Phage Host Range Research Articles

Phage Adsorption to Gram-Positive Bacteria.

The phage life cycle is a multi-stage process initiated by the recognition and attachment of the virus to its bacterial host. This adsorption step depends on the specific interaction between bacterial structures acting as receptors and viral proteins called Receptor Binding Proteins (RBP). The adsorption process is essential as it is the first determinant of phage host range and a sine qua non condition for the subsequent conduct of the life cycle. In phages belonging to the Caudoviricetes class, the capsid is attached to a tail, which is the central player in the adsorption as it comprises the RBP and accessory proteins facilitating phage binding and cell wall penetration prior to genome injection. The nature of the viral proteins involved in host adhesion not only depends on the phage morphology (i.e., myovirus, siphovirus, or podovirus) but also the targeted host. Here, we give an overview of the adsorption process and compile the available information on the type of receptors that can be recognized and the viral proteins taking part in the process, with the primary focus on phages infecting Gram-positive bacteria.

Emerging investigator series: the role of phage lifestyle in wastewater microbial community structures and functions: insights into diverse microbial environments

Harnessing phage for biological treatment is of growing interest, but an improved understanding of phage diversity, host range, lifestyle, molecular signaling, and genetic potential are needed for microbial community control.

Selection and characterization of bacteriophages specific to Salmonella Choleraesuis in swine.

Salmonella Choleraesuis is the most common serotype that causes salmonellosis in swine. Recently, the use of bacteriophages as a potential biocontrol strategy has increased. Therefore, this study aimed to isolate and characterize bacteriophages specific to S. Choleraesuis associated with swine infection and to evaluate the efficacy of individual phages and a phage cocktail against S. Choleraesuis strains in simulated intestinal fluid (SIF). Three strains of S. Choleraesuis isolated from pig intestines served as host strains for phage isolation. The other 10 Salmonella serovars were also used for the phage host range test. The antibiotic susceptibility of the bacterial strains was investigated. Water samples from natural sources and drain liquid from slaughterhouses were collected for phage isolation. The isolated phages were characterized by determining the efficiency of plating against all Salmonella strains and the stability at a temperature range (4°C-65°C) and at low pH (2.5-4.0) in simulated gastric fluids (SGFs). Furthermore, morphology and genomic restriction analyses were performed for phage classification phages. Finally, S. Choleraesuis reduction in the SIF by the selected individual phages and a phage cocktail was investigated. The antibiotic susceptibility results revealed that most Salmonella strains were sensitive to all tested drugs. Salmonella Choleraesuis KPS615 was multidrug-resistant, showing resistance to three antibiotics. Nine phages were isolated. Most of them could infect four Salmonella strains. Phages vB_SCh-RP5i3B and vB_SCh-RP61i4 showed high efficiency in infecting S. Choleraesuis and Salmonella Rissen. The phages were stable for 1 h at 4°C-45°C. However, their viability decreased when the temperature increased to 65°C. In addition, most phages remained viable at a low pH (pH 2.5-4.0) for 2 h in SGF. The efficiency of phage treatment against S. Choleraesuis in SIF showed that individual phages and a phage cocktail with three phages effectively reduced S. Choleraesuis in SIF. However, the phage cocktails were more effective than the individual phages. These results suggest that the newly isolated phages could be promising biocontrol agents against S. Choleraesuis infection in pigs and could be orally administered. However, further in vivo studies should be conducted.

Rapid hydrogel-based phage susceptibility test for pathogenic bacteria.

