Isolation of a lytic bacteriophage against virulentAeromonas hydrophilafrom an organized equine farm

Evaluation of immunogenicity and protective efficacy of bacteriophage conjugated haemagglutinin based subunit vaccine against equine influenza virus in a murine model

Equine influenza (EI) is a highly contagious acute respiratory disease of equines caused by the H3N8 subtype of Influenza A virus i.e. equine influenza virus (EIV). Vaccination is an important and effective tool for the control of EI in equines. Most of the commercial influenza vaccines are produced in embryonated hen's eggs which has several inherent disadvantages. Hence, subunit vaccine based on recombinant haemagglutinin (HA) antigen, being the most important envelope glycoprotein has been extensively exploited for generating protective immune responses, against influenza A and B viruses. We hypothesized that novel vaccine formulation using baculovirus expressed recombinant HA1 (rHA1) protein coupled with bacteriophage will generate strong protective immune response against EIV. In the present study, the recombinant HA1 protein was produced in insect cells using recombinant baculovirus having cloned HA gene of EIV (Florida clade 2 sublineage) and the purified rHA1 was chemically coupled with bacteriophage using a crosslinker to produce rHA1-phage vaccine candidate. The protective efficacy of vaccine preparations of rHA1-phage conjugate and only rHA1 proteins were evaluated in mouse model through assessing serology, cytokine profiling, clinical signs, gross and histopathological changes, immunohistochemistry, and virus quantification. Immunization of vaccine preparations have stimulated moderate antibody response (ELISA titres-5760 ± 640 and 11,520 ± 1280 for rHA1 and rHA1-phage, respectively at 42 dpi) and elicited strong interferon (IFN)-γ expression levels after three immunizations of vaccine candidates. The immunized BALB/c mice were protected against challenge with wild EIV and resulted in reduced clinical signs and body weight loss, reduced pathological changes, decreased EIV antigen distribution, and restricted EIV replication in lungs and nasopharynx. In conclusion, the immune responses with moderate antibody titer and significantly higher cytokine responses generated by the rHA1-phage vaccine preparation without any adjuvant could be a novel vaccine candidate for quick vaccine preparation through further trials of vaccine in the natural host.

Characterization and application of a lytic jumbo phage ZPAH34 against multidrug-resistant Aeromonas hydrophila

Aeromonas hydrophila is an emerging foodborne pathogen causing human gastroenteritis. Aeromonas species isolated from food such as seafood presented multidrug-resistance (MDR), raising serious concerns regarding food safety and public health. The use of phages to infect bacteria is a defense against drug-resistant pathogens. In this study, phage ZPAH34 isolated from the lake sample exerted lytic activity against MDR A. hydrophila strain ZYAH75 and inhibited the biofilm on different food-contacting surfaces. ZPAH34 has a large dsDNA genome of 234 kb which belongs to a novel jumbo phage. However, its particle size is the smallest of known jumbo phages so far. Based on phylogenetic analysis, ZPAH34 was used to establish a new genus Chaoshanvirus. Biological characterization revealed that ZPAH34 exhibited wide environmental tolerance, and a high rapid adsorb and reproductive capacity. Food biocontrol experiments demonstrated that ZPAH34 reduces the viable count of A. hydrophila on fish fillets (2.31 log) and lettuce (3.28 log) with potential bactericidal effects. This study isolated and characterized jumbo phage ZPAH34 not only enriched the understanding of phage biological entity diversity and evolution because of its minimal virion size with large genome but also was the first usage of jumbo phage in food safety to eliminate A. hydrophila.

Characterization and protective effects of lytic bacteriophage pAh6.2TG against a pathogenic multidrug-resistant Aeromonas hydrophila in Nile tilapia (Oreochromis niloticus)

Bacteriophage (phage) is considered as one of the alternatives to antibiotics and an environmentally friendly approach to tackle antimicrobial resistance (AMR) in aquaculture. Here, we reported isolation, morphology and genomic characterizations of a newly isolated lytic phage, designated pAh6.2TG. Host range and stability of pAh6.2TG in different environmental conditions, and protective efficacy against a pathogenic multidrug-resistant (MDR) Aeromonas hydrophila in Nile tilapia were subsequently evaluated. The results showed that pAh6.2TG is a member of the new family Chaseviridae which has genome size of 51,780 bp, encoding 65 putative open reading frames (ORFs) and is most closely related to Aeromonas phage PVN02 (99.33% nucleotide identity). The pAh6.2TG was highly specific to A. hydrophila and infected 83.3% tested strains of MDR A. hydrophila (10 out of 12) with relative stability at pH 7-9, temperature 0-40°C and salinity 0-40 ppt. In experimental challenge, pAh6.2TG treatments significantly improved survivability of Nile tilapia exposed to a lethal dose of the pathogenic MDR A. hydrophila, with relative per cent survival (RPS) of 73.3% and 50% for phage multiplicity of infection (MOI) 1.0 and 0.1, respectively. Phage treatment significantly reduced the concentration of A. hydrophila in both water and fish body. Interestingly, the surviving fish from A. hydrophila challenged groups provoked specific antibody (IgM) against this bacterium. In summary, the findings suggested that the lytic phage pAh6.2TG is an effective alternative to antibiotics to control MDR A. hydrophila in tilapia and possibly other freshwater fish.

