Analysis of the effect of copper on the virulence of a pathogenic Edwardsiella tarda strain

Aim: To investigate the effect of copper on the virulence of Edwardsiella tarda. Methods and Results: The pathogenic Edw. tarda strain TX5 was cultured under copper-stressed conditions and examined for any potential alteration in capacities that are associated with pathogenicity. The results showed that compared to untreated TX5, Cu-treated TX5 exhibits reduced planktonic and biofilm growth, an impaired ability to adhere to host mucus, modulation of host immune response, and dissemination in host blood and liver. Consistent with these observations, the overall bacterial virulence of Cu-treated TX5 is significantly attenuated. SDS-PAGE analyses of whole cell protein production showed that Cu-treated TX5 differs from the untreated TX5 in its production of at least one protein. Quantitative real time reverse transcriptase PCR analyses showed that copper treatment decreased the expression of virulence-associated genes encoding components of the type III and type VI secretion systems, the Eth haemolysin system, and the LuxS/AI-2 quorum-sensing system. Conclusions: Prolonged exposure to copper has multiple effects on TX5 and results in significant attenuation of bacterial virulence. Significance and Impact of the Study: The results of this study demonstrate that copper treatment has a broad and profound effect on the virulence-associated capacities of TX5, which is exerted at least in part at the transcription level. These findings provide new insights to the antimicrobial mechanism of copper.