Assessment of horizontal gene transfer in Lactic acid bacteria--a comparison of mating techniques with a view to optimising conjugation conditions.

Plate, filter and broth mating techniques were assessed over a range of pHs using three Lactococcus lactis donor strains (one with an erythromycin resistance marker and two with tetracycline resistance markers, all located on transferable genetic elements) and one L. lactis recipient strain. Transconjugants were confirmed using antibiotic selection, E-tests to determine MICs, PCR assays to detect the corresponding marker genes, DNA fingerprinting by pulsed-field gel electrophoresis (PFGE), and Southern blotting. Horizontal gene transfer (HGT) rates varied (ranging from 1.6 x 10(-1) to 2.3 x 10(-8)). The general trend observed was plate > filter > broth, independent of pH. Our data suggests that standardisation of methodologies to be used to assess HGT, is warranted and would provide a meaningful assessment of the ability of commensal and other bacteria in different environments to transfer relevant markers.