Phage therapy is one alternative to cure infections caused by antibiotic resistant bacteria. Due to the narrow host range of phages, hundreds to thousands of phages are required to cover the diversity of bacterial pathogens. In personalized phage therapy, fast selection of the phages for individual patients is essential for successful therapy. The aims of this study were to set up a rapid hydrogel-based liquid phage susceptibility assay (PST) for the selection of phages for therapeutic use and to establish a "ready-to-screen" plate concept, where phages are readily stored in hydrogel as small droplets in microtiter plate wells. We first tested four commercially available hydrogels (GrowDex, Askina, Purilon, and Intrasite) for their suitability as phage matrices in PSTs with four phages, two of which infecting Escherichia coli and two Staphylococcus aureus. Of these four hydrogels, GrowDex was the best matrix for PST, as it did not inhibit bacterial growth, released phages quickly when mixed with bacterial culture, and maintained phage viability well. We then optimized the assay for both optical density and microscopy readers using GrowDex as matrix with 23 bacterial strains representing 10 different species and 23 phages possessing different morphologies and genome sizes. When the bacterial growth was monitored by microscopy reader, the PST was executed in just 3 hours, and there was no need for overnight culturing bacterial cells prior to the assay, whereas using optical density reader, bacteria had to be pre-cultured overnight, and the assay time was five hours. Finally, we evaluated the effect of three different chemical stabilizers (trehalose, hyaluronic acid, and gelatin) in a six-month stability assay with six model phages. These phages assay behaved very differently in respect to the chemical stabilizers, and there was not a single stabilizer suitable for all phages. However, when gelatin (0.01%) or hyaluronic acid (0.2 mg/ml) was used as stabilizer, all tested phages were still considered as positives in PST after a six-month storage in 1ml volume. In "ready-to-screen" plates, the differences in phage stabilities were even more profound, varying from two to six months for the most and least stable phages, respectively.

Isolation and characterization of Klebsiella pneumoniae bacteriophages encoding polysaccharide depolymerases with rare capsule specificity

Bacterial infections caused by antibiotic resistant strains of Klebsiella pneumoniae are among the most dangerous threats for the world's public healthcare. Treatment with bacteriophages and/or their derivatives could become one of the alternative methods for therapy of infections caused by K. pneumoniae. The study was aimed to isolate from the environment and characterize the capsule-specific K. pneumoniae bacteriophages that are useful for therapy and possess the polysaccharide depolymerase genes. Bacteriophages were isolated from the river water samples by enrichment method. The host range of bacteriophages were assessed using the collection of 180 K. pneumoniae clinical strains. Bacteriophage whole genome sequencing was performed on the MiSeq platform (Illumina). Four new bacteriophages from different taxonomic groups were isolated and characterized during the study: vB_KpnM_NDO71 (Vequintavirinae family), vB_KpnS_MAG26fr (Casjensviridae family), vB_KpnS_MDA2066 (Ackermannviridae family), and vB_KpnS_PMM-G3 (Drexlerviridae family). Bacteriophages vB_KpnM_NDO71, vB_KpnS_MAG26fr, and vB_KpnS_PMM-G3 had a narrow lytic spectrum and lysed all strains with the capsular type of the host: KL45, KL19 or KL28, respectively. Bacteriophage vB_KpnS_MDA2066 showed lytic activity against strains with two different capsular types: KL19 and KL107. Bacteriophages were strictly virulent and contained no integrase genes, potentially dangerous toxin genes or antibiotic resistance determinants. This allows them to be used in therapeutic practice. Receptor-binding proteins represented by polysaccharide depolymerases were predicted for each bacteriophage.

Modeling the Directed Evolution of Broad Host Range Phages.

Background: The host ranges of individual phages tend to be narrow, yet many applications of phages would benefit from expanded host ranges. Empirical methods have been developed to direct the evolution of phages to attack new strains, but the methods have not been evaluated or compared for their consequences. In particular, how do different methods favor generalist (broad host range) phages over specialist phages? All methods involve exposing phages to two or more novel bacterial strains, but the methods differ in the order in which those hosts are presented through time: Parallel presentation, Sequential presentation, and Mixed presentation. Methods: We use a combination of simple analytical methods and numerical analyses to study the effect of these different protocols on the selection of generalist versus specialist phages. Results: The three presentation protocols have profoundly different consequences for the evolution of generalist versus specialist phages. Sequential presentation favors generalists almost to the exclusion of specialists, whereas Parallel presentation does the least so. However, other protocol attributes (the nature of dilution between transfers of phages to new cultures) also have effects on selection and phage maintenance. It is also noted that protocols can be designed to enhance recombination to augment evolution and to reduce stochastic loss of newly arisen mutants.

