Susceptibility of staphylococci isolated from a burns unit to mupirocin and other antimicrobial agents

Abstract

The activity of mupirocin (Bactroban) against coagulase-positive and coagulase-negative staphylococci isolated in a burns unit was tested to ascertain its effectiveness, and to detect any resistant isolates after continuous use of mupirocin for 2.5 years. A total of 395 staphylococci, consisting of 330 Staphylococcus aureus and 65 coagulase-negative staphylococci, were tested for resistance to mupirocin and other antimicrobial agents. The results showed that 94.5% of the isolates were fully susceptible to mupirocin (MIC ≤4 mg/l), and 5.3% expressed low-level resistance (MIC 8-128 mg/l). One Staphylococcus haemolyticus isolate expressed high-level resistance (MIC >1,024 mg/l). It transferred high-level mupirocin resistance to other staphylococci in conjugation experiments, which indicated a capacity to transmit mupirocin resistance between species. The results demonstrated that mupirocin was still highly effective against staphylococci in the burns unit. However, the demonstration that the resistant S. haemolyticus isolate could transfer high-level mupirocin resistance to other staphylococci was of concern. There is a compelling need to test staphylococci from clinical materials for mupirocin resistance. Early detection of resistance can prevent the establishment and spread of the mupirocin-resistant strains in the unit.