Isolation of phages for phage therapy: a comparison of spot tests and efficiency of plating analyses for determination of host range and efficacy

Bacteriophage cocktail for biocontrol of soft rot disease caused by Pectobacterium species in Chinese cabbage

Pectobacterium spp. are necrotrophic plant pathogens that cause the soft rot disease in Chinese cabbage, resulting in severe yield loss. The use of conventional antimicrobial agents, copper-based bactericides, and antibiotics has encountered several limitations, such as bioaccumulation on plants and microbial resistance. Bacteriophages (phages) are considered promising alternative antimicrobial agents against diverse phytopathogens. In this study, we isolated and characterized two virulent phages (phiPccP-2 and phiPccP-3) to develop a phage cocktail. Morphological and genomic analyses revealed that two phages belonged to the Tevenvirinae and Mccorquodalevirinae subfamilies, respectively. The phiPccP-2 and phiPccP-3 phages, which have a broad host range, were stable at various environmental conditions, such as various pHs and temperatures and exposure to ultraviolet light. The phage cocktail developed using these two lytic phages inhibited the emergence of phage-resistant bacteria compared to single-phage treatments in in vitro challenge assays. The phage cocktail treatment effectively prevented the development of soft rot symptom in matured Chinese cabbage leaves. Additionally, the phage cocktail comprising three phages (phiPccP-1, phiPccP-2, and phiPccP-3) showed superior biocontrol efficacy against the mixture of Pectobacterium strains in Chinese cabbage seedlings. These results suggest that developing phage cocktails is an effective approach for biocontrol of soft rot disease caused by Pectobacterium strains in crops compared to single-phage treatments. KEY POINTS: •Two newly isolated Pectobacterium phages, phiPccP-2 and phiPccP-3, infected diverse Pectobacterium species and effectively inhibited the emergence of phage-resistant bacteria. •Genomic and physiological analyses suggested that both phiPccP-2 and phiPccP-3 are lytic phages and that their lytic activities are stable in the environmental conditions under which Chinese cabbage grows. •Treatment using a phage cocktail comprising phiPccP-2 and phiPccP-3 efficiently suppressed soft rot disease in detached mature leaves and seedlings of Chinese cabbage, indicating the applicability of the phage cocktail as an alternative antimicrobial agent.

Characterization and genome analysis of a broad host range lytic phage vB_SenS_TUMS_E19 against Salmonella enterica and its efficiency evaluation in the liquid egg

Salmonella enterica serovars are zoonotic bacterial that cause foodborne enteritis. Due to bacteria's antibiotic resistance, using bacteriophages for biocontrol and treatment is a new therapeutic approach. In this study, we isolated, characterized, and analyzed the genome of vB_SenS_TUMS_E19 (E19), a broad host range Salmonella bacteriophage, and evaluated the influence of E19 on liquid eggs infected with Salmonella enterica serovar Enteritidis. Transmission electron microscopy showed that the isolated bacteriophage had a siphovirus morphotype. E19 showed rapid adsorption (92% in 5 min), a short latent period (18 min), a large burst size (156 PFU per cell), and a broad host range against different Salmonella enterica serovars. Whole-genome sequencing analysis indicated that the isolated phage had a 42 813 bp long genome with 49.8% G + C content. Neither tRNA genes nor those associated with antibiotic resistance, virulence factors, or lysogenic formation were detected in the genome. The efficacy of E19 was evaluated in liquid eggs inoculated with S. Enteritidis at 4 and 25 °C, and results showed that it could effectively eradicate S. Enteritidis in just 30 min and prevented its growth up to 72 h. Our findings indicate that E19 can be an alternative to a preservative to control Salmonella in food samples and help prevent and treat salmonellosis.

PhagoScreener: A novel phagogram platform based on a capillary-wave microbioreactor

Due to the overuse of antibiotics, the number of multidrug-resistant pathogen bacteria is rising in recent years posing a serious threat to human health. One promising alternative for treatment is the application of phage therapy using highly selective bacteriophages. Because of their selectivity, individual screens called phagograms for each patient are required to select phages from a phage library. Phagograms are mostly performed via bacterial cultivation on double layer agar plates and phage addition causing bacterial lysis. However, these assays are work-intensive and have a low ability for parallelization and automation. Hence, highly parallelizable and automatable microbioreactors in the lowest microliter scale could offer an economic solution increasing the throughput of phagograms. This paper demonstrates the applicability of a novel capillary-wave microbioreactor (cwMBR) to perform phagograms. Due to its small volume of only 7 µL and the open-droplet design, it can be easily automated and parallelized in future. Furthermore, the ability of online biomass measurement makes the cwMBR a perfect phagogram platform in the future. Herein, phagograms with E. coli and different concentrations of the phages MM02 and EASG3 were performed as proof of concept for phagograms in the cwMBR. Thereby, the cwMBR was able to measure differences in lysis kinetics of different phages. Furthermore, the phagograms were compared to those in conventional microtiter plate readers revealing the cwMBR as ideal alternative for phagograms as it combines favorable mixing conditions and a phage repellent hydrophilic glass surface with online biomass measurement in an open-droplet design for future parallelization and automation.

Phage therapy combats pan drug-resistant Acinetobacter baumannii infection safely and efficiently

Phage therapy offers a promising approach to combat the growing threat of antimicrobial resistance. Yet, key questions remain regarding dosage, administration routes, combination therapy, and the causes of therapeutic failure. In this study, we focused on a novel lytic phage, ФAb4B, which specifically targeted the Acinetobacter baumannii strains with KL160 capsular polysaccharide, including the pan-drug resistant A. baumannii YQ4. ФAb4B exhibited the ability to effectively inhibit biofilm formation and eradicate mature biofilms independently of dosage. Additionally, it demonstrated a wide spectrum of antibiotic-phage synergy and did not show any cytotoxic or haemolytic effects. Continuous phage injections, both intraperitoneally and intravenously over 7 d, showed no acute toxicity in vivo. Importantly, phage therapy significantly improved neutrophil counts, outperforming ciprofloxacin. However, excessive phage injections suppressed neutrophil levels. The combinatorial treatment of phage-ciprofloxacin rescued 91% of the mice, a superior outcome compared to phage alone (67%). The efficacy of the combinatorial treatment was independent of phage dosage. Notably, prophylactic administration of the combinatorial regimen provided no protection, but even when combined with a delayed therapeutic regimen, it saved all the mice. Bacterial resistance to the phage was not a contributing factor to treatment failure. Our preclinical study systematically describes the lytic phage's effectiveness in both in vitro and in vivo settings, filling in crucial details about phage treatment against bacteriemia caused by A. baumannii, which will provide a robust foundation for the future of phage therapy.

Bacteriophage-Based Bioanalysis

Bacteriophages, which are viral predators of bacteria, have evolved to efficiently recognize, bind, infect, and lyse their host, resulting in the release of tens to hundreds of propagated viruses. These abilities have attracted biosensor developers who have developed new methods to detect bacteria. Recently, several comprehensive reviews have covered many of the advances made regarding the performance of phage-based biosensors. Therefore, in this review, we first describe the landscape of phage-based biosensors and then cover advances in other aspects of phage biology and engineering that can be used to make high-impact contributions to biosensor development. Many of these advances are in fields adjacent to analytical chemistry such as synthetic biology, machine learning, and genetic engineering and will allow those looking to develop phage-based biosensors to start taking alternative approaches, such as a bottom-up design and synthesis of custom phages with the singular task of detecting their host.

Isolation, characterization, and application of bacteriophage on Vibrio parahaemolyticus biofilm to control seafood contamination

OBJECTIVE

This study intended to isolate a Vibrio-particular phage from the natural environment, analyse its characteristics and genome sequence, and investigate its reduction effect on V. parahaemolyticus biofilm as a biocontrol agent in squid and mackerel.

METHODS

Among 21 phages, phage CAU_VPP01, isolated from beach mud, was chosen for further experiments based on host range and EOP tests. When examining the reduction effect of phage CAU_VPP01 against Vibrio parahaemolyticus biofilms on surfaces (stainless steel [SS] and polyethylene terephthalate [PET]) and food surfaces (squid and mackerel).

RESULTS

The phage showed the most excellent reduction effect at a multiplicity-of-infection (MOI) 10. Three-dimensional images acquired with confocal laser scanning microscopy (CLSM) analysis were quantified using COMSTAT, which showed that biomass, average thickness, and roughness coefficient decreased when treated with the phage. Colour and texture analysis confirmed that the quality of squid and mackerel was maintained after the phage treatment. Finally, a comparison of gene expression levels determined by qRT-PCR analysis showed that the phage treatment induced a decrease in the gene expression of flaA, vp0962, andluxS, as examples.

CONCLUSION

This study indicated that Vibrio-specific phage CAU_VPP01 effectively controlled V. parahaemolyticus biofilms under various conditions and confirmed that the isolated phage could possibly be used as an effective biocontrol weapon in the seafood manufacturing industry.

