Analysis of the vaccine potential of a laboratory Escherichia coli strain in a Japanese flounder model.

Escherichia coli DH5alpha is a genetically tailored laboratory strain that is commonly used for general cloning. In this study, the vaccine potential of DH5alpha was investigated. It was found that when used as a live vaccine, DH5alpha could afford effective protection upon Japanese flounder against Aeromonas hydrophila infection. Vaccination with purified outer membrane proteins and lipopolysaccharides of DH5alpha failed to induce protective immunity against A. hydrophila. Specific antibody production was observed in fish immunized with DH5alpha, which lasted at least 8 weeks and was enhanced by a booster injection during the vaccination process. Analysis of the transcription profiles of immune-related genes showed that vaccination with DH5alpha heightened the expression of the genes encoding factors that are likely involved in both specific and nonspecific immunities. Furthermore, compared to the control fish, fish vaccinated with DH5alpha/pAQ1, which is DH5alpha harboring the plasmid pAQ1 that expresses the coding element of a Vibrio harveyi antigen, exhibited significantly improved survival rates following V. harveyi and A. hydrophila challenges. These results demonstrate that DH5alpha possesses intrinsic immunoprotective potential against A. hydrophila. This property, together with the feature of cloning friendliness, should render DH5alpha useful in the construction of cross-protective vaccines.