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

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.

Characterization and genomic analysis of a broad-spectrum lytic phage PG288: A potential natural therapy candidate for Vibrio infections

Vibrio parahaemolyticus, an important zoonotic pathogen, can cause severe diseases and even death in aquatic animals and humans. As the widespread use of antibiotics gradually diminishes their effectiveness, phages, which can selectively lyse bacteria, are garnering increased attention as a valuable alternative antibacterial strategy. This study characterized PG288, a lytic phage utilizing V. parahaemolyticus strain G855 as its host. Morphologically, the phage features a polyhedral head and a long, non-retractable tail. Bactericidal assays revealed that phage PG288 exhibited a strong lytic ability against V. parahaemolyticus strain G855 and demonstrated a broad host range, as evidenced by the ability to infect several distinct Vibrio species. The one-step growth curve indicated a latent period of approximately 50 min for phage PG288, with a burst size of roughly 92 PFU per cell. Additionally, phage PG288 exhibited remarkable stability within a temperature range of 20-50°C and a pH range of 4-10. Genomic analysis unveiled 105 ORFs within phage PG288, notably devoid of genes associated with antibiotic resistance, virulence, and lysogenic activity. Phylogenetic analysis conclusively identified it as a new member of the genus Mardecavirus within the class Caudoviricetes. In summary, this study contributes valuable insights to the phage database, presenting phage PG288 as a promising candidate for phage therapies against Vibrio infections.

Positive and negative aspects of bacteriophages and their immense role in the food chain

Bacteriophages infect and replicate inside a bacterial host as well as serve as natural bio-control agents. Phages were once viewed as nuisances that caused fermentation failures with cheese-making and other industrial processes, which lead to economic losses, but phages are now increasingly being observed as being promising antimicrobials that can fight against spoilage and pathogenic bacteria. Pathogen-free meals that fulfil industry requirements without synthetic additives are always in demand in the food sector. This study introduces the readers to the history, sources, and biology of bacteriophages, which include their host ranges, absorption mechanisms, lytic profiles, lysogenic profiles, and the influence of external factors on the growth of phages. Phages and their derivatives have emerged as antimicrobial agents, biodetectors, and biofilm controllers, which have been comprehensively discussed in addition to their potential applications in the food and gastrointestinal tract, and they are a feasible and safe option for preventing, treating, and/or eradicating contaminants in various foods and food processing environments. Furthermore, phages and phage-derived lytic proteins can be considered potential antimicrobials in the traditional farm-to-fork context, which include phage-based mixtures and commercially available phage products. This paper concludes with some potential safety concerns that need to be addressed to enable bacteriophage use efficiently.

Sources and contamination routes of seafood with human pathogenic Vibrio spp.: A Farm-to-Fork approach

Vibrio spp., known human foodborne pathogens, thrive in freshwater, estuaries, and marine settings, causing vibriosis upon ingestion. The rising global vibriosis cases due to climate change necessitate a deeper understanding of Vibrio epidemiology and human transmission. This review delves into Vibrio contamination in seafood, scrutinizing its sources and pathways. We comprehensively assess the contamination of human-pathogenic Vibrio in the seafood chain, covering raw materials to processed products. A "Farm-to-Fork" approach, aligned with the One Health concept, is essential for grasping the complex nature of Vibrio contamination. Vibrio's widespread presence in natural and farmed aquatic environments establishes them as potential entry points into the seafood chain. Environmental factors, including climate, human activities, and wildlife, influence contamination sources and routes, underscoring the need to understand the origin and transmission of pathogens in raw seafood. Once within the seafood chain, the formation of protective biofilms on various surfaces in production and processing poses significant food safety risks, necessitating proper cleaning and disinfection to prevent microbial residue. In addition, inadequate seafood handling, from inappropriate processing procedures to cross-contamination via pests or seafood handlers, significantly contributes to Vibrio food contamination, thus warranting attention to reduce risks. Information presented here support the imperative for proactive measures, robust research, and interdisciplinary collaboration in order to effectively mitigate the risks posed by human pathogenic Vibrio contamination, safeguarding public health and global food security. This review serves as a crucial resource for researchers, industrials, and policymakers, equipping them with the knowledge to develop biosecurity measures associated with Vibrio-contaminated seafood.