Isolation and identification of the broad-spectrum high-efficiency phage vB_SalP_LDW16 and its therapeutic application in chickens

BackgroundSalmonella infection in livestock and poultry causes salmonellosis, and is mainly treated using antibiotics. However, the misuse use of antibiotics often triggers the emergence of multi-drug-resistant Salmonella strains. Currently, Salmonella phages is safe and effective against Salmonella, serving as the best drug of choice. This study involved 16 Salmonella bacteriophages separated and purified from the sewage and the feces of the broiler farm. A phage, vB_SalP_LDW16, was selected based on the phage host range test. The phage vB_SalP_LDW16 was characterized by the double-layer plate method and transmission electron microscopy. Furthermore, the clinical therapeutic effect of phage vB_SalP_LDW16 was verified by using the pathogenic Salmonella Enteritidis in the SPF chicken model.ResultsThe phage vB_SalP_LDW16 with a wide host range was identified to the family Siphoviridae and the order Caudoviridae, possess a double-stranded DNA and can lyse 88% (22/25) of Salmonella strains stored in the laboratory. Analysis of the biological characteristics, in addition, revealed the optimal multiplicity of infection (MOI) of vB_SalP_LDW16 to be 0.01 and the phage titer to be up to 3 × 1014 PFU/mL. Meanwhile, the phage vB_SalP_LDW16 was found to have some temperature tolerance, while the titer decreases rapidly above 60 ℃, and a wide pH (i.e., 5–12) range as well as relative stability in pH tolerance. The latent period of phage was 10 min, the burst period was 60 min, and the burst size was 110 PFU/cell. Furthermore, gastric juice was also found to highly influence the activity of the phage. The clinical treatment experiments showed that phage vB_SalP_LDW16 was able to significantly reduce the bacterial load in the blood through phage treatment, thereby improving the pathological changes in the intestinal, liver, and heart damage, and promoting the growth and development of the chicken.ConclusionsThe phage vB_SalP_LDW16 is a highly lytic phage with a wide host range, which can be potentially used for preventing and treating chicken salmonellosis, as an alternative or complementary antibiotic treatment in livestock farming.

Understanding Bacteriophage Tail Fiber Interaction with Host Surface Receptor: The Key "Blueprint" for Reprogramming Phage Host Range.

Bacteriophages (phages), as natural antibacterial agents, are being rediscovered because of the growing threat of multi- and pan-drug-resistant bacterial pathogens globally. However, with an estimated 1031 phages on the planet, finding the right phage to recognize a specific bacterial host is like looking for a needle in a trillion haystacks. The host range of a phage is primarily determined by phage tail fibers (or spikes), which initially mediate reversible and specific recognition and adsorption by susceptible bacteria. Recent significant advances at single-molecule and atomic levels have begun to unravel the structural organization of tail fibers and underlying mechanisms of phage–host interactions. Here, we discuss the molecular mechanisms and models of the tail fibers of the well-characterized T4 phage’s interaction with host surface receptors. Structure–function knowledge of tail fibers will pave the way for reprogramming phage host range and will bring future benefits through more-effective phage therapy in medicine. Furthermore, the design strategies of tail fiber engineering are briefly summarized, including machine-learning-assisted engineering inspired by the increasingly enormous amount of phage genetic information.

