Mupirocin Resistance Screening of Methicillin-Resistant Staphylococcus aureus Isolates at Madigan Army Medical Center

Abstract

Mupirocin is an antibiotic used for eradication and infection control of methicillin-resistant Staphylococcus aureus (MRSA). Mupirocin binds to the bacterial isoleucyl tRNA synthetase, thus disrupting bacterial protein synthesis. Four hundred nine MRSA clinical isolates collected in 2006 and 2007 at Madigan Army Medical Center were screened for mupirocin resistance by E test and polymerase chain reaction; 7 MRSA isolates (1.7%) were found to be fully resistant to mupirocin (minimum inhibitory concentration [MIC] by E test: >1,024 µg/mL), 10 isolates (2.4%) had MIC values of 1 to 32 µg/mL, while 392 MRSA isolates (95.9%) had MIC values of <1 µg/mL. No trend of increased mupirocin resistance was found when compared with subsequent years. These results show that mupirocin remains a valid infection control measure due to its unique mechanism of action and the high susceptibility rate of MRSA isolates. In addition, rapid screening by polymerase chain reaction of MRSA shows promise in assessing the fully resistant mupirocin phenotype.