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.

Safety Properties of Escherichia coli O157:H7 Specific Bacteriophages: Recent Advances for Food Safety

Shiga-toxin-producing Escherichia coli (STEC) is typically detected on food products mainly due to cross-contamination with faecal matter. The serotype O157:H7 has been of major public health concern due to the severity of illness caused, prevalence, and management. In the food chain, the main methods of controlling contamination by foodborne pathogens often involve the application of antimicrobial agents, which are now becoming less efficient. There is a growing need for the development of new approaches to combat these pathogens, especially those that harbour antimicrobial resistant and virulent determinants. Strategies to also limit their presence on food contact surfaces and food matrices are needed to prevent their transmission. Recent studies have revealed that bacteriophages are useful non-antibiotic options for biocontrol of E. coli O157:H7 in both animals and humans. Phage biocontrol can significantly reduce E. coli O157:H7, thereby improving food safety. However, before being certified as potential biocontrol agents, the safety of the phage candidates must be resolved to satisfy regulatory standards, particularly regarding phage resistance, antigenic properties, and toxigenic properties. In this review, we provide a general description of the main virulence elements of E. coli O157:H7 and present detailed reports that support the proposals that phages infecting E. coli O157:H7 are potential biocontrol agents. This paper also outlines the mechanism of E. coli O157:H7 resistance to phages and the safety concerns associated with the use of phages as a biocontrol.

Polymorphism and mutational diversity of virulence (vcgCPI/vcgCPE) and resistance determinants (aac(3)-IIa, (aacC2, strA, Sul 1, and 11) among human pathogenic Vibrio species recovered from surface waters in South-Western districts of Uganda

BACKGROUND

Vibrio species are among the autochthonous bacterial  populations found in surface waters and associated with various life-threatening extraintestinal diseases, especially in human populations with underlying illnesses and wound infections. Presently, very diminutive information exists regarding these species' mutational diversity of virulence and resistance genes. This study evaluated variations in endonucleases and mutational diversity of the virulence and resistance genes of Vibrio isolates, harboring virulence-correlated gene (vcgCPI), dihydropteroate synthase type 1 and type II genes (Sul 1 and 11), (aadA) aminoglycoside (3'') (9) adenylyltransferase gene, (aac(3)-IIa, (aacC2)a, aminoglycoside N(3)-acetyltransferase III, and (strA) aminoglycoside 3'-phosphotransferase resistance genes.

METHODS

Using combinations of molecular biology techniques, bioinformatics tools, and sequence analysis.

RESULTS

Our result revealed various nucleotide variations in virulence determinants of V. vulnificus (vcgCPI) at nucleotide positions (codon) 73-75 (A → G) and 300-302 (N → S). The aminoglycosides resistance gene (aadA) of Vibrio species depicts a nucleotide difference at position 482 (A → G), while the aminoglycosides resistance gene (sul 1 and 11) showed two variable regions of nucleotide polymorphism (102 and 140). The amino acid differences exist with the nucleotide polymorphism at position 140 (A → E). The banding patterns produced by the restriction enzymes HinP1I, MwoI, and StyD4I showed significant variations. Also, the restriction enzyme digestion of protein dihydropteroate synthase type 1 and type II genes (Sul 1 and 11) differed significantly, while enzymes DpnI and Hinf1 indicate no significant differences. The restriction enzyme NlaIV showed no band compared to reference isolates from the GenBank. However, the resistant determinants show significant point nucleotide mutation, which does not produce any amino acid change with diverse polymorphic regions, as revealed in the restriction digest profile.

CONCLUSION

The described virulence and resistance determinants possess specific polymorphic locus relevant to pathogenomics studies, pharmacogenomic, and control of such water-associated strains.