Ozone nanobubble treatments improve survivability of Nile tilapia (Oreochromis niloticus) challenged with a pathogenic multi-drug-resistant Aeromonas hydrophila

A rapid increase in multi-drug-resistant (MDR) bacteria in aquaculture highlights the risk of production losses due to diseases and potential public health concerns. Previously, we reported that ozone nanobubbles (NB-O₃ ) were effective at reducing concentrations of pathogenic bacteria in water and modulating fish immunity against pathogens; however, multiple treatments with direct NB-O₃ exposures caused alterations to the gills of exposed fish. Here, we set up a modified recirculation system (MRS) assembled with an NB-O₃ device (MRS-NB-O₃ ) to investigate whether MRS-NB-O₃ (a) were safe for tilapia (Oreochromis niloticus), (b) were effective at reducing bacterial load in rearing water and (c) improved survivability of Nile tilapia following an immersion challenge with a lethal dose of MDR Aeromonas hydrophila. The results showed no behavioural abnormalities or mortality of Nile tilapia during the 14-day study using the MRS-NB-O₃ system. In the immersion challenge, although high bacterial concentration (~2 × 10⁷  CFU/ml) was used, multiple NB-O₃ treatments in the first two days reduced the bacteria between 15.9% and 35.6% of bacterial load in water, while bacterial concentration increased from 13.1% to 27.9% in the untreated control. There was slight up-regulation of non-specific immune-related genes in the gills of the fish receiving NB-O₃ treatments. Most importantly, this treatment significantly improved survivability of Nile tilapia with relative percentage survival (RPS) of 64.7% - 66.7% in treated fish and surviving fish developed specific antibody against MDR A. hydrophila. In summary, the result suggests that NB-O₃ is a promising non-antibiotic approach to control bacterial diseases, including MDR bacteria, and has high potential for application in recirculation aquaculture system (RAS).

Isolation and characterization of bacteriophages against virulent Aeromonas hydrophila

Background

Aeromonas hydrophila is an important water-borne pathogen that leads to a great economic loss in aquaculture. Along with the abuse of antibiotics, drug-resistant strains rise rapidly. In addition, the biofilms formed by this bacterium limited the antibacterial effect of antibiotics. Bacteriophages have been attracting increasing attention as a potential alternative to antibiotics against bacterial infections.

Results

Five phages against pathogenic A. hydrophila, named N21, W3, G65, Y71 and Y81, were isolated. Morphological analysis by transmission electron microscopy revealed that phages N21, W3 and G65 belong to the family Myoviridae, while Y71 and Y81 belong to the Podoviridae. These phages were found to have broad host spectra, short latent periods and normal burst sizes. They were sensitive to high temperature but had a wide adaptability to the pH. In addition, the phages G65 and Y81 showed considerable bacterial killing effect and potential in preventing formation of A. hydrophila biofilm; and the phages G65, W3 and N21 were able to scavenge mature biofilm effectively. Phage treatments applied to the pathogenic A. hydrophila in mice model resulted in a significantly decreased bacterial loads in tissues.

Conclusions

Five A. hydrophila phages were isolated with broad host ranges, low latent periods, and wide pH and thermal tolerance. And the phages exhibited varying abilities in controlling A. hydrophila infection. This work presents promising data supporting the future use of phage therapy.

Novel Bacteriophages Capable of Disrupting Biofilms From Clinical Strains of Aeromonas hydrophila

The increase in global warming has favored growth of a range of opportunistic environmental bacteria and allowed some of these to become more pathogenic to humans. Aeromonas hydrophila is one such organism. Surviving in moist conditions in temperate climates, these bacteria have been associated with a range of diseases in humans, and in systemic infections can cause mortality in up to 46% of cases. Their capacity to form biofilms, carry antibiotic resistance mechanisms, and survive disinfection, has meant that they are not easily treated with traditional methods. Bacteriophage offer a possible alternative approach for controlling their growth. This study is the first to report the isolation and characterization of bacteriophages lytic against clinical strains of A. hydrophila which carry intrinsic antibiotic resistance genes. Functionally, these novel bacteriophages were shown to be capable of disrupting biofilms caused by clinical isolates of A. hydrophila. The potential exists for these to be tested in clinical and environmental settings.

