Abstract
Phage therapy can be an effective alternative to standard antimicrobial chemotherapy for control of Aeromonas hydrophila infections in aquaculture. Aeromonas hydrophila-specific phages AhMtk13a and AhMtk13b were studied for basic biological properties and genome characteristics. Phage AhMtk13a (Myovirus, 163,879 bp genome, 41.21% CG content) was selected based on broad lytic spectrum and physiologic parameters indicating its lytic nature. The therapeutic potential of phage AhMtk13a was evaluated in experimental studies in zebrafish challenged with A. hydrophila GW3-10 via intraperitoneal injection and passive immersion in aquaria water. In experimental series 1 with single introduction of AhMtk13a phage to aquaria water at phage–bacteria ratio 10:1, cumulative mortality 44% and 62% was registered in fish exposed to phage immediately and in 4 h after bacterial challenge, correspondingly, compared to 78% mortality in the group with no added phage. In experimental series 2 with triple application of AhMtk13a phage at ratio 100:1, the mortality comprised 15% in phage-treated group compared to the 55% in the control group. Aeromonas hydrophila GW3-10 was not detectable in aquaria water from day 9 but still present in fish at low concentration. AhMtk13a phage was maintained in fish and water throughout the experiment at the higher concentration in infected fish.
Highlights
The aquaculture industry has been expanding significantly worldwide in the past decades
This study aimed at the detailed characterization of two new A. hydrophila specific phages and evaluation of their potential for infection control in aquaculture
Forty-nine Aeromonas strains were used in this study: 46 Georgian strains, majority collected from sick fish and water in 5 fish farms in Central Georgia, including 39 strains of A. hydrophila, 5 strains of A. caviae, and 2 strains A. sobria
Summary
The aquaculture industry has been expanding significantly worldwide in the past decades. In 2018, total fish production, trade, and consumption reached an all-time record equaling 114.5 million tons in live weight [1]. Aquaculture is one of the fastest growing and developing sectors in South Caucasus region, including Georgia. Rainbow trout is the most common cultured fish species in Georgia, comprising 61% of the total fish production [2]. One of the main challenges for the development of aquaculture worldwide and in Georgia are bacterial infections that may lead to massive death in fish and, correspondingly, to large financial losses. The problem related to occurrence and spread of infections is especially acute for fish hatcheries and larvae producing facilities, and juvenile fish ponds, where mortality rates usually are significantly higher compared to adult fish
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