PLASMID TRANSFER AND SEGREGATION IN LACTOBACILLUS-CURVATUS LTH1432 INVITRO AND DURING SAUSAGE FERMENTATIONS

The transfer and segregation of natural and recombinant plasmids in Lactobacillus curvatus LTH1432 were investigated in vitro, and during the fermentation of sausages. In vitro, the plasmids pAM-beta-1 and pNZ12 were maintained after 100 generations to 80 and 50%, respectively. Plasmids pCA44 and pIL253 were found in less than 5% of the cells isolated after 50 and 40 generations, respectively. During sausage fermentation, plasmids pAM-beta-1 and pNZ12 were present in more than 95% of the isolates from MRSS plates, whereas plasmids pCA44 and pIL253 were found in 50-80% of the isolates. The presence of plasmids pIL253 and pCA44 in L. curvatus LTH1432 resulted in a loss of the ability to compete with fortuitous meat borne strains. An influence of fortuitous antibiotic-resistant lactobacilli in meat with the in situ experiments can be excluded due to their very low numbers. Lactobacillus strains were isolated from the raw materials at frequencies of approx. 50 cells/g, which were resistant to chloramphenicol or erythromycin. To assess the potential of natural plasmid transfer among meat lactobacilli and to what extent it occurs in fermenting foods, a model system employing plasmid pAM-beta-1 was developed. In vitro, plasmid pAM-beta-1 was conjugally transferred from Enterococcus faecalis to L. curvatus LTH1432 and between strains of L. curvatus at frequencies of 2.1 x 10(-7) and 8 x 10(-6) transconjugants per recipient, respectively. in fermenting sausages, the transfer rate of plasmid pAM-beta-1 from L. curvatus LTH1432 (pAM-beta-1) to L. curvatus LTH1432 (pNZ12) was 1.3 x 10(-6) and hence, in the same order of magnitude as in vitro. With the model system described, first insights are provided in the behaviour of genetically modified starter organisms in fermenting foods.