Characterisation of broad-spectrum phiKZ like jumbo phage and its utilisation in controlling multidrug-resistant Pseudomonas aeruginosa isolates

The emergence of highly virulent multidrug-resistant P. aeruginosa has become increasingly evident among hospital-acquired infections and has raised the need for alternative therapies. Phage therapy can be one such alternative to antibiotic therapy to combat multidrug-resistant pathogenic bacteria, but this requires the availability of phages with a broad host range. In this study, isolation and molecular characterisation of P. aeruginosa specific phages were carried out. A total of 17 phages isolated showed different spectra of activity and efficiency of lysis against 82 isolates of P. aeruginosa obtained from clinical samples (n = 13), hospital effluent (n = 46) and fish processing plant effluent (n = 23). Antibiotic susceptibility test results revealed multi-drug resistance in 61 of the total 82 isolates. Three new jumbo lytic P. aeruginosa specific broad host range phages were isolated and characterised in this present study belonged to the family Myoviridae (order Caudovirales). The genetic analysis of ɸU5 revealed that phage has a genome size of 282.6 kbp with 373 putative open reading frames (ORFs), and its genetic architecture is similar to phiKZ like jumbo phages infecting P. aeruginosa. The bacteriophages isolated in this study had lytic ability against biofilm-forming and multidrug-resistant P. aeruginosa and could be candidates for further studies towards phage therapy.

The presence of plasmids in bacterial hosts alters phage isolation and infectivity

Antibiotic resistance genes are often carried by plasmids, which spread intra- and inter genera bacterial populations, and also play a critical role in bacteria conferring phage resistance. However, it remains unknown about the influence of plasmids present in bacterial hosts on phage isolation and subsequent infectivity. In this study, using both Escherichia coli and Pseudomonas putida bacteria containing different plasmids, eight phages were isolated and characterized in terms of phage morphology and host range analysis, in conjunction with DNA and protein sequencing. We found that plasmids can influence both the phage isolation process and phage infectivity. In particular, the isolated phages exhibited different phage plaquing infectivity towards the same bacterial species containing different plasmids. Furthermore, the presence of plasmids was found to alter the expression of bacteria membrane protein, which correlates with bacterial cell surface receptors recognized by phages, thus affecting phage isolation and infectivity. Given the diverse and ubiquitous nature of plasmids, our findings highlight the need to consider plasmids as factors that can influence both phage isolation and infectivity.

Expansion of the Plaquing Host Range and Improvement of the Absorption Rate of a T5-like Salmonella Phage by Altering the Long Tail Fibers.

The high host specificity of phages is a real challenge in the therapy applications of the individual phages. This study aimed to edit the long tail fiber proteins (pb1) of a T5-like phage to obtain the engineered phages with expanded plaquing host range. Two T5-like Salmonella phages with high genome sequence homology but different plaquing host ranges, narrow-host range phage vB STyj5-1 (STyj5-1) and wide-host range phage vB BD13 (BD13), were isolated and characterized. The pb1 parts of STyj5-1 were replaced by the corresponding part of BD13 using homologous recombination method to obtain the engineered phages. The alterations of the whole pb1 part or the N-terminal amino acids 1-400 of pb1 of STyj5-1 could expand their plaquing host ranges (from 20 strains to 30 strains) and improve their absorption rates (from 0.28-28.84% to 28.10-99.49%). Besides, the one-step growth curves of these engineered phages with modified pb1 parts were more similar to that of STyj5-1. The burst sizes of phages BD13, STyj5-1 and the engineered phages were 250, 236, 166, and 223 PFU per cell, respectively. The expanded plaquing host range and improved absorption rates of these engineered phages revealed that the pb1 part might be the primary determinant of the host specificities of some T5-like phages. IMPORTANCE Genetic editing can be used to change or expand the host range of phages and have been successfully applied in T2, T4 and other phages to obtain engineered phages. However, there are hardly any similar reports on T5-like phages due to that the determinant regions related to their host ranges have not been completely clarified and the editing of T5-like phages is more difficult compared to other phages. This study attempted and successfully expanded the host range of a narrow-host range T5-like phage (STyj5-1) by exchanging its whole pb1 part or the N-terminal 1-400aa of that part by a broad-host range phage (BD13). These demonstrated the pb1 part might be the primary determinant of the host specificities for some T5-like phages and provided an effective method of extension plaquing host range of these phages.