Vibrio-infecting bacteriophages and their potential to control biofilm

The emergence and spread of antibiotic-resistant pathogenic bacteria have necessitated finding new control alternatives. Under these circumstances, lytic bacteriophages offer a viable and promising option. This review focuses on Vibrio-infecting bacteriophages and the characteristics that make them suitable for application in the food and aquaculture industries. Bacteria, particularly Vibrio spp., can produce biofilms under stress conditions. Therefore, this review summarizes several anti-biofilm mechanisms that phages have, such as stimulating the host bacteria to produce biofilm-degrading enzymes, utilizing tail depolymerases, and penetrating matured biofilms through water channels. Additionally, the advantages of bacteriophages over antibiotics, such as a lower probability of developing resistance and the ability to infect dormant cells, are discussed. Finally, this review presents future research prospects related to further utilization of phages in diverse fields.

Characterization of vB_ValM_PVA8, a broad-host-range bacteriophage infecting Vibrio alginolyticus and Vibrio parahaemolyticus

Phage therapy was taken as an alternative strategy to antibiotics in shrimp farming for the control of Vibrio species of Vibrio parahaemolyticus and Vibrio alginolyticus, which cause substantial mortality and significant economic losses. In this study, a new Vibrio phage vB_ValM_PVA8 (PVA8), which could efficiently infect pathogenic isolates of V. alginolyticus and V. parahaemolyticus, was isolated from sewage water and characterized by microbiological and in silico genomic analyses. The phage was characterized to be a member of the Straboviridae family with elongated head and contractile tail by transmission electron microscopy. Genome sequencing showed that PVA8 had a 246,348-bp double-stranded DNA genome with a G + C content of 42.6%. It harbored totally 388 putative open reading frames (ORFs), among them 92 (23.71%) assigned to functional genes. Up to 27 transfer RNA (tRNA) genes were found in the genome, and the genes for virulence, antibiotic resistance, and lysogeny were not detected. NCBI genomic blasting results and the phylogenetic analysis based on the sequences of the large terminase subunits and the DNA polymerase indicated that PVA8 shared considerable similarity with Vibrio phage V09 and bacteriophage KVP40. The phage had a latent period of 20 min and a burst size of 309 PFUs/infected cell with the host V. alginolyticus, and it was stable over a broad pH range (4.0-11.0) and a wide temperature span (-80°C to 60°C), respectively, which may benefit its feasibility for phage therapy. In addition, it had the minimum multiplicity of infection (MOI) of 0.0000001, which revealed its strong multiplication capacity. The shrimp cultivation lab trials demonstrated that PVA8 could be applied in treating pathogenic V. parahaemolyticus infection disease of shrimp with a survival rate of 88.89% comparing to that of 34.43% in the infected group, and the pond application trails confirmed that the implementation of PVA8 could rapidly yet effectively reduce the level of the Vibrio. Taken together, PVA8 may be potential to be explored as a promising biological agent for Vibrio control in aquaculture farming industry.

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.

Interactions of Vibrio phages and their hosts in aquatic environments

Bacteriophages (phages) are viruses that specifically infect bacteria. These viruses were discovered a century ago and have been used as a model system in microbial genetics and molecular biology. In order to survive, bacteria have to quickly adapt to phage challenges in their natural settings. In turn, phages continuously develop/evolve mechanisms for battling host defenses. A deeper understanding of the arms race between bacteria and phages is essential for the rational design of phage-based prophylaxis and therapies to prevent and treat bacterial infections. Vibrio species and their phages (vibriophages) are a suitable model to study these interactions. Phages are highly ubiquitous in aquatic environments and Vibrio are waterborne bacteria that must survive the constant attack by phages for successful transmission to their hosts. Here, we review relevant literature from the past two years to delve into the molecular interactions of Vibrio species and their phages in aquatic niches.

Characterization of Virulent T4-Like Acinetobacter baumannii Bacteriophages DLP1 and DLP2

