Evidence of incorporation of the chromosomal beta-lactamase gene of Enterococcus faecalis CH19 into a transposon derived from staphylococci.

We recently reported the chromosomal location of the staphylococcal beta-lactamase gene in four strains of Enterococcus faecalis. Transfer of this gene from strain CH19 to an enterococcal recipient was accompanied by transfer of numerous other antimicrobial resistance determinants in the absence of detectable plasmid DNA. A restriction map developed by comparing digestions of the regions surrounding the beta-lactamase gene in donor and recipient chromosomes resembles published maps of previously described staphylococcal beta-lactamase transposons, particularly in the area of the structural gene and its downstream region. In addition, DNA sequence analysis of the region immediately downstream of the beta-lactamase gene from both CH19 and its transcipient, CX19, revealed the presence of a 121-bp inverted repeat region found in Tn552 and Tn4002, two previously described staphylococcal beta-lactamase transposons. These results suggest that the chromosomal beta-lactamase gene of E. faecalis CH19 is incorporated into a transposonlike element derived from staphylococci.