A DYADIC PLASMID THAT SHOWS MLS AND PMS RESISTANCE IN STAPHYLOCOCCUS-AUREUS

Out of a collection of 56 Staphylococcus aureus clinical strains from 1971 to 1990 in Japan, we found one 1971 isolate, strain MS8968, harbo ring plasmid pMS97. A transductant strain, MS15009(pMS97), showed indu cible resistance to a group of drugs, the so-called MLS antibiotics in the presence of a low concentration of erythromycin (EM). However, in the case of oleandomycin (OL), the strain showed resistance to anothe r group of antibiotics: 14-membered macrolides (EM and OL), a 16-membe red macrolide (mycinamicin I), and type B streptogramin, the so-called PMS antibiotics. Moreover, plasmid pMS97 contained an erm gene with u niversal primers specific for erm A, AM, B, BC, C, C', and G and an ms rA gene with primers specific for msrA. The first finding suggests tha t two genes encoding functionally different mechanisms for MLS and PMS resistance, erm and msrA, are present together within plasmid pMS97 o riginating from S. aureus.