The world is currently facing a global health crisis due to the rapid increase in antimicrobial-resistant bacterial infections. One of the most concerning pathogens is Acinetobacter baumannii, which is listed as a Priority 1 pathogen by the World Health Organization. This Gram-negative bacterium has many intrinsic antibiotic resistance mechanisms and the ability to quickly acquire new resistance determinants from its environment. A limited number of effective antibiotics against this pathogen complicates the treatment of A. baumannii infections. A potential treatment option that is rapidly gaining interest is “phage therapy”, or the clinical application of bacteriophages to selectively kill bacteria. The myoviruses DLP1 and DLP2 (vB_AbaM-DLP_1 and vB_AbaM-DLP_2, respectively) were isolated from sewage samples using a capsule minus variant of A. baumannii strain AB5075. Host range analysis of these phages against 107 A. baumannii strains shows a limited host range, infecting 15 and 21 for phages DLP1 and DLP2, respectively. Phage DLP1 has a large burst size of 239 PFU/cell, a latency period of 20 min, and virulence index of 0.93. In contrast, DLP2 has a smaller burst size of 24 PFU/cell, a latency period of 20 min, and virulence index of 0.86. Both phages show potential for use as therapeutics to combat A. baumannii infections.

Phenotypic characterization of phage vB_vcM_Kuja

Bacteriophage therapy targeting the increasingly resistant Vibrio cholerae is highly needed. Hence, studying the phenotypic behavior of potential phages under different conditions is a prerequisite to delivering the phage in an active infective form. The objective of this study was to characterize phage VP4 (vB_vcM_Kuja), an environmental vibriophage isolated from River Kuja in Migori County, Kenya in 2015. The phenotypic characteristics of the phage were determined using a one-step growth curve, restriction digestion profile, pH, and temperature stability tests. The results revealed that the phage is stable through a wide range of temperatures (20-50°C) and maintains its plaque-forming ability at pH ranging from 6 to 12. The one-step growth curve showed a latent period falling between 40 and 60 min, while burst size ranged from 23 to 30 plaque-forming units/10 µl at the same host strain. The restriction digestion pattern using EcoRI, SalI, HindIII, and XhoI enzymes showed that HindIII could cut the phage genome. The phage DNA could not be restricted by the other three enzymes. The findings of this study can be used in future studies to determine phage-host interactions.

Characterization and genome analysis of six novel Vibrio parahaemolyticus phages associated with acute hepatopancreatic necrosis disease (AHPND)

Vibrio parahaemolyticus causes acute hepatopancreatic necrosis disease (AHPND) in farmed shrimp. Due to its damage potential, which could be as high as a 100% mortality rate, bacteriophages have emerged as a promising natural control intervention other than antibiotics, yet multiple roadblocks need to be overcome. In this study, six bacteriophages isolated from seafood samples, seawater, and estuary water in Sinaloa, Mexico, demonstrated a narrow host range among Mexican AHPND-causing V. parahaemolyticus. All bacteriophages are composed of a double-stranded DNA genome with lengths ranging between 43,268 and 57,805 bp. All six phages exhibited latency periods of 10-30 min and burst sizes of 34-168 viral particles per infected cell. The optimal MOI for bacteriophage propagation was 0.01-1. No transfer RNA (tRNA), virulence, or resistance genes were found in either genome, and the life cycle of these phages was classified as virulent by the PhageAI platform. Phylogenetic and comparative genomics analyzes assigned phages M3, C2, M9, and M83 as new species not yet reported within the genus Maculvirus, Autographiviridae family. ALK and CHI phages were assigned as new members of a new genus not yet classified within the subfamily Queuovirinae. The findings highlight the potential of CHI, ALK, M3, C2, M9, and M83 as promising alternatives against AHPND-causing V. parahaemolyticus from Mexico.

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.

Coastal water bacteriophages infect various sets of Vibrio parahaemolyticus sequence types

Introduction

Gastrointestinal illnesses associated with the consumption of shellfish contaminated with Vibrio parahaemolyticus have a negative impact on the shellfish industry due to recalls and loss of consumer confidence in products. This bacterial pathogen is very diverse and specific sequence types (STs), ST631 and ST36, have emerged as prevalent causes of Vibrio foodborne disease outbreaks in the US, though other STs have been implicated in sporadic cases. We investigated whether bacteriophages could be used as a proxy to monitor for the presence of distinct V. parahaemolyticus STs in coastal waters.

Methods

For this purpose, bacteriophages infecting V. parahaemolyticus were isolated from water samples collected on the Northeast Atlantic coast. The isolated phages were tested against a collection of 29 V. parahaemolyticus isolates representing 18 STs, including six clonal complexes (CC). Four distinct phages were identified based on their ability to infect different sets of V. parahaemolyticus isolates.