Biological and genomic characteristics of three novel bacteriophages and a phage-plasmid of Klebsiella pneumoniae

Bacteriophages have emerged as promising candidates for the treatment of difficult-to-treat bacterial infections. The aim of this study is to isolate and characterize phages infecting carbapenem-resistant and extended-spectrum beta-lactamase producer Klebsiella pneumoniae isolates. Water samples were taken for the isolation of bacteriophages. One-step growth curve, the optimal multiplicity of infection (MOI), thermal and pH stabilities, transmission electron microscopy and whole-genome sequencing of phages were studied. Four phages were isolated and named Klebsiella phage Kpn02, Kpn17, Kpn74, and Kpn13. The optimal MOI and latent periods of phage Kpn02, Kpn17, Kpn74, and Kpn13 were 10, 1, 0.001, and 100 PFU/CFU and 20, 10, 20, and 30 min, respectively. Burst sizes ranged from 811 to 2363. No known antibiotic resistance and virulence genes were identified. No tRNAs were detected except Klebsiella phage Kpn02 which encodes 24 tRNAs. Interestingly, Klebsiella phage Kpn74 was predicted to be a lysogenic phage whose prophage is a linear plasmid molecule with covalently closed ends. Of the Klebsiella-infecting phages presented in current study, virulent phages suggest that they may represent candidate therapeutic agents against MDR K. pneumoniae, based on short latent period, high burst sizes and no known antibiotic resistance and virulence genes in their genomes.

Bacteriophages to control Vibrio alginolyticus in live feeds prior to their administration in larviculture

AIMS

This study aimed to evaluate the efficiency of two phages [VB_VaC_TDDLMA (phage TDD) and VB_VaC_SRILMA (phage SRI)] alone and in a cocktail to control Vibrio alginolyticus in brine shrimp before their administration in larviculture.

METHODS AND RESULTS

Phages were isolated from seawater samples and characterized by host spectrum, growth parameters, adsorption rate, genomic analysis, and inactivation efficiency. Both phages belong to the Caudoviricetes class and lack known virulence or antibiotic-resistance genes. They exhibit specificity, infecting only their host, V. alginolyticus CECT 521. Preliminary experiments in a culture medium showed that phage TDD (reduction of 5.8 log CFU ml-1 after 10 h) outperformed phage SRI (reduction of 4.6 log CFU ml-1 after 6 h) and the cocktail TDD/SRI (reduction of 5.2 log CFU ml-1 after 8 h). In artificial marine water experiments with Artemia franciscana, both single phage suspensions and the phage cocktail, effectively inactivated V. alginolyticus in culture water (reduction of 4.3, 2.1, and 1.9 log CFU ml-1 for phages TDD, SRI, and the phage cocktail, respectively, after 12 h) and in A. franciscana (reduction of 51.6%, 87.3%, and 85.3% for phages TDD, SRI, and the phage cocktail, respectively, after 24 h). The two phages and the phage cocktail did not affect A. franciscana natural microbiota or other Vibrio species in the brine shrimp.

CONCLUSIONS

The results suggest that phages can safely and effectively control V. alginolyticus in A. franciscana prior to its administration in larviculture.

vB_EcoM-P896 coliphage isolated from duck sewage can lyse both intestinal pathogenic Escherichia coli and extraintestinal pathogenic E. coli

Pathogenic Escherichia coli strains cause diseases in both humans and animals. The limiting factors to prevent as well as control infections from pathogenic E. coli strains are their pathotypes, serotypes, and drug resistance. Herein, a bacteriophage (vB_EcoM-P896) has been isolated from duck sewage. Furthermore, aside from targeting intestinal pathogenic E. coli strains like enteropathogenic E. coli, Shiga toxin-producing E. coli, entero-invasive E. coli, and enteroaggregative E. coli, vB_EcoM-P896 can cause lysis in extraintestinal pathogenic E. coli strains such as avian pathogenic E. coli. Stability analysis revealed that vB_EcoM-P896 was stable under the following conditions: temperature, 4℃-50℃; pH, 3-11. The sequencing of the vB_EcoM-P896 genome was conducted utilizing an HiSeq system (Illumina, San Diego, CA) and subjected to de novo assembling with the aid of Spades 3.11.1. The characteristics of the DNA genome were as follows: size, 170,656 bp; GC content, 40.4%; the number of putative coding regions, 294. Transmission electron microscopy analysis of morphology and genome analysis revealed that the phage vB_EcoM-P896 belonged to the order Caudovirales and the family Myoviridae. The pan-genome analysis of vB_EcoM-P896 was divided into two levels. The first level involved the analysis of 91 strains of muscle tail phages, which were mainly divided into 5 groups. The second level involved the analysis of 24 strains of myophage with high homology. Of the 1480 gene clusters, 23 were shared core genes. Neighbor-joining phylogenetic trees were constructed using the Poisson model with MEGA6.0 based on the conserved sequences of phage proteins, the amino acid sequence of the terminase large subunit, and tail fibrin. Further analysis revealed that vB_EcoM-P896 was a typical T4-like potent phage with potential clinical applications.

Genomic and Phenotypic Analysis of Salmonella enterica Bacteriophages Identifies Two Novel Phage Species

Bacteriophages (phages) are potential alternatives to chemical antimicrobials against pathogens of public health significance. Understanding the diversity and host specificity of phages is important for developing effective phage biocontrol approaches. Here, we assessed the host range, morphology, and genetic diversity of eight Salmonella enterica phages isolated from a wastewater treatment plant. The host range analysis revealed that six out of eight phages lysed more than 81% of the 43 Salmonella enterica isolates tested. The genomic sequences of all phages were determined. Whole-genome sequencing (WGS) data revealed that phage genome sizes ranged from 41 to 114 kb, with GC contents between 39.9 and 50.0%. Two of the phages SB13 and SB28 represent new species, Epseptimavirus SB13 and genera Macdonaldcampvirus, respectively, as designated by the International Committee for the Taxonomy of Viruses (ICTV) using genome-based taxonomic classification. One phage (SB18) belonged to the Myoviridae morphotype while the remaining phages belonged to the Siphoviridae morphotype. The gene content analyses showed that none of the phages possessed virulence, toxin, antibiotic resistance, type I-VI toxin-antitoxin modules, or lysogeny genes. Three (SB3, SB15, and SB18) out of the eight phages possessed tailspike proteins. Whole-genome-based phylogeny of the eight phages with their 113 homologs revealed three clusters A, B, and C and seven subclusters (A1, A2, A3, B1, B2, C1, and C2). While cluster C1 phages were predominantly isolated from animal sources, cluster B contained phages from both wastewater and animal sources. The broad host range of these phages highlights their potential use for controlling the presence of S. enterica in foods.

Preclinical characterization and in silico safety assessment of three virulent bacteriophages targeting carbapenem-resistant uropathogenic Escherichia coli

Phage therapy has recently been revitalized in the West with many successful applications against multi-drug-resistant bacterial infections. However, the lack of geographically diverse bacteriophage (phage) genomes has constrained our understanding of phage diversity and its genetics underpinning host specificity, lytic capability, and phage-bacteria co-evolution. This study aims to locally isolate virulent phages against uropathogenic Escherichia coli (E. coli) and study its phenotypic and genomic features. Three obligately virulent Escherichia phages (øEc_Makalu_001, øEc_Makalu_002, and øEc_Makalu_003) that could infect uropathogenic E. coli were isolated and characterized. All three phages belonged to Krischvirus genus. One-step growth curve showed that the latent period of the phages ranged from 15 to 20 min, the outbreak period ~ 50 min, and the burst size ranged between 74 and 127 PFU/bacterium. Moreover, the phages could tolerate a pH range of 6 to 9 and a temperature range of 25-37 °C for up to 180 min without significant loss of phage viability. All phages showed a broad host spectrum and could lyse up to 30% of the 35 tested E. coli isolates. Genomes of all phages were approximately ~ 163 kb with a gene density of 1.73 gene/kbp and an average gene length of ~ 951 bp. The coding density in all phages was approximately 95%. Putative lysin, holin, endolysin, and spanin genes were found in the genomes of all three phages. All phages were strictly virulent with functional lysis modules and lacked any known virulence or toxin genes and antimicrobial resistance genes. Pre-clinical experimental and genomic analysis suggest these phages may be suitable candidates for therapeutic applications.

Isolation and characterization of lytic bacteriophages from various sources in Addis Ababa against antimicrobial-resistant diarrheagenic Escherichia coli strains and evaluation of their therapeutic potential

BACKGROUND

Escherichia coli is a common fecal coliform, facultative aerobic, gram-negative bacterium. Pathogenic strains of such microbes have evolved to cause diarrhea, urinary tract infections, and septicemias. The emergence of antibiotic resistance urged the identification of an alternative strategy. The use of lytic bacteriophages against the control of pathogenic E. coli in clinics and different environmental setups (waste and drink water management) has become an alternative therapy to antibiotic therapy. Thus, this study aimed to isolate and characterize lytic bacteriophage from various sources in Addis Ababa, tested them against antimicrobial-resistant diarrheagenic E. coli strains and evaluated their therapeutic potential under in vitro conditions.

