Genome characterization of a novel vibriophage VpKK5 (Siphoviridae) specific to fish pathogenic strain of Vibrio parahaemolyticus

Lysin and Lytic Phages Reduce Vibrio Counts in Live Feed and Fish Larvae

Vibrio species are naturally found in estuarine and marine ecosystems, but are also recognized as significant human enteropathogens, often linked to seafood-related illnesses. In aquaculture settings, Vibrio poses a substantial risk of infectious diseases, resulting in considerable stock losses and prompting the use of antimicrobials. However, this practice contributes to the proliferation of antimicrobial-resistant (AMR) bacteria and resistance genes. Our investigation aimed to explore the potential of biological agents such as bacteriophage CH20 and endolysin LysVPp1 in reducing Vibrio bacterial loads in both rotifer and fish larvae. LysVPp1's lytic activity was assessed by measuring absorbance reduction against various pathogenic Vibrio strains. Phage CH20 exhibited a limited host range, affecting only Vibrio alginolyticus GV09, a highly pathogenic strain. Both CH20 and LysVPp1 were evaluated for their effectiveness in reducing Vibrio load in rotifers or fish larvae through short-setting bioassays. Our results demonstrated the significant lytic effect of endolysin LysVPp1 on strains of Vibrio alginolyticus, Vibrio parahaemolyticus, and Vibrio splendidus. Furthermore, we have showcased the feasibility of reducing the load of pathogenic Vibrio in live feed and fish larvae by using a non-antibiotic-based approach, such as lytic phage and endolysin LysVPp1, thus contributing to the progress of a sustainable aquaculture from a One Health perspective.

Isolation and characterization of a novel phage belonging to a new genus against Vibrio parahaemolyticus

BACKGROUND

Vibrio parahaemolyticus is a major foodborne pathogen that contaminates aquatic products and causes great economic losses to aquaculture. Because of the emergence of multidrug-resistant V. parahaemolyticus strains, bacteriophages are considered promising agents for their biocontrol as an alternative or supplement to antibiotics. In this study, a lytic vibriophage, vB_VpaM_R16F (R16F), infecting V. parahaemolyticus 1.1997^T was isolated, characterized and evaluated for its biocontrol potential.

METHODS

A vibriophage R16F was isolated from sewage from a seafood market with the double-layer agar method. R16F was studied by transmission electron microscopy, host range, sensitivity of phage particles to chloroform, one-step growth curve and lytic activity. The phage genome was sequenced and in-depth characterized, including phylogenetic and taxonomic analysis.

RESULTS

R16F belongs to the myovirus morphotype and infects V. parahaemolyticus, but not nine other Vibrio spp. As characterized by determining its host range, one-step growth curve, and lytic activity, phage R16F was found to highly effective in lysing host cells with a short latent period (< 10 min) and a small burst size (13 plaque-forming units). R16F has a linear double-stranded DNA with genome size 139,011 bp and a G + C content of 35.21%. Phylogenetic and intergenomic nucleotide sequence similarity analysis revealed that R16F is distinct from currently known vibriophages and belongs to a novel genus. Several genes (e.g., encoding ultraviolet damage endonuclease and endolysin) that may enhance environmental competitiveness were found in the genome of R16F, while no antibiotic resistance- or virulence factor-related gene was detected.

CONCLUSIONS

In consideration of its biological and genetic properties, this newly discovered phage R16F belongs to a novel genus and may be a potential alternate biocontrol agent.

Isolation, characterization, and complete genome sequence of vibrio phage KIT04, a novel lytic phage of the subfamily ermolyevavirinae

Vibrio phage KIT04 was isolated from muscle tissue samples collected from a local market in Vietnam. KIT04 is a lytic phage that is specific to Vibrio parahaemolyticus. The one-step growth curve determined the burst size and latent period of 0.01 multiplicity of infection KIT04 in V. parahaemolyticus as approximately 156 plaque-forming units/bacterium and 45 min, respectively. Vibrio phage KIT04 has an approximately 76.4 ± 4.5 nm diameter icosahedral head and a tail length of approximately 159.5 ± 16.6 nm long tail. KIT04 significantly reduced V. parahaemolyticus ATCC 17802 in vitro. Complete genome analysis showed that KIT04 had a 114,933 bp dsDNA genome with 40.24% G + C content and 160 open reading frames (ORFs). However, the phage genome contained 24 tRNAs and no lysogeny-related genes. Moreover, five of the 160 ORFs encoded unique hypothetical proteins, indicating that KIT04 is a novel phage. Genomic comparison indicated that KIT04 is closely related to the Vibrio phages pVp-1 and VPT02. Further, phylogenetic analysis of the major tail proteins and whole genome supported the KIT04 classification into the subfamily Ermolyevavirinae. Our study describes a new candidate phage that could be used as a bioagent for controlling Vibrio pathogens.

