Comparison of enterococcal and staphylococcal beta-lactamase-encoding fragments.

A restriction map of a 13.5-kb EcoRI fragment encoding beta-lactamase from a plasmid isolated from enterococcal strain PA was prepared and found to differ markedly from the published maps of beta-lactamase-encoding EcoRI fragments of two staphylococcal plasmids and the plasmid from enterococcal strain HH22. This comparison also showed that one of two contiguous EcoRV fragments that encompass the beta-lactamase gene differs in size in the PA strain from that found in the other strains. However, restriction sites in the beta-lactamase structural gene (blaZ) were identical in all four plasmids. Further studies compared the beta-lactamase genes of four clinical enterococcal isolates from various geographic locations with those described above. Isolates from Virginia and Florida generated EcoRV fragments identical to those from the plasmid from strain PA, while isolates from Lebanon and Argentina showed EcoRV fragments analogous to those from HH22 and the staphylococci studied. Although there is evidence suggesting that some of these beta-lactamase-producing enterococcal isolates represent a single strain, this study indicates that there is significant variation in the plasmids that encode beta-lactamase.