METHODS

A total of 14 samples were processed against six different diarrheagenic E. coli strains. The conventional culture and plaque analysis agar overlay method was used to recover lytic bacteriophage isolates. The phage isolates were characterized to determine their lytic effect, growth characteristics, host range activity, and stability under different temperature and pH conditions. Phage isolates were identified by scanning electron microscope (SEM), and molecular techniques (PCR).

RESULTS

In total, 17 phages were recovered from 84 tested plates. Of the 17 phage isolates, 11 (65%) were Myoviridae-like phages, and 6 (35%) phage isolates were Podoviridae and Siphoviridae by morphology and PCR identification. Based on the host range test, growth characteristics, and stability test 7 potent phages were selected. These phages demonstrated better growth characteristics, including short latent periods, highest burst sizes, and wider host ranges, as well as thermal stability and the ability to survive in a wide range of pH levels.

CONCLUSIONS

The promising effect of the phages isolated in this study against AMR pathogenic E. coli has raised the possibility of their use in the future treatment of E. coli infections.

Isolation, Genomic Characterization of Shigella prophage fPSFA that effectively infects multi-drug resistant Shigella isolates from the Indian Poultry Sector

Because of uncontrolled use of antibiotics, emergence of multidrug-resistant Shigella species poses a huge potential of zoonotic transfer from poultry sector. With increasing resistance to current antibiotics, there is a critical need to explore antibiotic alternatives. Using a Shigella flexneri reference strain, we isolated a novel fPSFA phage after inducing with mitomycin C. The phage was found to be stable for wide ranges of temperature -20 °C-65 °C and pH 3 to 11. fPSFA shows a latent period that ranges from 20 to 30 min and generation times of 50-60 min. The genome analysis of phage reveals two major contigs of 23788 bp and 23285 bp with 50.16 % and 39.33 % G + C content containing a total of 80 CDS and 2 tRNA genes. The phage belongs to Straboviridae family and lacks any virulence or antimicrobial resistance gene, thus making it a suitable candidate for treatment of drug-resistant infections. To confirm lytic ability of novel phage, we isolated 54 multidrug-resistant Shigella species from thirty-five poultry fecal samples that shows multiple antibiotic resistance index ranging from 0.15 to 0.75 (from 3 Indian states). The fPSFA showed lytic activity against multidrug-resistant Shigella isolates (73.08 %) (MARI≥0.50). The wide host ranges of fPSFA phage demonstrate its potential to be used as a biocontrol agent.

Exploiting lung adaptation and phage steering to clear pan-resistant Pseudomonas aeruginosa infections in vivo

Pseudomonas aeruginosa is a major nosocomial pathogen that causes severe disease including sepsis. Carbapenem-resistant P. aeruginosa is recognised by the World Health Organisation as a priority 1 pathogen, with urgent need for new therapeutics. As such, there is renewed interest in using bacteriophages as a therapeutic. However, the dynamics of treating pan-resistant P. aeruginosa with phage in vivo are poorly understood. Using a pan-resistant P. aeruginosa in vivo infection model, phage therapy displays strong therapeutic potential, clearing infection from the blood, kidneys, and spleen. Remaining bacteria in the lungs and liver displays phage resistance due to limiting phage adsorption. Yet, resistance to phage results in re-sensitisation to a wide range of antibiotics. In this work, we use phage steering in vivo, pre-exposing a pan resistant P. aeruginosa infection with a phage cocktail to re-sensitise bacteria to antibiotics, clearing the infection from all organs.

High-Throughput Bacteriophage Testing with Potency Determination: Validation of an Automated Pipetting and Phage Drop-Off Method

The development of bacteriophages (phages) as active pharmaceutical ingredients for the treatment of patients is on its way and regulatory agencies are calling for reliable methods to assess phage potency. As the number of phage banks is increasing, so is the number of phages that need to be tested to identify therapeutic candidates. Currently, assessment of phage potency on a semi-solid medium to observe plaque-forming units is unavoidable and proves to be labor intensive when considering dozens of phage candidates. Here, we present a method based on automated pipetting and phage drop-off performed by a liquid-handling robot, allowing high-throughput testing and phage potency determination (based on phage titer and efficiency of plaquing). Ten phages were tested, individually and assembled into one cocktail, against 126 Escherichia coli strains. This automated method was compared to the reference one (manual assay) and validated in terms of reproducibility and concordance (ratio of results according to the Bland and Altman method: 0.99; Lin's concordance correlation coefficient: 0.86). We found that coefficients of variation were lower with automated pipetting (mean CV: 13.3% vs. 24.5%). Beyond speeding up the process of phage screening, this method could be used to standardize phage potency evaluation.

Diverse bacteriophages for biocontrol of ESBL- and AmpC-β-lactamase-producing E. coli

Novel solutions are needed to reduce the risk of transmission of extended spectrum β-lactamase (ESBL) and AmpC β-lactamase producing Escherichia coli (ESBL/AmpC E. coli) from livestock to humans. Given that phages are promising biocontrol agents, a collection of 28 phages that infect ESBL/AmpC E. coli were established. Whole genome sequencing showed that all these phages were unique and could be assigned to 15 different genera. Host range analysis showed that 82% of 198 strains, representing the genetic diversity of ESBL/AmpC E. coli, were sensitive to at least one phage. Identifying receptors used for phage binding experimentally as well as in silico predictions, allowed us to combine phages into two different cocktails with broad host range targeting diverse receptors. These phage cocktails efficiently inhibit the growth of ESBL/AmpC E. coli in vitro, thus suggesting the potential of phages as promising biocontrol agents.

Therapeutic Potential of a Novel Lytic Phage, vB_EclM_ECLFM1, against Carbapenem-Resistant Enterobacter cloacae

The global rise of multidrug-resistant Enterobacter cloacae strains, especially those that are resistant to carbapenems and produce metallo-β-lactamases, poses a critical challenge in clinical settings owing to limited treatment options. While bacteriophages show promise in treating these infections, their use is hindered by scarce resources and insufficient genomic data. In this study, we isolated ECLFM1, a novel E. cloacae phage, from sewage water using a carbapenem-resistant clinical strain as the host. ECLFM1 exhibited rapid adsorption and a 15-min latent period, with a burst size of approximately 75 PFU/infected cell. Its genome, spanning 172,036 bp, was characterized and identified as a member of Karamvirus. In therapeutic applications, owing to a high multiplicity of infection, ECLFM1 showed increased survival in zebrafish infected with E. cloacae. This study highlights ECLFM1's potential as a candidate for controlling clinical E. cloacae infections, which would help address challenges in treating multidrug-resistant strains and contribute to the development of alternative treatments.

Structural and Genomic Diversity of Bacteriophages

Bacteriophage diversity is a relatively unknown frontier that is rapidly being explored, leading to a wealth of new information. New bacteriophages are being discovered at an astounding rate via both phage isolation studies and metagenomic analyses. In addition, a nucleotide sequence-based viral taxonomic system has been developed to better handle this wealth of new information. As a result of these developments, phage scientists are transitioning from knowing that there must be huge numbers of diverse kinds of phage particles in natural environments to identifying the actual abundance and phage diversity that is present in specific environments. This review documents the beginning of this transition, offering a glimpse into the magnitude of change unfolding in the field. It stands as a testament to the expanding frontiers of phage research, illuminating the remarkable progress made in unraveling the intricate world of bacteriophage diversity and advancing our understanding of these enigmatic viral entities.

Isolation, characterization, and application of lytic bacteriophages for controlling Enterobacter cloacae complex (ECC) in pasteurized milk and yogurt

Reducing bacterial pathogen contamination not only improves overall global public health but also diminishes food waste and loss. The use of lytic bacteriophages (phages) that infect and kill bacteria could be a beneficial tool for suppressing bacterial growth during dairy products storage time. Four Enterobacter cloacae (E. cloacae) complex isolates which were previously isolated from contaminated dairy products were used to identify lytic phages in wastewater. Phages specific to multi-drug resistant (MDR) E. cloacae complex 6AS1 were isolated from local sewage. Two novel phages vB_EclM-EP1 and vB_EclM-EP2 were identified as myoviral particles and have double-stranded DNA genome. Their host range and lytic capabilities were detected using spot test and efficiency of plating (EOP) against several bacterial isolates. The phages had a latent period of 30 min, and a large burst size of about 100 and 142 PFU/cell for vB_EclM-EP1 and vB_EclM-EP2, respectively. Both phages were viable at pH ranging 5-9 and stable at 70 °C for 60 min. The individual phages and their cocktail preparations (vB_EclM-EP1 and vB_EclM-EP2) reduced and inhibited the growth of E. cloacae complex 6AS1 during challenge test in milk and yogurt samples. These results indicate that the E. cloacae complex-specific phages (vB_EclM-EP1 and vB_EclM-EP2) have a potential application as microbicidal agents in packaged milk and milk derivatives during storage time. In addition, our environment is a rich sources of lytic phages which have potential use in eliminating multidrug-resistant isolates in food industry as well as in biocontrol.