Isolation and genomic characterization of a novel Autographiviridae bacteriophage IME184 with lytic activity against Klebsiella pneumoniae

Klebsiella pneumoniae, a multidrug resistant bacterium that causes nosocomial infections including septicemia, pneumonia etc. Bacteriophages are potential antimicrobial agents for the treatment of antibiotic resistant bacteria. In this study, a novel bacteriophage IME184, was isolated from hospital sewage against clinical multi-drug resistant Klebsiella pneumoniae. Transmission electron microscopy and genomic characterization exhibited this phage belongs to the Molineuxvirinae genus, Autographiviridae family. Phage IME184 possessed a double-stranded DNA genome composed of 44,598 bp with a GC content of 50.3%. The phage genome encodes 57 open reading frames, out of 26 are hypothetical proteins while 31 had assigned putative functions. No tRNA, virulence related or antibiotic resistance genes were found in phage genome. Comparative genomic analysis showed that phage IME184 has 94% similarity with genomic sequence of Klebsiella phage K1-ULIP33 (MK380014.1). Multiplicity of infection, one step growth curve and host range of phage were also measured. According to findings, Phage IME184 is a promising biological agent that infects Klebsiella pneumoniae and can be used in future phage therapies.

Phage Therapy: Challenges and Opportunities

The development of antibiotic resistance in bacteria is a growing concern. This situation demands a search for antibiotic alternatives. Bacteriophages—natural viral predators of bacteria—are viewed as a possible alternative to treat bacterial infections. Many clinical trials today have not found phages effective as therapeutics. Some of the major challenges regarding usage of bacteriophage as a therapeutic have been: horizontal evolution of bacteria, limited host range of bacteriophage, removal of endotoxins in preparations, the technical feasibility of isolation, mode of administration, rapid clearance and immune rejection.These issues have been addressed in this review. Applications of genetic engineered phages and other remarkable non-human applications are also discussed.

Therapeutic effectiveness of bacteriophage in the treatment of pneumonia caused by NDM-4 producing in a mouse model

Exploration for an alternative to antibiotics to treat bacterial diseases is becoming more important due to the emergence of antibiotic resistance. Bacteriophage or phage has been used for the treatment of superficial infections. In this study, phage isolated from the environment was used as a therapeutic agent against NDM-producing causing respiratory disease in an experimental mouse model. The isolated phage was found to belong to the family based on morphology. For experiments, five groups of mice were used including infection-free, phage-only, bacteria-infected, and the other two groups infected with and treated either with an antibiotic, levofloxacin (50 mg/kg, twice a day intraperitoneally) or phage (3×10 PFU/mL). All the animals were observed for 72 hours for mortality, and the surviving mice were killed for analysis. In the infected group, pneumonia was developed after 48 hours, and 8/10 animals were dead after 72 hours. When pneumonia infected mice were treated with an antibiotic, levofloxacin all the animals survived but showed the signs of pneumonia, and there was up to 6 log CFU/g±0.82 reduction in the bacterial count. In phage treated group, all the animals survived at the end of 72 hours and all the animals were healthy with no signs of pneumonia. The experiment showed new insights into the biology of the broad host range of phage, demonstrating that phage has prospects for the treatment of pneumonia caused by the NDM-producing .

Formulation of a Novel Phage Cocktail against Vibrio cholerae O1

A number of 26 phages lytic for 26 isolates of V. cholerae O1, biotype El Tor, Serotype Inaba are isolated from sewage water. The phage isolates showed host range of 35-65% against V. cholerae O1 by spot lysis methods. The morphological properties of plaques formed on the top agarose are studied and showed that most virulent phages had larger diameter (in millimeter) with regular or irregular margin cut and clear plaque comparing with smaller diameter and turbid plaque for those less virulent phages. A total of 8 phages are selected for formulation the phage cocktail in order to extend the host-range of phages in cocktail collectively. The %inhibition assay for every single phage of the 8 phages selected for formulation of phage cocktail ranged from 0-75, whereas that of the 8 phages cocktail was 100%inhibition against all V. cholerae O1 isolates. The formulation of the 8 phages in a cocktail proved to an effective approach to achieve the broad host-range activity towards V. cholerae O1 isolates and made it possible to go forwards the animal model for further studies on phage therapy for animal model of cholera.

