Abstract
Edwardsiella ictaluri is an intracellular Gram-negative facultative pathogen causing enteric septicemia of catfish (ESC), a common disease resulting in substantial economic losses in the U.S. catfish industry. Previously, we demonstrated that several universal stress proteins (USPs) are highly expressed under in vitro and in vivo stress conditions, indicating their importance for E. ictaluri survival. However, the roles of these USPs in E. ictaluri virulence is not known yet. In this work, 10 usp genes of E. ictaluri were in-frame deleted and characterized in vitro and in vivo. Results show that all USP mutants were sensitive to acidic condition (pH 5.5), and EiΔusp05 and EiΔusp08 were very sensitive to oxidative stress (0.1% H2O2). Virulence studies indicated that EiΔusp05, EiΔusp07, EiΔusp08, EiΔusp09, EiΔusp10, and EiΔusp13 were attenuated significantly compared to E. ictaluri wild-type (EiWT; 20, 45, 20, 20, 55, and 10% vs. 74.1% mortality, respectively). Efficacy experiments showed that vaccination of catfish fingerlings with EiΔusp05, EiΔusp07, EiΔusp08, EiΔusp09, EiΔusp10, and EiΔusp13 provided complete protection against EiWT compared to sham-vaccinated fish (0% vs. 58.33% mortality). Our results support that USPs contribute E. ictaluri virulence in catfish.
Highlights
Enteric septicemia of channel catfish (ESC) is one of the most prevalent diseases of cultured catfish, causing significant losses (USDA, 2014)
In-frame deletion resulted in removal of a large portion (86–99%) of the wild-type usp genes (Table 3)
The growth of E. ictaluri wild-type (EiWT) and universal stress proteins (USPs) mutants in Brain Heart Infusion (BHI) broth indicated that Ei usp03 and Ei usp04 have a significantly (p < 0.001) higher growth rate than EiWT
Summary
Enteric septicemia of channel catfish (ESC) is one of the most prevalent diseases of cultured catfish, causing significant losses (USDA, 2014). One of the earliest clinical signs of ESC is reduced appetite. These antimicrobials are only useful in limiting the spread of an outbreak and rather than treating the disease. The universal stress proteins (USP) have a conserved domain of 140–160 amino acids, and are present in archaea, bacteria, and plants (Nachin et al, 2005), but not in animals and human (Siegele, 2005). The uspA mutation caused decreased survival in E. coli (Tkaczuk et al, 2013). USPs affect persistence and survival of Mycobacterium tuberculosis (Hingley-Wilson et al, 2010), and cause growth arrest and reduce the virulence in Edwardsiella ictaluri Universal Stress Proteins
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