Prevalence of Indigenous Antibiotic-Resistant Salmonella Isolates and Their Application to Explore a Lytic Phage vB_SalS_KFSSM with an Intra-Broad Specificity

The consumption of fresh produce has led to increase in antibiotic-resistant (AR) Salmonella outbreaks. In this study, indigenous Salmonella was isolated from a total of two hundred-two samples including fresh produce and agricultural environmental samples in Korea. After biochemical confirmation using the Indole, Methyl Red, Voges-Proskauer, Citrate tests, presumable Salmonella isolates were identified by 16S rRNA sequencing. Identified Salmonella isolates were evaluated for antibiotic susceptibility against twenty-two antibiotics. The specificity and the efficiency of plating (EOP) of vB_SalS_KFSSM were evaluated against fifty-three bacterial strains. Twenty-five suspected Salmonella were isolated and confirmed by the positive result for methyl red and citrate, of which ten were identified as Salmonella spp. through 16S rRNA gene sequencing. Eight Salmonella isolates (4.0%, n = 8/202) were resistant to at least one antibiotic, among which five were multi-drug resistant. As a lytic phage against Salmonella spp. CMGS-1, vB_SalS_KFSSM was isolated from cow manure. The phage was observed as a tailed phage belonging to the class Caudoviricetes. It exhibited an intra-broad specificity against four indigenous AR Salmonella isolates, two indigenous Salmonella isolates, and five other Salmonella serotypes with great efficiencies (EOP ≥ 0.75). Thus, this study suggested the potential of vB_SalS_KFSSM to combat indigenous AR Salmonella.

Genomic and proteomic characterization of vB_SauM-UFV_DC4, a novel Staphylococcus jumbo phage

Staphylococcus aureus is one of the most relevant mastitis pathogens in dairy cattle, and the acquisition of antimicrobial resistance genes presents a significant health issue in both veterinary and human fields. Among the different strategies to tackle S. aureus infection in livestock, bacteriophages have been thoroughly investigated in the last decades; however, few specimens of the so-called jumbo phages capable of infecting S. aureus have been described. Herein, we report the biological, genomic, and structural proteomic features of the jumbo phage vB_SauM-UFV_DC4 (DC4). DC4 exhibited a remarkable killing activity against S. aureus isolated from the veterinary environment and stability at alkaline conditions (pH 4 to 12). The complete genome of DC4 is 263,185 bp (GC content: 25%), encodes 263 predicted CDSs (80% without an assigned function), 1 tRNA (Phe-tRNA), multisubunit RNA polymerase, and an RNA-dependent DNA polymerase. Moreover, comparative analysis revealed that DC4 can be considered a new viral species belonging to a new genus DC4 and showed a similar set of lytic proteins and depolymerase activity with closely related jumbo phages. The characterization of a new S. aureus jumbo phage increases our understanding of the diversity of this group and provides insights into the biotechnological potential of these viruses. KEY POINTS: • vB_SauM-UFV_DC4 is a new viral species belonging to a new genus within the class Caudoviricetes. • vB_SauM-UFV_DC4 carries a set of RNA polymerase subunits and an RNA-directed DNA polymerase. • vB_SauM-UFV_DC4 and closely related jumbo phages showed a similar set of lytic proteins.

Newly isolated phages preying on Pseudomonas syringae pv. garcae: In vitro and ex vivo inactivation studies in coffee plant leafs

Coffee canker, or bacterial halo blight (BHB) of coffee, is a disease caused by the phytopathogenic bacterium Pseudomonas syringae pv. garcae (Psg), having been found for the first time in 1955, in the Garça region (State of São Paulo), and which has stood out in the Brazilian coffee plantations in recent years, leading to severe economic losses that seriously affect coffee trade. The treatments available are still scarce, involving frequent spraying of coffee plantations with either copper derivatives or the antibiotic kasugamycin. However, these compounds should be avoided due to environmental toxicity and the development of bacterial resistances. Herein we report the isolation and physical/biological characterisation of two novel lytic phages and their efficacy in the control of Psg. Phages ph002F and ph004F were isolated from coffee plant leaves in Brazil (Sorocaba/SP and Itu/SP cities), using Psg IBSBF-158 as the host. According to the transmission electron microscopy analyses, both phages belong to the class Caudoviricetes and present myovirus-like morphotypes. Phages ph002F and ph004F showed eclipse times of 5 min and 20 min, respectively, and a burst size of 123 PFU/host cell and 12 PFU/host cell, respectively, allowing to conclude they replicate well in Psg IBSBF-158 with latency periods of 50 min. Phage ph002F (reduction of 4.59 log CFU/mL, compared to uninfected culture) was more effective in inactivating Psg than phage ph004F (reduction of 3.85 log CFU/mL) after 10 h of incubation at a MOI of 10. As a cocktail, the two phages were highly effective in reducing the bacterial load (reduction of 5.26 log CFU/mL at a MOI of 0.1 or reduction of 5.03 log CFU/mL at a MOI of 10, relative to untreated culture), after 12 h of treatment. This study provides evidence that the isolated phages are promising candidates against the causative agent of BHB in coffee plants.

Potential application of phage vB_EfKS5 to control Enterococcus faecalis and its biofilm in food

Contaminated food with antibiotic-resistant Enterococcus spp. could be the vehicle for transmitting Enterococcus to humans and accordingly cause a public health problem. The accumulation of biogenic amines produced by Enterococcus faecalis (E. faecalis) in food may have cytological effects. Bacteriophages (phage in short) are natural antimicrobial agents and can be used alone or in combination with other food preservatives to reduce food microbial contaminants. The aim of this study was to isolate a novel phage against E. faecalis and determine its host range to evaluate its potential application. Bacteriophage, vB_EfKS5, with a broad host range, was isolated to control the growth of E. faecalis. The vB_EfKS5 genome is 59,246 bp in length and has a GC content of 39.7%. The computational analysis of phage vB_EfKS5 genome confirmed that it does not contain any lysogenic, toxic, or virulent genes. Phage vB_EfKS5 exhibited lytic activity against most E. faecalis isolates with different multiplicities of infections and it infected 75.5% (22/29) of E. faecalis isolates and 42.3% (3/7) of E. faecium isolates. It was also able to destroy the biofilm formed by E. faecalis with different MOIs. Phage vB_EfKS5 alone or in combination with nisin could control the growth of E. faecalis in broth and milk. Based on its high productivity, stability, short latent period, and large burst size, phage vB_EfKS5 has a high potential for applications both in food and medical applications.

Genomic analysis of K47-type Klebsiella pneumoniae phage IME305, a newly isolated member of the genus Teetrevirus

We isolated a K47-type Klebsiella pneumoniae phage from untreated hospital sewage: vB_KpnP_IME305 (GenBank no. OK149215). Next-generation sequencing (NGS) demonstrated that IME305 has a double-stranded DNA genome of 38,641 bp with 50.9% GC content. According to BLASTn comparisons, the IME305 genome sequence shares similarity with that of Klebsiella phage 6998 (97.37% identity and 95% coverage). IME305 contains 45 open reading frames (ORFs) and no rRNA, tRNA, or virulence-related gene sequences. Bioinformatic analysis showed that IME305 belongs to the phage subfamily Studiervirinae and genus Teetrevirus.

The effectiveness and role of phages in the disruption and inactivation of clinical P. aeruginosa biofilms

Biofilms of P. aeruginosa are known to be resilient forms of survival of this opportunistic pathogen, both within the host and in natural or engineered environments. This study investigated the role of phages in the disruption and inactivation of clinical P. aeruginosa biofilms by previously isolated phages. All seven tested clinical strains formed biofilms in 56-80 h. Four previously isolated phages were effective in disrupting the formed biofilms when applied at multiplicity of infection (MOI) of 10, where phage cocktails had equivalent or worse performance than single phages. Phage treatments reduced the biofilms' biomass (cells and extracellular matrix) by 57.6-88.5% after 72 h of incubation. Biofilm disruption led to the detachment of 74.5-80.4% of the cells. The phages were also able to kill the cells from the biofilms, reducing the living cell counts by approximately 40.5-62.0% after a single treatment. A fraction of 24-80% of these killed cells were also lysed due to phage action. This study showed that phages can have a relevant role in disrupting, inactivating, and destroying P. aeruginosa biofilms, which can be used in the development of treatment processes to complement or replace antibiotics and/or disinfectants.