Genomic characterization of three bacteriophages targeting multidrug resistant clinical isolates of Escherichia, Klebsiella and Salmonella

Application of bacteriophages (phages) to treat complex multidrug-resistant bacterial infection is gaining traction because of its efficacy and universal availability. However, as phages are specific to their host, a diverse collection of locally isolated phage from various geographical locations is required to formulate a wide host range phage cocktail. Here, we report morphological and genomic features of three newly isolated phages from river water of the urban region in Kathmandu, Nepal, targeting three different bacteria (Escherichia coli, Klebsiella pneumoniae and Salmonella enterica.) from the Enterobacteriaceae family. Morphological identification and genome analysis indicated that two phages (Escherichia phage vB_EcoM_TU01 and Klebsiella phage vB_KpnP_TU02) were strictly lytic and free from integrases, virulence factors, toxins and known antimicrobial resistance genes, whereas Salmonella phage vB_SalS_TU03 was possibly a temperate phage. The genomic features of these phages indicate that natural phages are capable of lysing pathogenic bacteria and may have potential in bacterial biocontrol.

Isolation and Analysis of the Biological Characteristics of a Novel Bacteriophage vB_SauP_P992 Against Staphylococcus aureus

Background: Staphylococcus aureus is one of the most virulent pathogens inducing various diseases in humans and animals. Disturbingly, the degree and rate of drug resistance in this pathogen have sharply increased and have become a global concern. Objectives: This study analyzed the lytic activity and the biological characteristics of a mitomycin C-induced bacteriophage from S. aureus isolated and identified from hospital sewage to explore novel antibacterial therapeutic strategies for the clinical treatment of drug-resistant S. aureus, including urinary tract infections caused by MRSA strains. Methods: The new bacteriophage vB_SauP_P992, which can effectively lyse the MRSA strain, was successfully isolated and purified using the double agar plate method. In this regard, pH sensitivity, one-step growth curve, the optimal multiplicity of infection (MOI), thermo-sensitivity, phage host range, and the effects of organic reagents on phage activity were determined. Results: Electron microscopic results showed that the bacteriophage head was hexagonal with a non-contractile tail and could form a single, neatly-bordered plaque. Moreover, the optimal MOI was 0.1. The one-step growth curve showed a bacteriophage incubation period of about 20 min, a lysis period of 90 min, and a burst size of about 65.8 PFU per infected cell. The bacteriophage vB_SauP_P992 had acceptable thermal stability, pH stability, and resistance to physical and chemical factors, indicating a bacteriophage with no capsule. Conclusions: With an intense lytic activity and acceptable stability, this novel bacteriophage lays a solid foundation to enrich the bacteriophage library and better prevent and control drug-resistant S. aureus infections.

Broad host range bacteriophage, EscoHU1, infecting Escherichia coli O157:H7 and Salmonella enterica: Characterization, comparative genomics, and applications in food safety

Shiga toxin-producing Escherichia coli and Salmonella enterica are important pathogens worldwide. Bacteriophages can be effectively used to reduce the incidence of foodborne pathogens. The host recognition systems of phages are highly specific, with the host range of a common phage being limited to the species or strain level. Here, we characterized a novel broad-host-range phage, EscoHU1, that infects several bacterial species, including E. coli and S. enterica, and evaluated its antimicrobial potential to inhibit E. coli O157:H7 and S. Typhimurium growth in food systems. The adsorption of EscoHU1 on E. coli was faster than that on S. Typhimurium; however, the one-step growth curves of EscoHU1 in both species were similar. Genomic analysis of EscoHU1 revealed that this phage has long direct terminal repeats at both ends of the genome, and phylogenetic analysis of the terminase large subunit confirmed that EscoHU1 belongs to the genus Epseptimavirus. Comparative analysis of structural proteins indicated a diversity of proteins related to the host range (receptor-binding proteins and L-shaped tail fibers). Challenge tests using beef and milk demonstrated the antimicrobial effects of EscoHU1 in inhibiting the growth of E. coli O157:H7 and S. Typhimurium in the food system. However, the antimicrobial effect of EscoHU1 on S. Typhimurium was lower than that on E. coli O157:H7. These results suggest that the novel broad-host-range phage EscoHU1 may serve as an effective antimicrobial agent to reduce food poisoning caused by E. coli O157:H7 and S. Typhimurium.

