Detection of methicillin-resistant Staphylococcus aureus with high-level resistance to mupirocin.

Staphylococcus aureus with high-level mupirocin resistance has rarely been isolated in Japan. We detected methicillin-resistant S. aureus (MRSA) with high-level mupirocin resistance (HLMR-MRSA; MIC ≥1,024 μg/ml) in a surveillance program of invasive MRSA infection in the Minami Ibaraki Area of Japan. The other 177 strains surveyed in the program showed susceptibility or low-level resistance to mupirocin. The HLMR-MRSA strain, named 115, was isolated from the blood of a patient with peripheral venous catheter-associated infection. The patient had not received administration of mupirocin before the isolation of strain 115. Another HLMR-MRSA strain, named 257, was recovered from the patient's sputum obtained 1 year after the infection. Close relatedness between genotypes of strains 115 and 257 indicated persistent colonization of strain 115 on the patient. In contrast, no HLMR-MRSA was detected in materials submitted from other inpatients treated in the same wards during the same period, demonstrating that horizontal transmission of HLMR-MRSA did not occur.