Safety aspects of genetically modified lactic acid bacteria

Lactic acid bacteria (LAB) are in several ways related to human life among which their contribution to virtually all processes of food fermentations is of special importance. The safe nature of the organisms involved is known from experience and genetic modifications have to keep this status unchanged. To improve the technological and beneficial potential of LAB, genetic modification has been applied to these organisms. The majority of studies was devoted to lactococci with applications in the dairy field. With these organisms the development of food grade systems for genetic modification has become most advanced employing chromosomal gene integration and food grade vectors. Lactobacilli have broadest application in the various fields of food processing but comparatively little is known on their genetics. In studies with strains of Lactobacillus sake and Lactobacillus curvatus suitable as starters in meat fermentation, we studied the behavior of modified strains containing genes coding for useful properties such as formation of catalase and lysostaphin. The investigation of the stability of the constructs and of horizontal gene transfer was performed in vitro and in fermenting sausages. It was observed that the constructs retained their acquired metabolic activity and no gene transfer could be detected. On the other hand, the fermentation substrates permit efficient gene transfer as it was indicated by the transfer of the conjugative plasmid pAMD1.