Role of Bacteriophages in the Evolution of Pathogenic Vibrios and Lessons for Phage Therapy

Viruses of bacteria, i.e., bacteriophages (or phages for short), were discovered over a century ago and have played a major role as a model system for the establishment of the fields of microbial genetics and molecular biology. Despite the relative simplicity of phages, microbiologists are continually discovering new aspects of their biology including mechanisms for battling host defenses. In turn, novel mechanisms of host defense against phages are being discovered at a rapid clip. A deeper understanding of the arms race between bacteria and phages will continue to reveal novel molecular mechanisms and will be important for the rational design of phage-based prophylaxis and therapies to prevent and treat bacterial infections, respectively. Here we delve into the molecular interactions of Vibrio species and phages.

Isolation and Characterization of a Newly Discovered Phage, V-YDF132, for Lysing Vibrio harveyi

A newly discovered lytic bacteriophage, V-YDF132, which efficiently infects the pathogenic strain of Vibrio harveyi, was isolated from aquaculture water collected in Yangjiang, China. Electron microscopy studies revealed that V-YDF132 belonged to the Siphoviridae family, with an icosahedral head and a long noncontractile tail. The phage has a latent period of 25 min and a burst size of 298 pfu/infected bacterium. V-YDF132 was stable from 37 to 50 °C. It has a wide range of stability (pH 5-11) and can resist adverse external environments. In addition, in vitro the phage V-YDF132 has a strong lytic effect on the host. Genome sequencing results revealed that V-YDF132 has a DNA genome of 84,375 bp with a GC content of 46.97%. In total, 115 putative open reading frames (ORFs) were predicted in the phage V-YDF132 genome. Meanwhile, the phage genome does not contain any known bacterial virulence genes or antimicrobial resistance genes. Comparison of the genomic features of the phage V-YDF132 and phylogenetic analysis revealed that V-YDF132 is a newly discovered Vibrio phage. Multiple genome comparisons and comparative genomics showed that V-YDF132 is in the same genus as Vibrio phages vB_VpS_PG28 (MT735630.2) and VH2_2019 (MN794238.1). Overall, the results indicate that V-YDF132 is potentially applicable for biological control of vibriosis.

Phage Revolution Against Multidrug-Resistant Clinical Pathogens in Southeast Asia

Southeast Asia (SEA) can be considered a hotspot of antimicrobial resistance (AMR) worldwide. As recent surveillance efforts in the region reported the emergence of multidrug-resistant (MDR) pathogens, the pursuit of therapeutic alternatives against AMR becomes a matter of utmost importance. Phage therapy, or the use of bacterial viruses called bacteriophages to kill bacterial pathogens, is among the standout therapeutic prospects. This narrative review highlights the current understanding of phages and strategies for a phage revolution in SEA. We define phage revolution as the radical use of phage therapy in infectious disease treatment against MDR infections, considering the scientific and regulatory standpoints of the region. We present a three-phase strategy to encourage a phage revolution in the SEA clinical setting, which involves: (1) enhancing phage discovery and characterization efforts, (2) creating and implementing laboratory protocols and clinical guidelines for the evaluation of phage activity, and (3) adapting regulatory standards for therapeutic phage formulations. We hope that this review will open avenues for scientific and policy-based discussions on phage therapy in SEA and eventually lead the way to its fullest potential in countering the threat of MDR pathogens in the region and worldwide.

