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

Abstract

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.

Bacteriophages in the Control of Aeromonas sp. in Aquaculture Systems: An Integrative View

“…are affected by A. hydrophila . The high mortality, weight loss and high treatment costs lead to severe economic losses to the aquaculture industry [ 6 , 92 , 93 , 94 , 95 , 96 ].…”

“…Furthermore, they do not always offer full protection and can be very difficult to administer by injection [ 6 ]. As such, the application of virulent phages to prevent and/or treat infections appears as a promising strategy [ 51 , 91 , 94 , 148 , 149 , 150 ], at a time when more efficient approaches are needed to control Aeromonas diseases.…”

“…Several studies have analyzed phenotypic and genotypic characterization, and evaluated the effectiveness of phages against A. hydrophila , including phages pAh1-C and pAh6-C [ 209 ]; Ahp1 [ 210 ]; pAh-1 [ 211 ]; Φ2 [ 95 ]; AP1, AP2, AP3 and AP4 [ 92 ]; CT45P and TG25P [ 212 ]; MJG [ 91 ], AHP-1 [ 181 ]; Akh-2 [ 149 ], PVN-02 [ 148 , 213 ], AhyVDH1 [ 214 ] and pAh6.2T [ 94 ] ( Tables S2 and S3 ). Previous studies have shown that phages can be used to biocontrol A. hydrophila infections in loach ( M. anguillicaudatus ) [ 149 , 174 , 209 ], Nile tilapia ( O. niloticus ) [ 92 , 93 ], striped catfish ( P. hypophthalmus ) [ 95 , 148 ] and rainbow trout ( O. mykiss ) [ 91 , 94 ] ( Table S3 ).…”

“…Cao et al (2020) administered phage MJG by injection, immersion and oral administrations to control A. hydrophila in rainbow trout and achieved a relative percent survival of 100%, 66.7%, and 50%, respectively [ 91 ]. Additionally, Dien et al (2021) showed that treatments with phage pAh6.2TG significantly improved survivability of Nile tilapia exposed to lethal doses of A. hydrophila (10 7 CFU/mL), with relative percent survival of 73.3% and 50% at an MOI of 1.0 and 0.1, respectively [ 94 ].…”

“…In general, phages are highly specific, infecting only one bacterial genus or even particular strains [ 224 ]. Most Aeromonas phages showed narrow host specificity, infecting only the original host bacterium [ 51 , 93 , 150 , 214 ] or strains of a given bacterial species [ 91 , 94 , 95 , 149 , 209 , 220 , 230 , 231 ] ( Table S2 ). The majority of marine phages are highly host-specific [ 232 , 233 , 234 ], and about 73% lyse only the original host bacterium [ 234 ].…”