Application of a novel phage LPCS28 for biological control of Cronobacter sakazakii in milk and reconstituted powdered infant formula

Contamination of infant formula with Cronobacter sakazakii (C. sakazakii) can cause fatal infections in neonates. Phages have emerged as promising antibacterial agents for food safety, but their effectiveness may be limited by thermal processing. In this study, we isolated 27 C. sakazakii phages from environmental water samples and selected LPCS28 due to its broad lysis spectrum. The titer of LPCS28 will not be significantly affected by heating at a temperature of 60 °C for one hour. In both reconstituted powdered infant formula (RPIF) and liquid milk, the pre-added LPCS28, after the thermal processing at 63 °C for 30 min, significantly inhibited the post-contaminated C. sakazakii (103 CFU/mL) and eventually reduced the number of C. sakazakii to below the limit of detection (<10 CFU/mL) within 9 h at 37 °C and significantly delayed the increase of bacterial concentration in the samples at 23 °C. The phylogenetic analysis revealed that LPCS28 belonged to a new genus, we proposed as Nanhuvirus, under the family Straboviridae. These findings suggest that phage LPCS28 is a promising biological control agent for pathogenic C. sakazakii in the dairy industry.

A novel lytic phage exhibiting a remarkable in vivo therapeutic potential and higher antibiofilm activity against Pseudomonas aeruginosa

BACKGROUND

Pseudomonas aeruginosa is a nosocomial bacterium responsible for variety of infections. Inappropriate use of antibiotics could lead to emergence of multidrug-resistant (MDR) P. aeruginosa strains. Herein, a virulent phage; vB_PaeM_PS3 was isolated and tested for its application as alternative to antibiotics for controlling P. aeruginosa infections.

METHODS

Phage morphology was observed using transmission electron microscopy (TEM). The phage host range and efficiency of plating (EOP) in addition to phage stability were analyzed. One-step growth curve was performed to detect phage growth kinetics. The impact of isolated phage on planktonic cells and biofilms was assessed. The phage genome was sequenced. Finally, the therapeutic potential of vB_PaeM_PS3 was determined in vivo.

RESULTS

Isolated phage has an icosahedral head and a contractile tail and was assigned to the family Myoviridae. The phage vB_PaeM_PS3 displayed a broad host range, strong bacteriolytic ability, and higher environmental stability. Isolated phage showed a short latent period and large burst size. Importantly, the phage vB_PaeM_PS3 effectively eradicated bacterial biofilms. The genome of vB_PaeM_PS3 consists of 93,922 bp of dsDNA with 49.39% G + C content. It contains 171 predicted open reading frames (ORFs) and 14 genes as tRNA. Interestingly, the phage vB_PaeM_PS3 significantly attenuated P. aeruginosa virulence in host where the survival of bacteria-infected mice was markedly enhanced following phage treatment. Moreover, the colonizing capability of P. aeruginosa was markedly impaired in phage-treated mice as compared to untreated infected mice.

CONCLUSION

Based on these findings, isolated phage vB_PaeM_PS3 could be potentially considered for treating of P. aeruginosa infections.

Genomic characterization of the novel bacteriophage IME183, infecting Klebsiella pneumoniae of capsular type K2

Klebsiella pneumoniae causes a wide range of serious and life-threatening infections. Klebsiella phage IME183, isolated from hospital sewage, exhibited lytic activity against K. pneumoniae of capsular type K2. Transmission electron microscopy revealed that phage IME183 has a head with a diameter of 50 nm and a short tail. Its genome is 41,384 bp in length with a GC content of 52.92%. It is predicted to contain 50 open reading frames (ORFs). The results of evolutionary analysis suggest that phage IME183 should be considered a member of a new species in the genus Przondovirus.

Impact of mutagenesis and lateral gene transfer processes in bacterial susceptibility to phage in food biocontrol and phage therapy

Introduction

The emergence of resistance and interference mechanisms to phage infection can hinder the success of bacteriophage-based applications, but the significance of these mechanisms in phage therapy has not been determined. This work studies the emergence of Salmonella isolates with reduced susceptibility to a cocktail of three phages under three scenarios: i) Salmonella cultures (LAB), ii) biocontrol of cooked ham slices as a model of food safety (FOOD), and iii) oral phage therapy in broilers (PT).

Methods

S. Typhimurium ATCC 14028 RifR variants with reduced phage susceptibility were isolated from the three scenarios and conventional and molecular microbiology techniques were applied to study them.

Results and discussion

In LAB, 92% of Salmonella isolates lost susceptibility to all three phages 24 h after phage infection. This percentage was lower in FOOD, with 4.3% of isolates not susceptible to at least two of the three phages after seven days at 4°C following phage treatment. In PT, 9.7% and 3.3 % of isolates from untreated and treated broilers, respectively, displayed some mechanism of interference with the life cycle of some of the phages. In LAB and FOOD scenarios, resistant variants carrying mutations in rfc and rfaJ genes involved in lipopolysaccharide synthesis (phage receptor) were identified. However, in PT, the significant decrease of EOP, ECOI, and burst size observed in isolates was prompted by lateral gene transfer of large IncI1 plasmids, which may encode phage defense mechanisms. These data indicate that the acquisition of specific conjugative plasmids has a stronger impact than mutagenesis on the emergence of reduced phage-susceptibility bacteria in certain environments. In spite of this, neither mechanism seems to significantly impair the success of Salmonella biocontrol and oral phage therapy.

The Biotechnological Application of Bacteriophages: What to Do and Where to Go in the Middle of the Post-Antibiotic Era

Amid the escalating challenges of antibiotic resistance, bacterial infections have emerged as a global threat. Bacteriophages (phages), viral entities capable of selectively infecting bacteria, are gaining momentum as promising alternatives to traditional antibiotics. Their distinctive attributes, including host specificity, inherent self-amplification, and potential synergy with antibiotics, render them compelling candidates. Phage engineering, a burgeoning discipline, involves the strategic modification of bacteriophages to enhance their therapeutic potential and broaden their applications. The integration of CRISPR-Cas systems facilitates precise genetic modifications, enabling phages to serve as carriers of functional genes/proteins, thereby enhancing diagnostics, drug delivery, and therapy. Phage engineering holds promise in transforming precision medicine, addressing antibiotic resistance, and advancing diverse applications. Emphasizing the profound therapeutic potential of phages, this review underscores their pivotal role in combatting bacterial diseases and highlights their significance in the post-antibiotic era.

Automating Predictive Phage Therapy Pharmacology

Viruses that infect as well as often kill bacteria are called bacteriophages, or phages. Because of their ability to act bactericidally, phages increasingly are being employed clinically as antibacterial agents, an infection-fighting strategy that has been in practice now for over one hundred years. As with antibacterial agents generally, the development as well as practice of this phage therapy can be aided via the application of various quantitative frameworks. Therefore, reviewed here are considerations of phage multiplicity of infection, bacterial likelihood of becoming adsorbed as a function of phage titers, bacterial susceptibility to phages also as a function of phage titers, and the use of Poisson distributions to predict phage impacts on bacteria. Considered in addition is the use of simulations that can take into account both phage and bacterial replication. These various approaches can be automated, i.e., by employing a number of online-available apps provided by the author, the use of which this review emphasizes. In short, the practice of phage therapy can be aided by various mathematical approaches whose implementation can be eased via online automation.

Refractory Pseudomonas aeruginosa infections treated with phage PASA16: A compassionate use case series

BACKGROUND

A growing number of compassionate phage therapy cases were reported in the last decade, with a limited number of clinical trials conducted and few unsuccessful clinical trials reported. There is only a little evidence on the role of phages in refractory infections. Our objective here was to present the largest compassionate-use single-organism/phage case series in 16 patients with non-resolving Pseudomonas aeruginosa infections.

METHODS

We summarized clinical phage microbiology susceptibility data, administration protocol, clinical data, and outcomes of all cases treated with PASA16 phage. In all intravenous phage administrations, PASA16 phage was manufactured and provided pro bono by Adaptive Phage Therapeutics. PASA16 was administered intravenously, locally to infection site, or by topical use to 16 patients, with data available for 15 patients, mainly with osteoarticular and foreign-device-associated infections.

FINDINGS

A few minor side effects were noted, including elevated liver function enzymes and a transient reduction in white blood cell count. Good clinical outcome was documented in 13 out of 15 patients (86.6%). Two clinical failures were reported. The minimum therapy duration was 8 days with a once- to twice-daily regimen.

CONCLUSIONS

PASA16 with antibiotics was found to be relatively successful in patients for whom traditional treatment approaches have failed previously. Such pre-phase-1 cohorts can outline potential clinical protocols and facilitate the design of future trials.

FUNDING

The study was funded in part by The Israeli Science Foundation IPMP (ISF_1349/20), Rosetrees Trust (A2232), United States-Israel Binational Science Foundation (2017123), and the Milgrom Family Support Program.

