Construction and Characterization of an Aeromonas hydrophila Multi-Gene Deletion Strain and Evaluation of Its Potential as a Live-Attenuated Vaccine in Grass Carp.

Jihong Li,Md Sharifull Islam,Wei Yu,Xiang Ye,Yang Zhou,Peng Zhou,Yong-An Zhang,Jinquan Li,Zhi Li,Shilin Ma

doi:10.3390/vaccines9050451

Jihong Li, Md Sharifull Islam + Show 8 more

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https://doi.org/10.3390/vaccines9050451

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Abstract

Aeromonas hydrophila is an important pathogen that causes motile Aeromonas septicemia (MAS) in the aquaculture industry. Aerolysin, hemolysin, serine protease and enterotoxins are considered to be the major virulence factors of A. hydrophila. In this study, we constructed a five-gene (aerA, hly, ahp, alt and ast) deletion mutant strain (named Aeromonas hydrophila five-gene deletion strain, AHFGDS) to observe the biological characteristics and detect its potential as a live-attenuated vaccine candidate. AHFGDS displayed highly attenuated and showed increased susceptibility to fish blood and skin mucus killing, while the wild-type strain ZYAH72 was highly virulent. In zebrafish (Danio rerio), AHFGDS showed a 240-fold higher 50% lethal dose (LD50) than that of the wild-type strain. Immunization with AHFGDS by intracelomic injection or immersion routes both provided grass carp (Ctenopharyngodon idella) significant protection against the challenge of the strain ZYAH72 or J-1 and protected the fish organs from serious injury. Further agglutinating antibody titer test supported that AHFGDS could elicit a host-adaptive immune response. These results suggested the potential of AHFGDS to serve as a live-attenuated vaccine to control A. hydrophila infection in aquaculture.

Highlights

Introduction iationsThe ubiquitous bacterium Aeromonas hydrophila is an important Gram-negative, motile, rod-shaped bacterium belonging to the class of Gammaproteobacterias, order Aeromonadales and family Aeromonadaceae [1]
The results showed that when immunized either by immersion or by injection route, AHFGDS can induce high levels of protection against A. hydrophila infection in grass carp
To generate a fully attenuated live vaccine strain, we constructed the mutant with deletion in the region covering the genes ast, alt, ahp, hly and Aerolysin A (aerA) that play important roles in the bacterial pathogenesis

Summary

Introduction

The ubiquitous bacterium Aeromonas hydrophila is an important Gram-negative, motile, rod-shaped bacterium belonging to the class of Gammaproteobacterias, order Aeromonadales and family Aeromonadaceae [1]. A. hydrophila can infect a wide variety of freshwater and marine fish, causing motile Aeromonas septicemia (MAS) [2]. MAS affects different fish species, including tilapia (Oreochromis niloticus), catfish (Ictalrus punctatus), goldfish (Carassius auratus), common carp (Cyprinus carpio L.). Eel (Anguilla spp.), which causes severe economic losses to the aquaculture industry through high mortality, weight loss and high treatment costs [4]. Grass carp (Ctenopharyngodon idella) is a fish species of the largest production in the world, accounting for ~16% of global freshwater aquaculture, and is an important economic species farmed extensively in Licensee MDPI, Basel, Switzerland.

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