Phage Therapy as a Focused Management Strategy in Aquaculture

Therapeutic bacteriophages, commonly called as phages, are a promising potential alternative to antibiotics in the management of bacterial infections of a wide range of organisms including cultured fish. Their natural immunogenicity often induces the modulation of a variated collection of immune responses within several types of immunocytes while promoting specific mechanisms of bacterial clearance. However, to achieve standardized treatments at the practical level and avoid possible side effects in cultivated fish, several improvements in the understanding of their biology and the associated genomes are required. Interestingly, a particular feature with therapeutic potential among all phages is the production of lytic enzymes. The use of such enzymes against human and livestock pathogens has already provided in vitro and in vivo promissory results. So far, the best-understood phages utilized to fight against either Gram-negative or Gram-positive bacterial species in fish culture are mainly restricted to the Myoviridae and Podoviridae, and the Siphoviridae, respectively. However, the current functional use of phages against bacterial pathogens of cultured fish is still in its infancy. Based on the available data, in this review, we summarize the current knowledge about phage, identify gaps, and provide insights into the possible bacterial control strategies they might represent for managing aquaculture-related bacterial diseases.

Biochemical characterization of LysVpKK5 endolysin from a marine vibriophage

Endolysins have been proposed as a potential antibacterial alternative for aquaculture, especially against Vibrio; the bacterial-agents that most frequently cause disease. Although multiple marine vibriophages have been characterized to date, research on vibriophage endolysins is recent. In this study, biochemical characterization of LysVpKK5 endolysin encoded by Vibrio parahaemolyticus-infecting VpKK5 phage was performed. In silico analysis revealed that LysVpKK5 possesses a conserved amidase_2 domain with a zinc-binding motif of high structural similarity to T7 lysozyme (RMSD = 0.107 Å). Contrary to expectations, the activity was inhibited with Zn²⁺ and was improved with other divalent cations, especially Ca²⁺. It showed optimal muralytic activity at pH 10, and curiously, no lytic activity at pH ≤ 7 was recorded. As for the thermal stability test, the optimal activity was recorded at 30 °C; the higher residual activity was recorded at 4 °C, and was lost at ≥ 50 °C. On the other hand, increasing NaCl concentrations reduced the activity gradually; the optimal activity was recorded at 50 mM NaCl. On the other hand, the enzymatic activity at 0.5 M NaCl was approx 30% and of approx 50% in seawater. LysVpKK5 endolysin exhibited a higher activity on V. parahaemolyticus ATCC-17802 strain, in comparison with AHPND + strains.

Isolation and Characterization of Six Vibrio parahaemolyticus Lytic Bacteriophages From Seafood Samples

Vibrio parahaemolyticus is a foodborne pathogen that is frequently isolated from a variety of seafood. To control this pathogenic Vibrio spp., the implementation of bacteriophages in aquaculture and food industries have shown a promising alternative to antibiotics. In this study, six bacteriophages isolated from the seafood samples demonstrated a narrow host range specificity that infecting only the V. parahaemolyticus strains. Morphological analysis revealed that bacteriophages Vp33, Vp22, Vp21, and Vp02 belong to the Podoviridae family, while bacteriophages Vp08 and Vp11 were categorized into the Siphoviridae family. All bacteriophages were composed of DNA genome and showed distinctive restriction fragment length polymorphism. The optimal MOI for bacteriophage propagation was determined to be 0.001 to 1. One-step growth curve revealed that the latent period ranged from 10 to 20 min, and the burst size of bacteriophage was approximately 17 to 51 PFU/cell. The influence of temperature and pH levels on the stability of bacteriophages showed that all bacteriophages were optimally stable over a wide range of temperatures and pH levels. In vitro lytic activity of all bacteriophages demonstrated to have a significant effect against V. parahaemolyticus. Besides, the application of a bacteriophage cocktail instead of a single bacteriophage suspension was observed to have a better efficiency to control the growth of V. parahaemolyticus. Results from this study provided a basic understanding of the physiological and biological properties of the isolated bacteriophages before it can be readily used as a biocontrol agent against the growth of V. parahaemolyticus.

