Tissue Persistence and Vaccine Efficacy of an O Polysaccharide Mutant Strain of Edwardsiella ictaluri

Abstract

AbstractStudies were conducted to determine the tissue persistence and vaccine efficacy of a previously constructed isogenic O polysaccharide (OPS) mutant strain (93–146 R6) of the bacterium Edwardsiella ictaluri in channel catfish Ictalurus punctatus. The OPS‐negative strain retained the ability to infect channel catfish following immersion exposure and persisted in the trunk kidney at least 14 d, whereas previously reported attenuated E. ictaluri strains were cleared by 72 h postexposure. Vaccination with 93–146 R6 by intraperitoneal injection provided significant protection against subsequent immersion challenge with the virulent parental strain, but vaccination by immersion did not provide protection. The commercial vaccine RE‐33 provided significant protection when fish were vaccinated by immersion, but RE‐33 was more virulent than 93–146 R6 when given by intraperitoneal injection.