Results and Discussion

Overall, the 29 bacterial isolates segregated into one of eight patterns of susceptibility, ranging from resistance to all four phages to susceptibility to any number of phages. STs represented by more than one bacterial isolate segregated within the same pattern of susceptibility except for one V. parahaemolyticus ST. Other patterns of susceptibility included exclusively clinical isolates represented by distinct STs. Overall, this study suggests that phages populating coastal waters could be exploited to monitor for the presence of V. parahaemolyticus STs known to cause foodborne outbreaks.

Vibriosis Outbreaks in Aquaculture: Addressing Environmental and Public Health Concerns and Preventive Therapies Using Gilthead Seabream Farming as a Model System

Bacterial and viral diseases in aquaculture result in severe production and economic losses. Among pathogenic bacteria, species belonging to the Vibrio genus are one of the most common and widespread disease-causing agents. Vibrio infections play a leading role in constraining the sustainable growth of the aquaculture sector worldwide and, consequently, are the target of manifold disease prevention strategies. During the early, larval stages of development, Vibrio species are a common cause of high mortality rates in reared fish and shellfish, circumstances under which the host organisms might be highly susceptible to disease preventive or treatment strategies such as vaccines and antibiotics use, respectively. Regardless of host developmental stage, Vibrio infections may occur suddenly and can lead to the loss of the entire population reared in a given aquaculture system. Furthermore, the frequency of Vibrio-associated diseases in humans is increasing globally and has been linked to anthropic activities, in particular human-driven climate change and intensive livestock production. In this context, here we cover the current knowledge of Vibrio infections in fish aquaculture, with a focus on the model species gilthead seabream (Sparus aurata), a highly valuable reared fish in the Mediterranean climatic zone. Molecular methods currently used for fast detection and identification of Vibrio pathogens and their antibiotic resistance profiles are addressed. Targeted therapeutic approaches are critically examined. They include vaccination, phage therapy and probiotics supplementation, which bear promise in supressing vibriosis in land-based fish rearing and in mitigating possible threats to human health and the environment. This literature review suggests that antibiotic resistance is increasing among Vibrio species, with the use of probiotics constituting a promising, sustainable approach to prevent Vibrio infections in aquaculture.

Bacteriostatic effects of phage F23s1 and its endolysin on Vibrio parahaemolyticus

Vibrio parahaemolyticus is a common foodborne pathogenic bacterium and drug-resistant strains are now widespread. Phages led by drug-resistant V. parahaemolyticus strains are promising means to decrease the pressure on public health. We isolated a V. parahaemolyticus-specific bacteriophage F23s1 that was active at wide ranges of temperature (30-60°C) and pH (4-10). Phage F23s1 exhibited a specific host range; in that, only 13 of the 23 V. parahaemolyticus strains were lysed. F23s1 effectively inhibited the growth of V. parahaemolyticus strain F23 in shrimp at 25°C within 12 h at a multiplicity of infection of 1000. We sequenced the genome of phage F23s1 which comprised a 76,648-bp DNA with 105 open reading frames (ORFs) and identified an endolysin gene ORF52 that was then cloned and successfully expressed in Escherichia coli. The recombinant ORF52 protein significantly decreased OD_600 nm of V. parahaemolyticus F23 from 0.978 to 0.249 when used at 20 µmol/L within 60 min. The endolysin also showed lytic activity against a panel of 23 drug-resistant V. parahaemolyticus and 12 Salmonella strains with a higher lytic ability for V. parahaemolyticus. The phage F23s1 and its endolysin will be useful for preventing and controlling V. parahaemolyticus in food safety.

