Interpretive criteria to differentiate low- and high-level mupirocin resistance in Staphylococcus aureus

Meticillin-resistant Staphylococcus aureus isolates were classified into three mupirocin susceptibility groups by the disc diffusion method using 5 and 200 microg mupirocin discs. The zone diameter observed for a 5 microg disc distinguished Mup(S) from the resistant strains (either Mup(RL) or Mup(RH)). On the other hand, a 200 microg disc distinguished the high-resistance Mup(RH) strains from the other two (Mup(S) or Mup(RL)). Thus, the concomitant use of 5 and 200 microg mupirocin discs allowed the clear distinction among the three mupirocin susceptibility groups, Mup(S), Mup(RL) or Mup(RH).