Isolation and characterization of phage AHP-1 and its combined effect with chloramphenicol to control Aeromonas hydrophila

To develop an alternative bio-control measure for multi-drug resistant pathogenic Aeromonas hydrophila, which causes motile Aeromonas septicemia in fish, novel virulent phage (AHP-1) was isolated from carp tissues. Morphological analysis by transmission electron microscopy revealed that AHP-1 belongs to Myoviridae family. AHP-1 displayed 81% of moderate adsorption by 25 min, and latent period of 40 min with burst size of 97 PFU mL^-1 at an optimal multiplicity of infection (MOI) 0.1. AHP-1 was stable over a broad range of pH (4-11), temperature (4-50 °C), and salinity (0.1-3.5%). Both time and MOI dependent in vitro A. hydrophila growth inhibition was observed with AHP-1. AHP-1 (10 MOI) showed higher growth inhibition against A. hydrophila than chloramphenicol (5 μg mL^-1), and combined treatment was more promising than individuals. Immune gene expression analysis of zebrafish upon continuous bath exposure to AHP-1 resulted significantly higher (il-6 and sod-1) or slight induction (tnf-α, il1-β, il-10, and cxcl-8a) than controls at beginning of the phage exposure, but those lowered to basal level by day 12 post-phage exposure. It suggests no adverse immune responses have occurred for the AHP-1 dose that used, and have potential for the phage therapy. Further detailed in vivo studies are needed to confirm the protective efficacy of newly isolated AHP-1 against A. hydrophila infection.

Nine Novel Phages from a Plateau Lake in Southwest China: Insights into Aeromonas Phage Diversity

Aeromonas species are common pathogens of fish and some of them can opportunistically cause infectious diseases in humans. The overuse of antibiotics has led to the emergence of bacterial drug-resistance. To date, only 51 complete genome sequences of Aeromonas phages are available in GenBank. Here, we report the isolation of nine Aeromonas phages from a plateau lake in China. The protein cluster, dot plot and ANI analyses were performed on all 60 currently sequenced Aeromonas phage genomes and classified into nine clusters and thirteen singletons. Among the nine isolated phages, the DNA-packaging strategy of cluster 2L372D (including 2L372D, 2L372X, 4L372D, 4L372XY) is unknown, while the other five phages use the headful (P22/Sf6) DNA-packaging strategy. Notably, the isolated phages with larger genomes conservatively encode auxiliary metabolism genes, DNA replication and metabolism genes, while in smaller phage genomes, recombination-related genes were conserved. Finally, we propose a new classification scheme for Aeromonas phages.

Protective Effects of Bacteriophages against Aeromonas hydrophila Species Causing Motile Aeromonas Septicemia (MAS) in Striped Catfish

To determine the effectivity of bacteriophages in controlling the mass mortality of striped catfish (Pangasianodon hypophthalmus) due to infections caused by Aeromonas spp. in Vietnamese fish farms, bacteriophages against pathogenic Aeromonas hydrophila were isolated. A. hydrophila-phage 2 and A. hydrophila-phage 5 were successfully isolated from water samples from the Saigon River of Ho Chi Minh City, Vietnam. These phages, belonging to the Myoviridae family, were found to have broad activity spectra, even against the tested multiple-antibiotic-resistant Aeromonas isolates. The latent periods and burst size of phage 2 were 10 min and 213 PFU per infected host cell, respectively. The bacteriophages proved to be effective in inhibiting the growth of the Aeromonas spp. under laboratory conditions. Phage treatments applied to the pathogenic strains during infestation of catfish resulted in a significant improvement in the survival rates of the tested fishes, with up to 100% survival with MOI 100, compared to 18.3% survival observed in control experiments. These findings illustrate the potential for using phages as an effective bio-treatment method to control Motile Aeromonas Septicemia (MAS) in fish farms. This study provides further evidence towards the use of bacteriophages to effectively control disease in aquaculture operations.

Genomic Characterization of the Novel Aeromonas hydrophila Phage Ahp1 Suggests the Derivation of a New Subgroup from phiKMV-Like Family

Aeromonas hydrophila is an opportunistic pathogenic bacterium causing diseases in human and fish. The emergence of multidrug-resistant A. hydrophila isolates has been increasing in recent years. In this study, we have isolated a novel virulent podophage of A. hydrophila, designated as Ahp1, from waste water. Ahp1 has a rapid adsorption (96% adsorbed in 2 min), a latent period of 15 min, and a burst size of 112 PFU per infected cell. At least eighteen Ahp1 virion proteins were visualized in SDS-polyacrylamide gel electrophoresis, with a 36-kDa protein being the predicted major capsid protein. Genome analysis of Ahp1 revealed a linear doubled-stranded DNA genome of 42,167 bp with a G + C content of 58.8%. The genome encodes 46 putative open reading frames, 5 putative phage promoters, and 3 transcriptional terminators. Based on high degrees of similarity in overall genome organization and among most of the corresponding ORFs, as well as phylogenetic relatedness among their DNAP, RNAP and major capsid proteins, we propose a new subgroup, designated Ahp1-like subgroup. This subgroup contains Ahp1 and members previously belonging to phiKMV-like subgroup, phiAS7, phi80-18, GAP227, phiR8-01, and ISAO8. Since Ahp1 has a narrow host range, for effective phage therapy, different phages are needed for preparation of cocktails that are capable of killing the heterogeneous A. hydrophila strains.