Isolation, characterization, and genome analysis of a broad host range Salmonella phage vB_SenS_TUMS_E4: a candidate bacteriophage for biocontrol

Salmonella enteritidis is one of the most important foodborne pathogens that cause numerous outbreaks worldwide. Some strains of Salmonella have become progressively resistant to antibiotics, so they could represent a critical threat to public health and have led to the use of alternative therapeutic approaches like phage therapy. In this study, a lytic phage, vB_SenS_TUMS_E4 (E4), was isolated from poultry effluent and characterized to evaluate its potential and efficacy for bio-controlling S. enteritidis in foods. Transmission electron microscopy revealed that E4 has a siphovirus morphotype, with an isometric head and non-contractile tail. Determining the host range showed that this phage can effectively infect different motile as well as non-motile Salmonella enterica serovars. The biological characteristics of E4 showed that it has a short latent period of about 15 min and a large burst size of 287 PFU/cell, and is also significantly stable in a broad range of pHs and temperatures. The E4 whole genome contains 43,018 bp and encodes 60 coding sequences (CDSs) but no tRNA genes. Bioinformatics analysis revealed that the genome of E4 lacks any genes related to lysogeny behavior, antibiotic resistance, toxins, or virulence factors. The efficacy of phage E4 as a bio-control agent was assessed in various foodstuffs inoculated with S. enteritidis at 4°C and 25°C, and the resulting data indicated that it could eradicate S. enteritidis after a very short time of 15 min. The findings of the present study showed that E4 is a hopeful candidate as a bio-control agent against S. enteritidis and has the potential to be used in various foodstuffs.

Comparative analysis of effectiveness for phage cocktail development against multiple Salmonella serovars and its biofilm control activity

Foodborne diseases are a major challenge in the global food industry, especially those caused by multidrug-resistant (MDR) bacteria. Bacteria capable of biofilm formation, in addition to MDR strains, reduce the treatment efficacy, posing a significant threat to bacterial control. Bacteriophages, which are viruses that infect and kill bacteria, are considered a promising alternative in combating MDR bacteria, both in human medicine and animal production. Phage cocktails, comprising multiple phages, are commonly employed to broaden the host range and prevent or delay the development of phage resistance. There are numerous techniques and protocols available to evaluate the lytic activity of bacteriophages, with the most commonly used methods being Spot Test Assays, Efficiency of Plating (EOP), and infection assays in liquid culture. However, there is currently no standardization for which analyses should be employed and the possible differences among them in order to precisely determine the host range of phages and the composition of a cocktail. A preliminary selection using the Spot Test Assay resulted in four phages for subsequent evaluation against a panel of 36 Salmonella isolates of numerous serovars. Comparing EOP and infection assays in liquid culture revealed that EOP could underestimate the lytic activity of phages, directly influencing phage cocktail development. Moreover, the phage cocktail containing the four selected phages was able to control or remove biofilms formed by 66% (23/35) of the isolates, including those exhibiting low susceptibility to phages, according to EOP. Phages were characterized genomically, revealing the absence of genes associated with antibiotic resistance, virulence factors, or integrases. According to confocal laser scanning microscopy analysis, the biofilm maturation of one Salmonella isolate, which exhibited high susceptibility to phages in liquid culture and 96-well plates biofilm viability assays but had low values for EOP, was found to be inhibited and controlled by the phage cocktail. These observations indicate that phages could control and remove Salmonella biofilms throughout their growth and maturation process, despite their low EOP values. Moreover, using infection assays in liquid culture enables a more precise study of phage interactions for cocktail design timelessly and effortlessly. Hence, integrating strategies and techniques to comprehensively assess the host range and lytic activity of bacteriophages under different conditions can demonstrate more accurately the antibacterial potential of phage cocktails.

A Bacteriophage-Loaded Microparticle Laden Topical Gel for the Treatment of Multidrug-Resistant Biofilm-Mediated Burn Wound Infection

Klebsiella pneumoniae is regarded as one of the most profound bacteria isolated from the debilitating injuries caused by burn wounds. In addition, the multidrug resistance (MDR) and biofilm formation make treating burn patients with clinically available antibiotics difficult. Bacteriophage therapy has been proven an effective alternative against biofilm-mediated wound infections caused by MDR bacterial strains. In the current study, the bacteriophage (BPKPФ1) against MDR Klebsiella pneumoniae was isolated and loaded into the chitosan microparticles (CHMPs), which was later incorporated into the Sepineo P 600 to convert into a gel (BPKPФ1-CHMP-gel). BPKPФ1 was characterized for lytic profile, morphological class, and burst size, which revealed that the BPKPФ1 belongs to the family Siphoviridae. Moreover, BPKPФ1 exhibited a narrow host range with 128 PFU/host cell of burst size. The BPKPФ1-loaded CHMPs showed an average particle size of  1.96 ± 0.51 μm, zeta potential 32.16 ± 0.41 mV, and entrapment efficiency in the range of 82.44 ± 1.31%. Further, the in vitro antibacterial and antibiofilm effectiveness of BPKPФ1-CHMPs-gel were examined. The in vivo potential of the BPKPФ1-CHMPs-gel was assessed using a rat model with MDR Klebsiella pneumoniae infected burn wound, which exhibited improved wound contraction (89.22 ± 0.48%) in 28 days with reduced inflammation, in comparison with different controls. Data in hand suggest the potential of bacteriophage therapy to be developed as personalized therapy in case of difficult-to-treat bacterial infections.

Bacteriophage cocktail application for Campylobacter mitigation - from in vitro to in vivo

BACKGROUND

Effective strategies are urgently needed to control Campylobacteriosis, one of the most important foodborne gastrointestinal diseases worldwide. Administering bacteriophages (phages) is under evaluation as a possible intervention strategy in primary poultry production to reduce the public health risk of human infection. A major challenge is the translation of results from small-scale animal studies to large broiler flocks. In this study, the in vitro lytic activity of 18 Campylobacter-specific group II phages and 19 group III phages were examined singly, and in different combinations from the same group and from both groups using a planktonic killing assay. Based on these results, a combination of phage NCTC 12,673 (group III) and vB_CcM-LmqsCPL1/1 (group II) was selected for in vivo application in a seeder bird model to study its effectiveness under conditions as close as possible to field conditions. One hundred eighty Ross 308 broiler chickens were divided into a control and a treatment group. Ten days post hatch, seeder birds were orally inoculated with the C. jejuni target strain. Phages were administered via drinking water at a total concentration of 107 PFU/mL four, three, and two days before necropsy.

RESULTS

Combining group II and group III phages resulted in significantly higher in vitro growth inhibition against the C. jejuni target strain BfR-CA-14,430 than single application or combinations of phages from the same group. The results of the animal trial showed that the application of the two phages significantly reduced Campylobacter counts in cloacal swabs. At necropsy, Campylobacter counts in colonic content of the treatment group were significantly reduced by 2 log10 units compared to the control group.

CONCLUSIONS

We demonstrated that combining phages of groups II and III results in significantly increased lytic activities. The in vitro results were successfully translated into practical application in a study design close to field conditions, providing new data to apply phages in conventional broiler flocks in the future. Phage application reduced the fecal Campylobacter excretion and Campylobacter concentrations in the colon of broilers.

Isolation of a bacteriophage targeting Pseudomonas aeruginosa and exhibits a promising in vivo efficacy

Pseudomonas aeruginosa is an important pathogen that causes serious infections. Bacterial biofilms are highly resistant and render bacterial treatment very difficult, therefore necessitates alternative antibacterial strategies. Phage therapy has been recently regarded as a potential therapeutic option for treatment of bacterial infections. In the current study, a novel podovirus vB_PaeP_PS28 has been isolated from sewage with higher lytic activity against P. aeruginosa. Isolated phage exhibits a short latent period, large burst size and higher stability over a wide range of temperatures and pH. The genome of vB_PaeP_PS28 consists of 72,283 bp circular double-stranded DNA, with G + C content of 54.75%. The phage genome contains 94 open reading frames (ORFs); 32 for known functional proteins and 62 for hypothetical proteins and no tRNA genes. The phage vB_PaeP_PS28 effectively inhibited the growth of P. aeruginosa planktonic cells and displayed a higher biofilm degrading capability. Moreover, therapeutic efficacy of isolated phage was evaluated in vivo using mice infection model. Interestingly, survival of mice infected with P. aeruginosa was significantly enhanced upon treatment with vB_PaeP_PS28. Furthermore, the bacterial load in liver and kidney isolated from mice infected with P. aeruginosa and treated with phage markedly decreased as compared with phage-untreated P. aeruginosa-infected mice. These findings support the efficacy of isolated phage vB_PaeP_PS28 in reducing P. aeruginosa colonization and pathogenesis in host. Importantly, the isolated phage vB_PaeP_PS28 could be applied alone or as combination therapy with other lytic phages as phage cocktail therapy or with antibiotics to limit infections caused by P. aeruginosa.

