ENHANCED CONJUGATIVE TRANSFER OF PLASMID DNA FROM ESCHERICHIA-COLI TOSTAPHYLOCOCCUS-AUREUS AND LISTERIA-MONOCYTOGENES

Transfer of mobilizable shuttle cloning vectors by conjugation from Es cherichia coli to Staphylococcus aureus occurred at a very low frequen cy (10(-9) transconjugants per donor colony-forming unit after the mat ing period). It was observed that subinhibitory concentrations of peni cillins (oxacillin or penicillin G) in the mating medium resulted in i ncreased transfer frequency by conjugation of the shuttle vector pAT18 from E. coli SM10 to S. aureus 80CR5 Str (54-fold) and to Listeria mo nocytogenes L017RF (45-fold). These results were interpreted as indica ting that the cell wall of Gram-positive bacteria constitutes an impor tant barrier for conjugative transfer of genetic information delivered from E. coli. It was also demonstrated that presence of a restriction system(s) in S. aureus recipients represented a major barrier to intr oduction of foreign DNA.