Mixed serotype expression in a novel vaccine strain of Vibrio cholerae

Abstract

Cholera is a severe disease that exists all over the world but mostly in developing countries. Currently available oral vaccines are effective but are complicated to make and therefore relatively expensive. The vaccine comes in liquid form an requires both a cold chain for distribution and two doses for full protection. If a more effective and cheaper vaccine that requires only a single dose for full protection could be developed in a dry formulation, it would have a potentially profound effect in developing countries. This study is a part of a larger project that aims to generate a single vaccine strain. During the limited time available in this study neither of the two methods, In vitro transposition and red/gam recombination system, used for introducing mutations into the genome of Vibrio cholerae was successfully developed. However the genes are cloned and standard suicide vector mutagenesis can proceed in further studies. It has been demonstrated that when a wbeT-gene from an Ogawa strain are inserted in trans in an Inaba strain, and the levels of expression are limited, the result is a culture that expresses both Ogawa and Inaba serotypes. Immunisation studies are ongoing. There is interest in developing the red/gam recombination system for Vibrio cholerae, since it is more straightforward and simpler than the traditional methods. However, additional studies and more time are needed to investigate why the recombination system did not work and how to make it functional in Vibrio cholerae. The results indicate the described approach to make mixed serotype strains is valid but more studies are also needed to determine if the culture that expresses both serotypes consists of cells that express both serotypes or if it is a mixture of cells each expressing a single serotype. Strains for the experiment are available and with FACS it is easily demonstrated.