Evaluation of protective efficacy of a novel Aeromonas phage PAS-1 against A. salmonicida subsp. salmonicida infections in rainbow trout (Oncorhynchus mykiss) model

Abstract

To search for candidate control agents against antibiotic-resistant A. salmonicida subsp. salmonicida infections in salmonid culture, one lytic bacteriophage (phage), designated as PAS-1, was isolated from the environmental water, and its several biological properties were investigated. The phage showed broad host ranges to other subspecies of A. salmonicida as well as A. salmonicida subsp. salmonicida including antibiotic-resistant strains. The PAS-1 was morphologically classified as Myoviridae and possessed approximately 48 kb of double-strand genomic DNA. Moreover, partial genomic and structural proteomic analysis of PAS-1 revealed that the phage was closely related to other Myoviridae phages infecting Enterobacteriaceae or Aeromonadaceae. For the evaluation of potential protective efficacy of PAS-1, the phage was preferentially co-cultured with one virulent A. salmonicida subsp. salmonicida strain that possesses the ascV gene, and strong bacteriolytic activity was observed against the bacteria. The administration of PAS-1 in rainbow trout (Oncorhynchus mykiss) demonstrated that it was cleared within 200 h post-administration from the fish kidneys, and temporal neutralizing activity against the phage was detected in the phage-administrated fish serums. The protective effects of the phage were verified in experimental rainbow trout-furunculosis model therapy, showing increased survival rates and mean time to death.everal biological properties were investigated. The phage showed broad host ranges to other subspecies of A. salmonicida as well as A. salmonicida subsp. salmonicida including antibiotic-resistant strains. The PAS-1 was morphologically classified as Myoviridae and possessed approximately 48 kb of double-strand genomic DNA. Moreover, partial genomic and structural proteomic analysis of PAS-1 revealed that the phage was closely related to other Myoviridae phages infecting Enterobacteriaceae or Aeromonadaceae. For the evaluation of potential protective efficacy of PAS-1, the phage was preferentially co-cultured with one virulent A. salmonicida subsp. salmonicida strain that possesses the ascV gene, and strong bacteriolytic activity was observed against the bacteria. The administration of PAS-1 in rainbow trout (Oncorhynchus mykiss) demonstrated that it was cleared within 200 h post-administration from the fish kidneys, and temporal neutralizing activity against the phage was detected in the phage-administrated fish serums. The protective effects of the phage were verified in experimental rainbow trout-furunculosis model therapy, showing increased survival rates and mean time to death.