Lytic phage vB_AdhP_L12 against Aeromonas dhakensis from crocodiles: Characterization and safety

Le résumé fourni par la source

Aeromonas dhakensis ( A. dhakensis ), a highly virulent and multidrug-resistant zoonotic pathogen, poses a severe threat to the sustainable development of aquaculture (e.g., crocodile farming) and food safety. In this study, we aimed to develop an antibiotic-alternative prevention and control strategy. To this end, we isolated a phage vB_AdhP_L12 with strong lytic activity against A. dhakensis from general hospital domestic sewage. Morphological observation and phylogenetic analysis identified vB_AdhP_L12 as a novel phage belonging to the genus Teseptimavirus in the family Autographiviridae , which is characterized by an icosahedral head and a short, non-contractile tail. Environmental stability assays demonstrated that vB_AdhP_L12 maintained stable activity at temperatures ranging from −20 °C to 37 °C and pH values ranging from 4 to 11 and exhibited tolerance to low concentrations of chloroform, indicating its suitability for aquaculture environments. Host range determination revealed that it specifically lysed eight strains of A. dhakensis isolated from crocodiles, with no activity against other common aquatic bacterial strains. Whole-genome sequencing revealed that the phage has a linear double-stranded DNA genome of 38,749 bp, containing 42 open reading frames and lacks antibiotic resistance genes, virulence factors, and lysogeny-related genes, confirming its high level of biosafety. In vitro experiments confirmed that vB_AdhP_L12 exhibited optimal bacteriostatic effects at a multiplicity of infection of 0.01, efficiently lysing A. dhakensis and protecting Caco-2 and EPC cells from damage. In the zebrafish infection model, immersion treatment with vB_AdhP_L12 resulted in a survival rate of 63.33% in the experimental group, with a significant reduction in mortality. Moreover, pathological damage to intestinal tissues was effectively repaired. Quantitative PCR results revealed that the overexpression of pro-inflammatory cytokines was markedly suppressed, while the levels of anti-inflammatory cytokines and specific antibodies were significantly upregulated. These findings indicate that phage immersion treatment can modulate the host immune response to a certain extent. Nevertheless, whether such immunomodulatory effects arise directly from phage–host interactions or represent a secondary consequence of bacterial clearance remains to be further explored. In conclusion, phage vB_AdhP_L12 has several advantages, including strong host specificity, excellent environmental adaptability, high biosafety, and significant in vitro and in vivo therapeutic efficacies. This study provides a novel technical prototype for the sustainable prevention and control of A. dhakensis infections in crocodile farming, serving as a promising antibiotic alternative with strong potential for translation to aquaculture practice. This study is of critical significance for alleviating the antibiotic resistance crisis and ensuring the safety of aquaculture.

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