Isolation and Characterization of a Lytic Vibriophage OY1 and Its Biocontrol Effects Against Vibrio spp.

Vibrio species are important pathogens of marine animals and aquaculture populations and some of them can cause serious infections in humans through consumption of contaminated seafood and aquaculture products. Lytic bacteriophages can potentially alleviate Vibrio contamination in the aquaculture organisms and in the processing of aquatic products and have gained significant scientific attention in recent years. In the present study, bacteriophages were isolated from sewage of local aquatic products markets and grown using Vibrio mimicus CICC 21613 as host cells. The lytic vibriophage OY1 belonging to the newly proposed family Autographiviridae and the genus Maculvirus was identified by observation under electron microscope and comparative genomic analysis. The phage OY1 showed lytic activity against 24 among 32 tested strains belonging to eight Vibrio species. The complete phage OY1 genome consists of a single circular double-stranded DNA of 43,479 bp with a total GC content of 49.27% and was predicted to encode 40 open reading frames (ORFs). To evaluate its potential against vibrios, the one-step growth curve, thermal and pH stability, host range, and lytic activity of the OY1 phage against Vibrio species were evaluated. The results showed that phage OY1 had a range of thermal and pH tolerance, and exhibited a significant inhibitory effect on the growth of tested Vibrio species. Bacterial growth in the fish muscle extract juice (FMEJ) inoculated with Vibrio mimicus CICC 21613, Vibrio parahaemolyticus CICC 21617, Vibrio alginolyticus VJ14, and the mixed bacterial culture was reduced by 2.65 log CFU/ml, 2.42 log CFU/ml, 1.93 log CFU/ml, and 2.01 log CFU/ml, respectively, by incubation with phage OY1 at 25°C for 36 h. Phage OY1 also showed a strong ability to prevent biofilm formation and destroy formed Vibrio species biofilms. These results indicate that phage OY1 is a potential biocontrol agent against Vibrio species in the aquaculture industry and in food safety control.

Isolation and Characterization of Lytic Bacteriophages from Wastewater against Listeria monocytogenes

Background and Aims: In the current study, two bacteriophages were isolated from the wastewater sources and characterized by lytic activity against the Listeria monocytogenes (L. monocytogenes) bacterium.
 Materials and Methods: 50 wastewater samples were collected from the disposal sites. The phages were isolated from the treated samples using the double agar overlay method with L. monocytogenes as the host bacterium. Plaque morphology, temperature, pH, titration of phage lysate, host range, and scanning electron microscopic morphology were used to characterize the isolated phages.
 Results: Bacteriophage was found in two samples taken from wastewater treatment plants. Phages were proliferated and released under optimal bacterial growth conditions at pH 7; 37 °C in 36-hour incubation. A 10:1 ratio of bacterial cells to phage produced the greatest lytic ability. The highest phage titrated under optimal conditions was estimated at 9×109 pfu/ml. The scanning electron microscopic image revealed a bacteriophage morphology corresponding to the head and tail group. The host range observations demonstrated that L. monocytogenes were unique to the isolated phage. The elimination of L. monocytogenes growth in milk and whey samples revealed that this bacteriophage targeted bacteria and resulted in a 75% reduction in bacterial contamination.
 Conclusion: The results suggest that the phages obtained from L. monocytogenes may be utilized to combat this pathogen in dairy, agri-food, wastes, and other associated infections.