Induction and Genome Analysis of HY01, a Newly Reported Prophage from an Emerging Shrimp Pathogen Vibrio campbellii

Vibrio campbellii is an emerging aquaculture pathogen that causes luminous vibriosis in farmed shrimp. Although prophages in various aquaculture pathogens have been widely reported, there is still limited knowledge regarding prophages in the genome of pathogenic V. campbellii. Here, we describe the full-genome sequence of a prophage named HY01, induced from the emerging shrimp pathogen V. campbellii HY01. The phage HY01 was induced by mitomycin C and was morphologically characterized as long tailed phage. V. campbellii phage HY01 is composed of 41,772 bp of dsDNA with a G+C content of 47.45%. A total of 60 open reading frames (ORFs) were identified, of which 31 could be predicted for their biological functions. Twenty seven out of 31 predicted protein coding regions were matched with several encoded proteins of various Enterobacteriaceae, Pseudomonadaceae, Vibrionaceae, and other phages of Gram-negative bacteria. Interestingly, the comparative genome analysis revealed that the phage HY01 was only distantly related to Vibrio phage Va_PF430-3_p42 of fish pathogen V. anguillarum but differed in genomic size and gene organization. The phylogenetic tree placed the phage together with Siphoviridae family. Additionally, a survey of Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR) spacers revealed two matching sequences between phage HY01 genome and viral spacer sequence of Vibrio spp. The spacer results combined with the synteny results suggest that the evolution of V. campbellii phage HY01 is driven by the horizontal genetic exchange between bacterial families belonging to the class of Gammaproteobacteria.

Characterization of vB_VpaP_MGD2, a newly isolated bacteriophage with biocontrol potential against multidrug-resistant Vibrio parahaemolyticus

Vibrio parahaemolyticus is a major foodborne pathogen and is also pathogenic to shrimp. Due to the emergence of multidrug-resistant V. parahaemolyticus strains, bacteriophages have shown promise as antimicrobial agents that could be used for controlling antibiotic-resistant strains. Here, a V. parahaemolyticus phage, vB_VpaP_MGD2, was isolated from a clam (Meretrix meretrix) and further characterized to evaluate its potential capability for biocontrol. Podophage vB_VpaP_MGD2 had a wide host range and was able to lyse 27 antibiotic-resistant V. parahaemolyticus strains. A one-step growth curve showed that vB_VpaP_MGD2 has a short latent period of 10 min and a large burst size of 244 phages per cell. Phage vB_VpaP_MGD2 was able to tolerate a wide range of temperature (30 °C-50 °C) and pH (pH 3-pH 10). Two multidrug-resistant strains (SH06 and SA411) were suppressed by treatment with phage vB_VpaP_MGD2 at a multiplicity of infection of 100 for 24 h without apparent regrowth of bacterial populations. The frequency of mutations causing bacteriophage resistance was relatively low (3.1 × 10^-6). Phage vB_VpaP_MGD2 has a double-stranded DNA with a genome size of 45,105 bp. Among the 48 open reading frames annotated in the genome, no lysogenic genes or virulence genes were detected. Sequence comparisons suggested that vB_VpaP_MGD2 is a member of a new species in the genus Zindervirus within the subfamily Autographivirinae. This is the first report of a member of the genus Zindervirus that can infect V. parahaemolyticus. These findings suggest that vB_VpaP_MGD2 may be a candidate biocontrol agent against early mortality syndrome/acute hepatopancreatic necrosis disease (EMS/AHPND) caused by multidrug-resistant V. parahaemolyticus in shrimp production.

Biological and Genomic Characterization of a Novel Jumbo Bacteriophage, vB_VhaM_pir03 with Broad Host Lytic Activity against Vibrio harveyi

Vibrio harveyi is a Gram-negative marine bacterium that causes major disease outbreaks and economic losses in aquaculture. Phage therapy has been considered as a potential alternative to antibiotics however, candidate bacteriophages require comprehensive characterization for a safe and practical phage therapy. In this work, a lytic novel jumbo bacteriophage, vB_VhaM_pir03 belonging to the Myoviridae family was isolated and characterized against V. harveyi type strain DSM19623. It had broad host lytic activity against 31 antibiotic-resistant strains of V. harveyi, V. alginolyticus, V. campbellii and V. owensii. Adsorption time of vB_VhaM_pir03 was determined at 6 min while the latent-phase was at 40 min and burst-size at 75 pfu/mL. vB_VhaM_pir03 was able to lyse several host strains at multiplicity-of-infections (MOI) 0.1 to 10. The genome of vB_VhaM_pir03 consists of 286,284 base pairs with 334 predicted open reading frames (ORFs). No virulence, antibiotic resistance, integrase encoding genes and transducing potential were detected. Phylogenetic and phylogenomic analysis showed that vB_VhaM_pir03 is a novel bacteriophage displaying the highest similarity to another jumbo phage, vB_BONAISHI infecting Vibrio coralliilyticus. Experimental phage therapy trial using brine shrimp, Artemia salina infected with V. harveyi demonstrated that vB_VhaM_pir03 was able to significantly reduce mortality 24 h post infection when administered at MOI 0.1 which suggests that it can be an excellent candidate for phage therapy.

