Vibrio parahaemolyticus and its specific bacteriophages as an indicator in cockles (Anadara granosa) for the risk of V. parahaemolyticus infection in Southern Thailand

Isolation, characterization and genomic analysis of bacteriophages for biocontrol of vibriosis caused by Vibrio alginolyticus

Vibrio alginolyticus is a significant opportunistic pathogen in marine environments, affecting both marine organisms and humans. The rise of antibiotic-resistant strains has prompted the exploration of bacteriophages as alternative biological control agents. In this study, 414 lytic bacteriophages specific to V. alginolyticus were isolated from various seafood and environmental samples. Phages P122, P125, and P160 demonstrated the broadest host range, effectively lysing 79.01 % of fish pathogenic V. alginolyticus strains and 44.69 % of environmental strains. However, no activity was observed against clinical V. alginolyticus strains or other tested species, including V. harveyi, Escherichia coli, Staphylococcus aureus, and Aeromonas hydrophila. One-step growth curve analysis revealed latent periods of 40 to 60 min and burst sizes ranging from 140 to 367 PFU/infected cells. Transmission electron microscopy (TEM) classified these phages within the class of Caudoviricetes with an icosahedral head and a long non-contractile tail. Moreover, whole-genome sequencing (WGS) identified genome sizes of approximately 76 kb, with 272-280 open reading frames (ORFs), no tRNA and pathogenic-associated genes. Comparative genomic analysis showed over 97 % similarity with other Vibrio phages. Phylogenetic analysis based on the terminase subunit also confirmed phages P122, P125, and P160 belonging to the class of Caudoviricetes. The phages were non-toxic to Galleria mellonella larvae and showed promise in reducing mortality rates when used as a cocktail treatment. The study highlights the potential of these phages as effective biocontrol agents in aquaculture, offering a promising alternative to antibiotics for managing Vibrio infections.

Genome-wide expanding of genetic evolution and potential pathogenicity in Vibrio alginolyticus

Vibrio alginolyticus, an emergent species of Vibrio genus, exists in aquatic and marine environments. It has undergone genetic diversification, but its detailed genomic diversity is still unclear. Here, we performed a multi-dimensional comparative genomic analysis to explore the population phylogeny, virulence-related genes and potential drug resistance genes of 184 V. alginolyticus isolates. Although genetic diversity is complex, we analysed the population structure using three sub-datasets, including the subdivision for three lineages into sublineages and the distribution of strains in the marine ecological niche. Accessory genes, most of which reclassified V. alginolyticus genomes as different but with relatively close affinities, were nonuniformly distributed among these isolates. We demonstrated that the spread of some post-evolutionary isolates (mainly L3 strains isolated from Chinese territorial seas) was likely to be closely related to human activities, whereas other more ancestral strains (strains in the L1 and L2) tended to be locally endemic and formed clonal complex groups. In terms of pathogenicity, the potential virulence factors were mainly associated with toxin, adherence, motility, chemotaxis, and the type III secretion system (T3SS). We also found five types of antibacterial drug resistance genes. The prevalence of β-lactam resistance genes was 100%, which indicated that there may be a potential risk of natural resistance to β-lactam drugs. Our study reveals insights into genomic characteristics, evolution and potential virulence-associated gene profiles of V. alginolyticus.

Characterization and Genome Analysis of Vibrio campbellii Lytic Bacteriophage OPA17

