[Investigation of mupirocin resistance in nosocomial methicillin-resistant Staphylococcus aureus isolates by phenotypic and genotypic methods]

Abstract

Since methicillin-resistant Staphylococcus aureus (MRSA) has become one of the most prevalent nosocomial pathogens and a frequent cause of mortality and morbidity, there is an increasing tendency to use topical mupirocin for eradication of MRSA carriage. However, there have been recent reports of resistance against mupirocin among MRSA isolates. This study was conducted to investigate the presence of mupirocin resistance in a population of 595 nosocomial MRSA isolates by phenotypic and genotypic methods. In 35 (5.9%) of 595 isolates, mupirocin resistance was detected by disc diffusion and E-test methods. High-level mupirocin resistance was detected in 23 (65.8%) isolates and low-level mupirocin resistance in 12 (34.2%) isolates by E-test method. The molecular analysis of 35 mupirocin resistant MRSA isolates showed the presence of both mecA and mupA genes by polymerase chain reaction. While in 23 high-level mupirocin resistant MRSA isolates a 38 kb plasmid was detected, none of the low-level mupirocin-resistant MRSA isolates revealed the presence of this plasmid. Thirty-two of 35 mupirocin resistant MRSA isolates were genotyped with pulsed-field gel electrophoresis and 24 isolates were typed as identical (genotype A) and 8 as genetically-related (genotype A1), according to Tenover criteria. These data revealed that mupirocin resistant MRSA isolates in our hospital were of the same genotype or closely related.