Phenotype, virulence and immunogenicity of Edwardsiella ictaluri cyclic adenosine 3′,5′-monophosphate receptor protein (Crp) mutants in catfish host

Abstract

Edwardsiella ictaluri is an Enterobacteriaceae that causes lethal enteric septicemia in catfish. Being a mucosal facultative intracellular pathogen, this bacterium is an excellent candidate to develop immersion-oral live attenuated vaccines for the catfish aquaculture industry. Deletion of the cyclic 3′,5′-adenosine monophosphate (cAMP) receptor protein ( crp) gene in several Enterobacteriaceae has been utilized in live attenuated vaccines for mammals and birds. Here we characterize the crp gene and report the effect of a crp deletion in E. ictaluri. The E. ictaluri crp gene and encoded protein are similar to other Enterobacteriaceae family members, complementing Salmonella enterica Δ crp mutants in a cAMP-dependent fashion. The E. ictaluri Δ crp-10 in-frame deletion mutant demonstrated growth defects, loss of maltose utilization, and lack of flagella synthesis. We found that the E. ictaluri Δ crp-10 mutant was attenuated, colonized lymphoid tissues, and conferred immune protection against E. ictaluri infection to zebrafish ( Danio rerio) and catfish ( Ictalurus punctatus). Evaluation of the IgM titers indicated that bath immunization with the E. ictaluri Δ crp-10 mutant triggered systemic and skin immune responses in catfish. We propose that deletion of the crp gene in E. ictaluri is an effective strategy to develop immersion live attenuated antibiotic-sensitive vaccines for the catfish aquaculture industry.