AUTHOR=Abdelhamed Hossam , Lawrence Mark L. , Karsi Attila 

TITLE=Development and Characterization of a Novel Live Attenuated Vaccine Against Enteric Septicemia of Catfish

JOURNAL=Frontiers in Microbiology

VOLUME=9

YEAR=2018

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2018.01819

DOI=10.3389/fmicb.2018.01819

ISSN=1664-302X

ABSTRACT=<p><italic>Edwardsiella ictaluri</italic> is a Gram-negative intracellular pathogen causing enteric septicemia of channel catfish (ESC). Type six secretion system (T6SS) is a sophisticated nanomachine that delivers effector proteins into eukaryotic host cells as well as other bacteria. In the current work, we in-frame deleted the <italic>E. ictaluri</italic><italic>evpB</italic> gene located in the T6SS operon by allelic exchange. The safety and efficacy of <italic>Ei</italic>Δ<italic>evpB</italic> as well as Aquavac-ESC, a commercial vaccine manufactured by Intervet/Merck Animal Health, were evaluated in channel catfish (<italic>Ictalurus punctatus</italic>) fingerlings and fry by immersion exposure. Our results showed that the <italic>Ei</italic>Δ<italic>evpB</italic> strain was avirulent and fully protective in catfish fingerlings. The <italic>Ei</italic>Δ<italic>evpB</italic> strain was also safe in catfish fry, and immersion vaccination with <italic>Ei</italic>Δ<italic>evpB</italic> at doses 10<sup>6</sup> and 10<sup>7</sup> CFU/ml in water resulted in 34.24 and 80.34% survival after wild-type immersion challenge compared to sham-vaccinated fry (1.79% survival). Catfish fry vaccinated with <italic>Ei</italic>Δ<italic>evpB</italic> at doses 10<sup>6</sup>, 10<sup>7</sup>, and 10<sup>8</sup> CFU/ml in water exhibited dose-dependent protection. When compared with Aquavac-ESC, <italic>Ei</italic>Δ<italic>evpB</italic> provided significantly higher protection in catfish fingerlings and fry (<italic>p</italic> &lt; 0.05). Results indicate that the <italic>Ei</italic>Δ<italic>evpB</italic> strain is safe and can be used to protect catfish fingerlings and fry against <italic>E. ictaluri</italic>.</p>