Molecular Characterization of Salmonella Phage Wara Isolated from River Water in Brazil

Antimicrobial resistance is increasing despite new treatments being employed, so novel strategies are required to ensure that bacterial infections remain treatable. Bacteriophages (phages; bacteria viruses) have the potential to be used as natural antimicrobial methods to control bacterial pathogens such as Salmonella spp. A Salmonella phage, Wara, was isolated from environmental water samples at the Subaé River Basin, Salvador de Bahia, Brazil. The basin has environmental impacts in its main watercourses arising from the dumping of domestic and industrial effluents and agricultural and anthropological activities. The phage genome sequence was determined by Oxford Nanopore Technologies (ONT) MinION and Illumina HiSeq sequencing, and assembly was carried out by Racon (MinION) and Unicycler (Illumina, Illumina + MinION). The genome was annotated and compared to other Salmonella phages using various bioinformatics approaches. MinION DNA sequencing combined with Racon assembly gave the best complete genome sequence. Phylogenetic analysis revealed that Wara is a member of the Tequintavirus genus. A lack of lysogeny genes, antimicrobial resistance, and virulence genes indicated that Wara has therapeutic and biocontrol potential against Salmonella species in healthcare and agriculture.

A systematic review of the use of bacteriophages for in vitro biofilm control

Bacteriophages (phages) are very promising biological agents for the prevention and control of bacterial biofilms. However, little is known about the parameters that can influence the efficacy of phages on biofilms. This systematic review provides a summary and analysis of the published data about the use of phages to control pre-formed biofilms in vitro, suggesting recommendations for future experiments in this area. A total of 68 articles, containing data on 605 experiments addressing the efficacy of phages to control biofilms in vitro were included, after a search conducted in Web of Science, Embase, and Medline (PubMed). The data collected from each experiment included information about biofilm growth conditions, phage characteristics, treatment conditions and biofilm reduction. In most cases, biofilms were formed in the surface of microtiter plates (82.5%); the median time for biofilm formation was 24 h, as is the median treatment duration. Quantification of biofilm biomass (52.6%), viable cells (25.5%) and metabolic activity (17.9%) were the most common biofilm assessment methods. Correlation analysis revealed that some phage parameters can influence the treatment outcome: higher phage concentrations were strongly associated with improved biofilm control, leading to higher levels of biofilm reduction, and phages with higher burst sizes and shorter latent periods seem to be the best candidates to control biofilms in vitro. However, the great variability of the methodologies used prompts the need for the development of standardized in vitro methodologies to characterize phage/biofilm interactions and to assess the efficacy of phages to control biofilms.

A Bacteriophage Microgel Effectively Treats the Multidrug-Resistant Acinetobacter baumannii Bacterial Infections in Burn Wounds

Multidrug-resistant (MDR) Acinetobacter baumannii (A. baumannii) is one of the major pathogens present in burn wound infections. Biofilm formation makes it further challenging to treat with clinically available antibiotics. In the current work, we isolated the A. baumannii-specific bacteriophages (BPABΦ1), loaded into the chitosan microparticles followed by dispersion in gel, and evaluated therapeutic efficacy against MDR A. baumannii clinical strains. Isolated BPABΦ1 were found to belong to the Corticoviridae family, with burst size 102.12 ± 2.65 PFUs per infected host cell. The BPABΦ1 loaded chitosan microparticles were evaluated for quality attributes viz. size, PDI, surface morphology, in vitro release, etc. The developed formulation exhibited excellent antibiofilm eradication potential in vitro and effective wound healing after topical application.

Characterization of Temperate LPS-Binding Bordetella avium Phages That Lack Superinfection Immunity

Bordetella avium causes a highly infectious upper respiratory tract disease in turkeys and other poultry with high economic losses. Considering the antimicrobial resistance crisis, bacteriophages (phages) may be an alternative approach for treating bacterial infections such as bordetellosis. Here, we describe seven B. avium phages, isolated from drinking water and feces from chicken and turkey farms. They showed strong bacteriolytic activity with a broad host range and used lipopolysaccharides (LPS) as a host receptor for their adsorption. All phages are myoviruses based on their structure observed by transmission electron microscopy. Genome sequence analyses revealed genome assembly sizes ranging from 39,087 to 43,144 bp. Their permutated genomes were organized colinearly, with a conserved module order, and were packed according to a predicted headful packing strategy. Notably, they contained genes encoding putative markers of lysogeny, indicative of temperate phages, despite their lytic phenotype. Further investigation revealed that the phages could indeed undergo a lysogenic life cycle with varying frequency. However, the lysogenic bacteria were still susceptible to superinfection with the same phages. This lack of stable superinfection immunity after lysogenization appears to be a characteristic feature of B. avium phages, which is favorable in terms of a potential therapeutic use of phages for the treatment of avian bordetellosis. IMPORTANCE To maintain the effectiveness of antibiotics over the long term, alternatives to treat infectious diseases are urgently needed. Therefore, phages have recently come back into focus as they can specifically infect and lyse bacteria and are naturally occurring. However, there is little information on phages that can infect pathogenic bacteria from animals, such as the causative agent of bordetellosis of poultry, B. avium. Therefore, in this study, B. avium phages were isolated and comprehensively characterized, including whole-genome analysis. Although phenotypically the phages were thought to undergo a lytic cycle, we demonstrated that they undergo a lysogenic phase, but that infection does not confer stable host superinfection immunity. These findings provide important information that could be relevant for potential biocontrol of avian bordetellosis by using phage therapy.

Isolation and characterization of bacteriophages from soil against food spoilage and foodborne pathogenic bacteria

Microbial food spoilage and foodborne disease are the main challenges in the food industry regarding food shelf life. Current preservation methods are frequently associated with changes in organoleptic characteristics and loss of nutrients. For this reason, bacteriophage offers an alternative natural method as a biocontrol agent that can reduce bacterial contamination in food without altering the organoleptic properties. This study was conducted to isolate and characterize bacteriophage from soil to control food spoilage bacteria, such as Bacillus cereus and Bacillus subtilis, and foodborne pathogenic bacteria, such as enterotoxigenic Escherichia coli (ETEC) and enterohemorrhagic E. coli (EHEC). Isolation was done by agar overlay assay method, and phages BC-S1, BS-S2, ETEC-S3, and EHEC-S4 were recovered. The host range of all isolated phages tended to be narrow and had high specificity towards the specific bacteria. The phage efficiency were measured where ETEC-S3 showed no effectivity against B. cereus and EHEC-S4 showed low efficiency against Enteropathogenic E. coli (EPEC). Morphology analysis was conducted for phage BC-S1 and ETEC-S3 with Transmission Electron Microscopy (TEM), and it is shown to belong to the Caudovirales order. Phages BC-S1 and BS-S2 significantly reduced the host bacteria when applied to the cooked rice and pasteurized milk samples with miMOI of 0.1. While phage ETEC-S3 at miMOI of 0.001 and phage EHEC-S4 at miMOI of 1 also showed a significant reduction when applied to chicken meat and lettuce samples at storage temperatures of 4 °C and 28 °C. The highest bacterial reduction of 100% was shown by phage BC-S1 on pasteurized milk samples and reduction up to 96.06% by phage ETEC-S3 on chicken meat samples at 28 °C incubation.

The host phylogeny determines viral infectivity and replication across Staphylococcus host species

Virus host shifts, where a virus transmits to and infects a novel host species, are a major source of emerging infectious disease. Genetic similarity between eukaryotic host species has been shown to be an important determinant of the outcome of virus host shifts, but it is unclear if this is the case for prokaryotes where anti-virus defences can be transmitted by horizontal gene transfer and evolve rapidly. Here, we measure the susceptibility of 64 strains of Staphylococcaceae bacteria (48 strains of Staphylococcus aureus and 16 non-S. aureus species spanning 2 genera) to the bacteriophage ISP, which is currently under investigation for use in phage therapy. Using three methods-plaque assays, optical density (OD) assays, and quantitative (q)PCR-we find that the host phylogeny explains a large proportion of the variation in susceptibility to ISP across the host panel. These patterns were consistent in models of only S. aureus strains and models with a single representative from each Staphylococcaceae species, suggesting that these phylogenetic effects are conserved both within and among host species. We find positive correlations between susceptibility assessed using OD and qPCR and variable correlations between plaque assays and either OD or qPCR, suggesting that plaque assays alone may be inadequate to assess host range. Furthermore, we demonstrate that the phylogenetic relationships between bacterial hosts can generally be used to predict the susceptibility of bacterial strains to phage infection when the susceptibility of closely related hosts is known, although this approach produced large prediction errors in multiple strains where phylogeny was uninformative. Together, our results demonstrate the ability of bacterial host evolutionary relatedness to explain differences in susceptibility to phage infection, with implications for the development of ISP both as a phage therapy treatment and as an experimental system for the study of virus host shifts.

