species switch between lytic infection cycles (resulting in lysis) and lysogenic infection cycles (resulting in genomic integration) that increase the likelihood of survival of the phage in response to external stress or host depletion. Similarly, host range will need to be optimized to make phage therapy medically viable whilst avoiding the potential for deleteriously disturbing the commensal microbiota. Phage training is a new approach to produce efficient phages by capitalizing on the evolved response of wild-type phages to bacterial resistance. Here we will review recent studies reporting successful trials of training different strains of phages to switch into lytic replication mode, overcome bacterial resistance, and increase their host range. This review will also highlight the current knowledge of phage training and future implications in phage applications and phage therapy and summarize the recent pipeline of the magistral preparation to produce a customized phage for clinical trials and medical applications.

Overcoming the growth-infectivity trade-off in a bacteriophage slows bacterial resistance evolution.

The use of lytic bacteriophages for treating harmful bacteria (phage therapy) is faced with the challenge of bacterial resistance evolution. Phage strains with certain traits, for example, rapid growth and relatively broad infectivity ranges, may enjoy an advantage in slowing bacterial resistance evolution. Here, we show the possibility for laboratory selection programs (“evolutionary training”) to yield phage genotypes with both high growth rate and broad infectivity, traits between which a trade‐off has been assumed. We worked with a lytic phage that infects the bacterium Pseudomonas fluorescens and adopted three types of training strategies: evolution on susceptible bacteria, coevolution with bacteria, and rotation between evolution and coevolution phases. Overall, there was a trade‐off between growth rate and infectivity range in the evolved phage isolates, including those from the rotation training programs. A small number of phages had both high growth rate and broad infectivity, and those trade‐off‐overcoming phages could slow or even completely prevent resistance evolution in initially susceptible bacterial populations. Our findings show the promise of well‐designed evolutionary training programs, in particular an evolution/coevolution rotation selection regime, for obtaining therapeutically useful phage materials.