An Anti-MRSA Phage From Raw Fish Rinse: Stability Evaluation and Production Optimization

Accumulating evidence has denoted the danger of resistance in tenacious organisms like methicillin-resistant Staphylococcus aureus (MRSA). MRSA, a supple bacterium that adopts a variety of antibiotic resistance mechanisms, is the cause of multiple life-threatening conditions. Approaching a post-antibiotic era, bacteria-specific natural predators, bacteriophages, are now given the chance to prove eligible for joining the antibacterial weaponry. Considering the foregoing, this study aimed at isolating bacteriophages with promising anti-MRSA lytic activity, followed by characterization and optimization of the production of the bacteriophage with the broadest host range. Five phages were isolated from different environmental sources including the rinse of raw chicken egg, raw milk, and, remarkably, the raw meat rinses of chicken and fish. Examined for lytic activity against a set of 23 MRSA isolates collected from various clinical specimens, all five phages showed relatively broad host ranges with the bacteriophage originally isolated from raw fish rinse showing lytic activity against all the isolates tested. This phage is suggested to be a member of Siphoviridae family, order Caudovirales, as revealed by electron microscopy. It also exhibited good thermal stability and viability at different pH grades. Moreover, it showed reasonable stability against UV light and all viricidal organic solvents tested. Optimization using D-optimal design by response surface methodology was carried out to enhance the phage yield. The optimum conditions suggested by the generated model were a pH value of 7, a carbon source of 0.5% w/v sucrose, and a nitrogen source of 0.1% w/v peptone, at a temperature of 28°C and a bacterial inoculum size of 107 CFU/ml, resulting in a 2 log-fold increase in the produced bacteriophage titer. Overall, the above findings indicate the lytic ability inflicted by this virus on MRSA. Apparently, its stability under some of the extreme conditions tested implies its potential to be a candidate for pharmaceutical formulation as an anti-MRSA therapeutic tool. We hope that bacteriophages could tip the balance in favor of the human front in their battle against multidrug-resistant pathogens.

Bacteriophage therapy in aquaculture: current status and future challenges

The escalation of antibiotic resistance has revitalized bacteriophage (phage) therapy. Recently, phage therapy has been gradually applied in medicine, agriculture, food, and environmental fields due to its distinctive features of high efficiency, specificity, and environmental friendliness compared to antibiotics. Likewise, phage therapy also holds great promise in controlling pathogenic bacteria in aquaculture. The application of phage therapy instead of antibiotics to eliminate pathogenic bacteria such as Vibrio, Pseudomonas, Aeromonas, and Flavobacterium and to reduce fish mortality in aquaculture has been frequently reported. In this context, the present review summarizes and analyzes the current status of phage therapy in aquaculture, focusing on the key parameters of phage application, such as phage isolation, selection, dosage, and administration modes, and introducing the strategies and methods to boost efficacy and restrain the emergence of resistance. In addition, we discussed the human safety, environmental friendliness, and techno-economic practicability of phage therapy in aquaculture. Finally, this review outlines the current challenges of phage therapy application in aquaculture from the perspectives of phage resistance, phage-mediated resistance gene transfer, and effects on the host immune system.

Comparative genome analyses of five Vibrio penaeicida strains provide insights into their virulence-related factors

Vibrio penaeicida (family Vibrionaceae) is an important bacterial pathogen that affects Japanese shrimp aquaculture. Only two whole-genome sequences of V. penaeicida are publicly available, which has hampered our understanding of the pathogenesis of shrimp vibriosis caused by this bacterium. To gain insight into the genetic features, evolution and pathogenicity of V. penaeicida, we sequenced five V. penaeicida strains (IFO 15640^T, IFO 15641, IFO 15642, TUMSAT-OK1 and TUMSAT-OK2) and performed comparative genomic analyses. Virulence factors and mobile genetic elements were detected. Furthermore, average nucleotide identities (ANIs), clusters of orthologous groups and phylogenetic relationships were evaluated. The V. penaeicida genome consists of two circular chromosomes. Chromosome I sizes ranged from 4.1 to 4.3 Mb, the GC content ranged from 43.9 to 44.1 %, and the number of predicted protein-coding sequences (CDSs) ranged from 3620 to 3782. Chromosome II sizes ranged from 2.2 to 2.4 Mb, the GC content ranged from 43.5 to 43.8 %, and the number of predicted CDSs ranged from 1992 to 2273. All strains except IFO 15641 harboured one plasmid, having sizes that ranged from 150 to 285 kb. All five genomes had typical virulence factors, including adherence, anti-phagocytosis, flagella-related proteins and toxins (repeats-in-toxin and thermolabile haemolysin). The genomes also contained factors responsible for iron uptake and the type II, IV and VI secretion systems. The genome of strain TUMSAT-OK2 tended to encode more prophage regions than the other strains, whereas the genome of strain IFO 15640^T had the highest number of regions encoding genomic islands. For comparative genome analysis, we used V. penaeicida (strain CAIM 285^T) as a reference strain. ANIs between strain CAIM 285^T and the five V. penaeicida strains were >95 %, which indicated that these strains belong to the same species. Orthology cluster analysis showed that strains TUMSAT-OK1 and TUMSAT-OK2 had the greatest number of shared gene clusters, followed by strains CAIM 285^T and IFO 15640^T. These strains were also the most closely related to each other in a phylogenetic analysis. This study presents the first comparative genome analysis of V. penaeicida and these results will be useful for understanding the pathogenesis of this bacterium.