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.

An Edible Biopolymeric Microcapsular Wrapping Integrating Lytic Bacteriophage Particles for Salmonella enterica: Potential for Integration into Poultry Feed

This research work aimed at developing an edible biopolymeric microcapsular wrapping (EBMW) integrating lytic bacteriophage particles for Salmonella enterica, with potential application in poultry feed for biocontrol of that pathogen. This pathogen is known as one of the main microorganisms responsible for contamination in the food industry and in foodstuff. The current techniques for decontamination and pathogen control in the food industry can be very expensive, not very selective, and even outdated, such as the use of broad-spectrum antibiotics that end up selecting resistant bacteria. Hence, there is a need for new technologies for pathogen biocontrol. In this context, bacteriophage-based biocontrol appears as a potential alternative. As a cocktail, both phages were able to significantly reduce the bacterial load after 12 h of treatment, at either multiplicity of infection (MOI) 1 and 10, by 84.3% and 87.6%, respectively. Entrapment of the phage virions within the EBMW matrix did not exert any deleterious effect upon their lytic activity. The results obtained showed high promise for integration in poultry feed aiming at controlling Salmonella enterica, since the edible biopolymeric microcapsular wrapping integrating lytic bacteriophage particles developed was successful in maintaining lytic phage viability while fully stabilizing the phage particles.

Isolation, Characterization, and Comparative Genomic Analysis of Bacteriophage Ec_MI-02 from Pigeon Feces Infecting Escherichia coli O157:H7

The most significant serotype of Shiga-toxigenic Escherichia coli that causes foodborne illnesses is Escherichia coli O157:H7. Elimination of E. coli O157:H7 during food processing and storage is a possible solution. Bacteriophages have a significant impact on bacterial populations in nature due to their ability to lyse their bacterial host. In the current study, a virulent bacteriophage, Ec_MI-02, was isolated from the feces of a wild pigeon in the United Arab Emirates (UAE) for potential future use as a bio-preservative or in phage therapy. Using a spot test and an efficiency of plating analysis, Ec_MI-02 was found to infect in addition to the propagation host, E. coli O157:H7 NCTC 12900, five different serotypes of E. coli O157:H7 (three clinical samples from infected patients, one from contaminated green salad, and one from contaminated ground beef). Based on morphology and genome analysis, Ec_MI-02 belongs to the genus Tequatrovirus under the order Caudovirales. The adsorption rate constant (K) of Ec_MI-02 was found to be 1.55 × 10^-8 mL/min. The latent period was 50 min with a burst size of almost 10 plaque forming units (pfu)/host cell in the one-step growth curve when the phage Ec_MI-02 was cultivated using the propagation host E. coli O157:H7 NCTC 12900. Ec_MI-02 was found to be stable at a wide range of pH, temperature, and commonly used laboratory disinfectants. Its genome is 165,454 bp long with a GC content of 35.5% and encodes 266 protein coding genes. Ec_MI-02 has genes encoding for rI, rII, and rIII lysis inhibition proteins, which supports the observation of delayed lysis in the one-step growth curve. The current study provides additional evidence that wild birds could also be a good natural reservoir for bacteriophages that do not carry antibiotic resistance genes and could be good candidates for phage therapy. In addition, studying the genetic makeup of bacteriophages that infect human pathogens is crucial for ensuring their safe usage in the food industry.

Morphological, biological, and genomic characterization of Klebsiella pneumoniae phage vB_Kpn_ZC2

BACKGROUND

Bacteriophages (phages) are one of the most promising alternatives to traditional antibiotic therapies, especially against multidrug-resistant bacteria. Klebsiella pneumoniae is considered to be an opportunistic pathogen that can cause life-threatening infections. Thus, this study aims at the characterization of a novel isolated phage vB_Kpn_ZC2 (ZCKP2, for short).

METHODS

The phage ZCKP2 was isolated from sewage water by using the clinical isolate KP/08 as a host strain. The isolated bacteriophage was purified and amplified, followed by testing of its molecular weight using Pulse-Field Gel Electrophoresis (PFGE), transmission electron microscopy, antibacterial activity against a panel of other Klebsiella pneumoniae hosts, stability studies, and whole genome sequencing.

RESULTS

Phage ZCKP2 belongs morphologically to siphoviruses as indicated from the Transmission Electron Microscopy microgram. The Pulsed Field Gel Electrophoresis and the phage sequencing estimated the phage genome size of 48.2 kbp. Moreover, the absence of lysogeny-related genes, antibiotic resistance genes, and virulence genes in the annotated genome suggests that phage ZCKP2 is safe for therapeutic use. Genome-based taxonomic analysis indicates that phage ZCKP2 represents a new family that has not been formally rated yet. In addition, phage ZCKP2 preserved high stability at different temperatures and pH values (-20 - 70 °C and pH 4 - 9). For the antibacterial activity, phage ZCKP2 maintained consistent clear zones on KP/08 bacteria along with other hosts, in addition to effective bacterial killing over time at different MOIs (0.1, 1, and 10). Also, the genome annotation predicted antibacterial lytic enzymes. Furthermore, the topology of class II holins was predicted in some putative proteins with dual transmembrane domains that contribute significantly to antibacterial activity. Phage ZCKP2 characterization demonstrates safety and efficiency against multidrug-resistant K. pneumoniae, hence ZCKP2 is a good candidate for further in vivo and phage therapy clinical applications.

Application of a novel lytic Jerseyvirus phage LPSent1 for the biological control of the multidrug-resistant Salmonella Enteritidis in foods

Non-typhoidal Salmonella is the tremendously predominant source of acquired foodborne infection in humans, causing salmonellosis which is a global threat to the healthcare system. This threat is even worse when it is combined with the incidence of multidrug-resistant Salmonella strains. Bacteriophage therapy has been proposed as a promising potential candidate to control a diversity of foodborne infective bacteria. The objective of this study designed to isolate and characterize lytic phages infecting zoonotic multi-drug resistant and strong biofilm producer Salmonella enterica serovar Enteritidis EG.SmE1 and then apply the isolated phage/s as a biocontrol agent against infections in ready-to-eat food articles including milk, water, apple juice, and chicken breasts. One lytic phage (LPSent1) was selected based on its robust and stable lytic activity. Phage LPSent1 belonged to the genus Jerseyvirus within the Jerseyvirinae subfamily. The lysis time of phage LPSent1 was 60 min with a latent period of 30 min and each infected cell burst about 112 plaque-forming units. Phage LPSent1 showed a narrow host range. Furthermore, the LPSent1 genome did not encode any virulence or lysogenic genes. In addition, phage LPSent1 had wide pH tolerance, prolonged thermal stability, and was stable in food articles lacking its susceptible host for 48 h. In vitro applications of phage LPSent1 inhibited free planktonic cells and biofilms of Salmonella Enteritidis EG.SmE1 with a lower occurrence to form phage-resistant bacterial mutants which suggests promising applications on food articles. Application of phage LPSent1 at multiplicities of infections of 100 or 1000 showed significant inhibition in the bacterial count of Salmonella Enteritidis EG.SmE1 by 5 log10/sample in milk, water, apple juice, and chicken breasts at either 4°C or 25°C. Accordingly, taken together these findings establish phage LPSent1 as an effective, promising candidate for the biocontrol of MDR Salmonella Enteritidis in ready-to-eat food.

Combine thermal processing with polyvalent phage LPEK22 to prevent the Escherichia coli and Salmonella enterica contamination in food

Thermal processing is the most frequently used method to destruct bacteria in food processing. However, insufficient thermal processing may lead to the outbreak of foodborne illness. This study combined thermal processing with thermostable phage to prevent food contamination. The thermostable phages were screened which can retain activity at 70 °C for 1 h. Among them, the polyvalent phage LPEK22 was obtained to lyse Escherichia coli and Salmonella enterica, especially several multi-drug resistant bacteria. In milk (liquid food matrix), LPEK22 significantly reduced the E. coli by 5.00 ± 0.18 log₁₀ CFU/mL and S. enterica by 4.20 ± 0.23 log₁₀ CFU/mL after thermal processing at 63 °C for 30 min. For beef sausage (solid food matrix), LPEK22 significantly reduced the E. coli by 2.34 ± 0.17 log₁₀ CFU/cm² and S. enterica by 1.54 ± 0.13 log₁₀ CFU/cm² after thermal processing at 66 °C for 90 s. Genome analysis revealed that LPEK22 was a novel phage with a unique tail spike protein belonging to the family of Ackermannviridae. LPEK22 did not contain lysogenic, drug-resistant, and virulent genes that may compromise the safety of food application. These results determined that LPEK22, a novel polyvalent Ackermannviridae phage, could combine with thermal processing to prevent drug-resistant E. coli and S. enterica both in vitro and in foods.