Characterization and whole-genome sequencing of broad-host-range Salmonella-specific bacteriophages for bio-control

Salmonella Enteritidis (S. Enteritidis), which could cause human disease and death by consuming the contaminated food, is an important zoonotic pathogen. With the rapid increase of antibiotic resistance all over the world, bacteriophage-based bio-control has gradually attracted public attention widely. In order to find a suitable phage treating S. Enteritidis infection, four phages infecting S. Enteritidis were isolated from poultry fecal samples. Host range showed that four phages had a broad-host-range to Salmonella isolates. The morphological analysis illustrated that all of those phages were classified as the Myoviridae family. The one-step growth curve indicated that bacteriophage BPSELC-1 has a short latent period of about 10 min and a large burst size of 500 pfu/cell in comparison to the other three phages. Then phage BPSELC-1 was sequenced and conducted in vitro experiment. The genome of phage BPSELC-1 is 86,996 bp in size and has 140 putative genes containing structure proteins-encoding genes, tRNA genes and DNA replication or nucleotide metabolism genes. Importantly, no known virulence-associated, antibiotic and lysogeny-related genes were identified in the genome of BPSELC-1. In vitro experiment of phage treatment pointed out that the number of viable S. Enteritidis ATCC 13076 was reduced by 5.9×log₁₀ at MOI of 10² after 4 h. To the best of our knowledge, the phage BPSELC-1 exhibited higher efficiency in S. Enteritidis treatment compared to previous studies. Moreover, it is promising to be used as a broad-spectrum candidate against Salmonella infections in commercial owing to its broad-host-range.

Isolation and Characterization of the Novel Phages vB_VpS_BA3 and vB_VpS_CA8 for Lysing Vibrio parahaemolyticus

Accumulating evidence has indicated that the multiple drug resistant Vibrio parahaemolyticus may pose a serious threat to public health and economic concerns for humans globally. Here, two lytic bacteriophages, namely vB_VpS_BA3 and vB_VpS_CA8, were isolated from sewage collected in Guangzhou, China. Electron microscopy studies revealed both virions taxonomically belonged to the Siphoviridae family with icosahedral head and a long non-contractile tail. The double-stranded DNA genome of phage BA3 was composed of 58648 bp with a GC content of 46.30% while phage CA8 was 58480 bp with an average GC content of 46.42%. In total, 85 putative open reading frames (ORFs) were predicted in the phage BA3 genome while 84 were predicted in that of CA8. The ORFs were associated with phage structure, packing, host lysis, DNA metabolism, and additional functions. Furthermore, average nucleotide identity analysis, comparative genomic features and phylogenetic analysis revealed that BA3 and CA8 represented different isolates but novel members of the family, Siphoviridae. Regarding the host range of the 61 V. parahaemolyticus isolates, BA3 and CA8 had an infectivity of 8.2 and 36.1%, respectively. Furthermore, ∼100 plaque-forming units (pfu)/cell for phage BA3 and ∼180 pfu/cell for phage CA8 were determined to be the viral load under laboratory growth conditions. Accordingly, the phage-killing assay in vitro revealed that phage CA8 achieved approximately 3.65 log unit reductions. The present results indicate that CA8 is potentially applicable for biological control of multidrug resistant V. parahaemolyticus.