Prophage-encoded gene VpaChn25_0734 amplifies ecological persistence of Vibrio parahaemolyticus CHN25

Vibrio parahaemolyticus is a waterborne pathogen that can cause acute gastroenteritis, wound infection, and septicemia in humans. The molecular basis of its pathogenicity is not yet fully understood. Phages are found most abundantly in aquatic environments and play a critical role in horizontal gene transfer. Nevertheless, current literature on biological roles of prophage-encoded genes remaining in V. parahaemolyticus is rare. In this study, we characterized one such gene VpaChn25_0734 (543-bp) in V. parahaemolyticus CHN25 genome. A deletion mutant ΔVpaChn25_0734 (543-bp) was obtained by homologous recombination, and a revertant ΔVpaChn25_0734-com (543-bp) was also constructed. The ΔVpaChn25_0734 (543-bp) mutant was defective in growth and swimming mobility particularly at lower temperatures and/or pH 7.0–8.5. Cell surface hydrophobicity and biofilm formation were significantly decreased in the ΔVpaChn25_0734 (543-bp) mutant (p < 0.05). Based on the in vitro Caco-2 cell model, the deletion of VpaChn25_0734 (543-bp) gene significantly reduced the cytotoxicity of V. parahaemolyticus CHN25 to human intestinal epithelial cells (p < 0.05). Comparative secretomic and transcriptomic analyses revealed a slightly increased extracellular proteins, and thirteen significantly changed metabolic pathways in the ΔVpaChn25_0734 (543-bp) mutant, showing down-regulated carbon source transport and utilization, biofilm formation, and type II secretion system (p < 0.05), consistent with the observed defective phenotypes. Taken, the prophage-encoded gene VpaChn25_0734 (543-bp) enhanced V. parahaemolyticus CHN25 fitness for survival in the environment and the host. The results in this study facilitate better understanding of pathogenesis and genome evolution of V. parahaemolyticus, the leading sea foodborne pathogen worldwide.

Rapid detection of Vibrio parahaemolyticus using magnetic nanobead-based immunoseparation and quantum dot-based immunofluorescence

In recent years, the scale of population exposure and food poisoning caused by Vibrio parahaemolyticus (V. parahaemolyticus) has shown a significant upward trend, becoming one of the primary food-borne pathogens. Herein, we developed a rapid and sensitive detection of V. parahaemolyticus by integrating the technology of magnetic nanobeads (MBs) based immunoseparation (IMS) with quantum dots (QDs) based immunofluorescence. Firstly, specific rabbit polyclone IgG antibodies (IgG) and chicken egg yolk antibodies (IgY) of V. parahaemolyticus were prepared. Then two sizes of MBs (1 μm; 180 nm) were coupled with IgG to form immuno-MB (IMB) capture probes for evaluating the effect of different sizes on the detection efficiency. For QDs, they were conjugated with IgY to form fluorescent reporting probes. In the process of detection, IMB probes were used to separate V. parahaemolyticus and then these complexes were labeled by QD probes on the principle of double antibody sandwich. The fluorescence intensity of the IMB-V. parahaemolyticus-QD complexes was measured by a fluorescence spectrophotometer. The detection method takes 150 min with a detection limit of 102 cfu mL-1 ranging from 102 to 106 cfu mL-1 and it has been shown to work satisfactorily in real food samples.