THE GENE ENCODING THE LOW-AFFINITY PENICILLIN-BINDING PROTEIN 3R IN ENTEROCOCCUS-HIRAE S185R IS BORNE ON A PLASMID CARRYING OTHER ANTIBIOTIC-RESISTANCE DETERMINANTS

Two plasmid-derived NcoI DNA fragments of 14 and 4.5 kb, respectively, have been isolated from the multidrug-resistant strain Enterococcus h irae S185R and analyzed. The 14-kb fragment contains two inverted (L a nd R) IS1216 insertion modules of the ISS1 family. These modules defin e a Tn5466 transposon-like structure that contains one copy of the met hylase-encoding ermAM conferring erythromycin resistance and one copy of the adenylyl-transferase-encoding aadE conferring streptomycin resi stance. Immediately on the left side of IS1216L there occurs a copy of pbp3r encoding the low-affinity penicillin-binding protein (PBP) PBP3 r, itself preceded by a psr-like gene (psr3r) that controls the synthe sis of PBP3r. ermAM, aadE, and the transposase gene (tnp) of IS1216R h ave the same polarities, and these are opposite those of psr3r, pbp3r, and the tnp gene of IS1216L. The 4.5-kb fragment is a copy of the 4.5 -kb sequence at the 5' end of the 14-kb fragment, although it is not a restriction product of the 14-kb fragment. It contains three genes wi th the same polarity: psr3p, pbp3r, and tnp in an IS1216 element. Beca use of the very high degree of identity (99%) with the chromosomal psr fm and pbp5fm genes of Enterococcus faecium D63R, it is proposed that both the psr3r and pbp3r genes were transferred from E. faecium strain and inserted in a plasmid off. hirae. E. hirae is the first known bac terial species in which a low-affinity PBP-encoding gene has been foun d to be plasmid borne.