Vibrio campbellii is a marine bacterium that is associated with luminous vibriosis, especially in the hatchery and nursery stages of penaeid shrimp cultivation worldwide, which has led to low survival rates of shrimp during aquaculture. Phage therapy has been reported as an alternative biocontrol agent which can reduce or replace the use of antibiotics and other chemicals. This study characterized a lytic V. campbellii bacteriophage, OPA17, originally isolated from bloody clams and investigated its biocontrol efficacy against V. campbellii infection in a model system, Artemia franciscana. Phage OPA17 lysed 83.89% of V. campbellii strains tested (n = 118) with clear plaque morphology. Some strains of Vibrio parahaemolyticus and Vibrio vulnificus were also infected by phage OPA17. Transmission electron microscopy and genetic features indicated that OPA17 belongs to the Siphoviridae family. The latent period and burst size of OPA17 were approximately 50 min and 123 PFU/cell, respectively. Moreover, it survived in artificial seawater throughout the 2-month study period and effectively destroyed Vibrio campbellii biofilms after 4 h of incubation. The addition of OPA17 significantly increased the survival of A. franciscana nauplii infected with V. campbellii. The genome sequence of OPA17 showed that it does not carry genes unsuitable for phage therapy. The phylogenetic tree analysis showed that OPA17 was closely related to the V. vulnificus lytic phage SSP002 (98.90% similarity), which was previously reported as a potential biocontrol agent. Accordingly, the results of this study provide valuable information regarding the potential biocontrol application of phage OPA17 against V. campbellii. IMPORTANCE V. campbellii is an emerging luminous pathogen associated with vibriosis, especially in marine shrimp hatcheries. Several strategies, including pond management and use of natural antimicrobials and probiotics, have been studied for control of this organism. Phage therapy is considered one of the effective biocontrol strategies against bacterial infections in aquaculture. However, there has been limited study of V. campbellii bacteriophages. In this study, V. campbellii-specific bacteriophage OPA17 was isolated, characterized, and investigated for its biocontrol efficacy against V. campbellii infection in an Artemia nauplii model. Phage OPA17 belongs to the Siphoviridae family and shares significant genome similarity to phage SSP002, a potential biocontrol agent against V. vulnificus infection in a murine model. However, the host range of OPA17 was broader than that of SSP002. Overall, we discuss the potential of OPA17 for phage therapy application in shrimp hatcheries.

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.

Development of an Electrochemical DNA Biosensor to Detect a Foodborne Pathogen

Vibrio parahaemolyticus (V. parahaemolyticus) is a common foodborne pathogen that contributes to a large proportion of public health problems globally, significantly affecting the rate of human mortality and morbidity. Conventional methods for the detection of V. parahaemolyticus such as culture-based methods, immunological assays, and molecular-based methods require complicated sample handling and are time-consuming, tedious, and costly. Recently, biosensors have proven to be a promising and comprehensive detection method with the advantages of fast detection, cost-effectiveness, and practicality. This research focuses on developing a rapid method of detecting V. parahaemolyticus with high selectivity and sensitivity using the principles of DNA hybridization. In the work, characterization of synthesized polylactic acid-stabilized gold nanoparticles (PLA-AuNPs) was achieved using X-ray Diffraction (XRD), Ultraviolet-visible Spectroscopy (UV-Vis), Transmission Electron Microscopy (TEM), Field-emission Scanning Electron Microscopy (FESEM), and Cyclic Voltammetry (CV). We also carried out further testing of stability, sensitivity, and reproducibility of the PLA-AuNPs. We found that the PLA-AuNPs formed a sound structure of stabilized nanoparticles in aqueous solution. We also observed that the sensitivity improved as a result of the smaller charge transfer resistance (Rct) value and an increase of active surface area (0.41 cm²). The development of our DNA biosensor was based on modification of a screen-printed carbon electrode (SPCE) with PLA-AuNPs and using methylene blue (MB) as the redox indicator. We assessed the immobilization and hybridization events by differential pulse voltammetry (DPV). We found that complementary, non-complementary, and mismatched oligonucleotides were specifically distinguished by the fabricated biosensor. It also showed reliably sensitive detection in cross-reactivity studies against various food-borne pathogens and in the identification of V. parahaemolyticus in fresh cockles.

Temperature Effect Study on Growth and Survival of PathogenicVibrio parahaemolyticusin Jinjiang Oyster(Crassostrea rivularis)with Rapid Count Method

The growth ofVibrio parahaemolyticus (V. parahaemolyticus)in oysters during postharvest storage increases the possibility of its infection in humans. In this work, to investigate the growth or survival profiles in different media, pathogenicV. parahaemolyticusin APW, Jinjiang oyster (JO,Crassostrea rivularis) slurry, and live JO were studied under different temperatures. All the strain populations were counted through our double-layer agar plate (DLAP) method. In APW, the pathogenicV. parahaemolyticusshowed continuous growth under 15, 25, and 35°C, while a decline in behavior was displayed under 5°C. The similar survival trend of pathogenicV. parahaemolyticusin JO slurry and live JO was observed under 5, 25, and 35°C, except the delayed growth or decline profile compared to APW. Under 15°C, they displayed decline and growth profile in JO slurry and live JO, respectively. These results indicate the different sensitivity of pathogenicV. parahaemolyticusin these matrices to temperature variation. Furthermore, nonpathogenicV. parahaemolyticusdisplayed little difference in survival profiles when inoculated in live JO under corresponding temperatures. The results indicate that inhibition or promotion effect could be regulated under different storage temperature for both pathogenic and nonpathogenic strains. Besides, the DLAP method showed the obvious quickness and efficiency during the bacteria count.