A novel vibriophage exhibits inhibitory activity against host protein synthesis machinery

Since the emergence of deadly pathogens and multidrug-resistant bacteria at an alarmingly increased rate, bacteriophages have been developed as a controlling bioagent to prevent the spread of pathogenic bacteria. One of these pathogens, disease-causing Vibrio parahaemolyticus (VPAHPND) which induces acute hepatopancreatic necrosis, is considered one of the deadliest shrimp pathogens, and has recently become resistant to various classes of antibiotics. Here, we discovered a novel vibriophage that specifically targets the vibrio host, VPAHPND. The vibriophage, designated Seahorse, was classified in the family Siphoviridae because of its icosahedral capsid surrounded by head fibers and a non-contractile long tail. Phage Seahorse was able to infect the host in a broad range of pH and temperatures, and it had a relatively short latent period (nearly 30 minutes) in which it produced progeny at 72 particles per cell at the end of its lytic cycle. Upon phage infection, the host nucleoid condensed and became toroidal, similar to the bacterial DNA morphology seen during tetracycline treatment, suggesting that phage Seahorse hijacked host biosynthesis pathways through protein translation. As phage Seahorse genome encodes 48 open reading frames with many hypothetical proteins, this genome could be a potential untapped resource for the discovery of phage-derived therapeutic proteins.

Genome characterization of novel lytic Myoviridae bacteriophage ϕVP-1 enhances its applicability against MDR-biofilm-forming Vibrio parahaemolyticus

A pathogen of significance in the aquaculture sector, the Gram-negative marine bacterium Vibrio parahaemolyticus causes gastroenteritis associated with consumption of improperly prepared seafood. This bacterium can be controlled using lytic bacteriophages as an alternative to antibiotics. ϕVP-1 is a lytic phage of V. parahaemolyticus that was isolated from an aquafarm water sample with the aim of assessing its potential as a bio-control agent and determining its physicochemical properties and genomic sequence. Morphological analysis by transmission electron microscopy and phylogenetic analysis based on the large terminase subunit gene showed that this phage belongs to the family Myoviridae. It could infect multiple-drug-resistant (MDR) V. parahaemolyticus and V. alginolyticus strains of mangrove and seafood origin. With a maximum adsorption time of 30 min, ϕVP-1 has a short latent period of 10 min with burst size of 44 particles/cell. Whole-genome sequencing was done using the Illumina platform, and annotation was done using GeneMarkS and Prodigal. The 150,764bp genome with an overall G+C content of 41.84% had 203 putative protein-encoding open reading frames, one tRNA gene, and 66 predicted promoters. A number of putative DNA replication and regulation, DNA packaging and structure, and host lysis genes were identified. Comparison of the ϕVP-1 genome sequence to those of known Vibrio phages indicated little discernible DNA sequence similarity, suggesting that ϕVP-1 is a novel Vibrio phage. Sequence analysis revealed the presence of 64 potential ORFs with a T4-like genomic organization. In silico analysis suggested an obligate lytic life cycle and showed the absence of lysogeny or virulence genes. The complete sequence of ϕVP-1 was annotated and deposited in the GenBank database (accession no. MH363700). The genetic features of this novel phage suggest that it might be applicable for phage therapy against pathogenic strains of V. parahaemolyticus.

A Novel Benthic Phage Infecting Shewanella with Strong Replication Ability

The coastal sediments were considered to contain diverse phages playing important roles in driving biogeochemical cycles based on genetic analysis. However, till now, benthic phages in coastal sediments were very rarely isolated, which largely limits our understanding of their biological characteristics. Here, we describe a novel lytic phage (named Shewanella phage S0112) isolated from the coastal sediments of the Yellow Sea infecting a sediment bacterium of the genus Shewanella. The phage has a very high replication capability, with the burst size of ca. 1170 phage particles per infected cell, which is 5–10 times higher than that of most phages isolated before. Meanwhile, the latent period of this phage is relatively longer, which might ensure adequate time for phage replication. The phage has a double-stranded DNA genome comprising 62,286 bp with 102 ORFs, ca. 60% of which are functionally unknown. The expression products of 16 ORF genes, mainly structural proteins, were identified by LC-MS/MS analysis. Besides the general DNA metabolism and structure assembly genes in the phage genome, there is a cluster of auxiliary metabolic genes that may be involved in 7-cyano-7-deazaguanine (preQ₀) biosynthesis. Meanwhile, a pyrophosphohydrolase (MazG) gene being considered as a regulator of programmed cell death or involving in host stringer responses is inserted in this gene cluster. Comparative genomic and phylogenetic analysis both revealed a great novelty of phage S0112. This study represents the first report of a benthic phage infecting Shewanella, which also sheds light on the phage–host interactions in coastal sediments.