Phenotype, Virulence and Immunogenicity of Edwardsiella piscicida Cyclic AMP Receptor Protein (Crp) Mutants in Catﬁsh Host.

Peng Zhou,Xueqing Han,Yang Zhou,Yong-An Zhang,Quan Xie,Ting Yan,Feifei Zheng,Xiang Ye,Roy Curtiss

doi:10.3390/microorganisms8040517

Peng Zhou, Xueqing Han + Show 7 more

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https://doi.org/10.3390/microorganisms8040517

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Edwardsiella piscicida, a facultative aerobic pathogen belonging to the Enterobacteriaceae family, is the etiological agent of edwardsiellosis that causes significant economic loses in the aquaculture industry. cAMP receptor protein (CRP) is one of the most important transcriptional regulators, which can regulate large quantities of operons in different bacteria. Here we characterize the crp gene and report the effect of a crp deletion in E. piscicida. The crp-deficient mutant lost the capacity to utilize maltose, and showed significantly reduced motility due to the lack of flagella synthesis. We further constructed a ΔPcrp mutant to support that the phenotype above was caused by the crp deletion. Evidence obtained in fish serum killing assay and competitive infection assay strongly indicated that the inactivation of crp impaired the ability of E. piscicida to evade host immune clearance. More importantly, the virulence of the crp mutant was attenuated in both zebrafish and channel catfish, with reductions in mortality rates. In the end, we found that crp mutant could confer immune protection against E. piscicida infection to zebrafish and channel catfish, indicating its potential as a live attenuated vaccine.

Highlights

Edwardsiella piscicida is a facultative anaerobe and Gram-negative enteric pathogen that generally causes lethal edwardsiellosis, which is a systematic enterohemorrhagic septicemic disease that can lead to high stock mortality in fresh and marine fish [1,2]
cyclic AMP receptor protein (Crp) genes in enteric fish pathogens including two Aeromonas species and two Edwardsiella species showed close genetic relationship according to this phylogenetic tree
The E. piscicida Crp 3-D predicted structure exhibits the flexible hinge required for Crp dimerization and the F-helix & C-helix that interacts with the DNA (Figure 2B)

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Edwardsiella piscicida is a facultative anaerobe and Gram-negative enteric pathogen that generally causes lethal edwardsiellosis, which is a systematic enterohemorrhagic septicemic disease that can lead to high stock mortality in fresh and marine fish [1,2]. Antibiotic abuse represents a problematic method of treating bacterial infections in the aquaculture industry and has led to the evolution of multi-drug resistance strains [5]. Plasmid-mediated multi-drug resistant has been previously reported in E. piscicida [6]. In response to this potential, vaccination is an important disease control strategy that has significantly contributed to reduction of outbreaks and antibiotics use in aquaculture [7]. It is worth noting that intracellular bacterial vaccines evoke cellular mediated immune responses that “kill” and eliminate infected cells [7]. The intracellular lifestyle of E. piscicida has been gradually revealed. This pathogen could successfully survive and replicate within fish phagocytes [8]. The above attributes make E. piscicida a promising candidate to be developed as a live attenuated vaccine against edwardsiellosis

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