Abstract
BackgroundThe prevalence of resistance to fusidic acid of methicillin-resistant Staphylococcus aureus (MRSA) was increased each year in a Taiwan hospital. Thirty-four MRSA clinical isolates collected in 2007 and 2008 with reduced susceptibility to FA were selected for further evaluation the presence of resistance determinants.ResultsThe most common resistance determinant was fusC, found in 25 of the 34 MRSA isolates. One of the 25 fusidic acid-resistant MRSA harboured both fusB and fusC, which is the first time this has been identified. Mutations in fusA were found in 10 strains, a total of 3 amino-acid substitutions in EF-G (fusA gene) were detected. Two substitutions with G556S and R659L were identified for the first time. Low-level resistance to fusidic acid (MICs, ≤ 32 μg/ml) was found in most our collection. All collected isolates carried type III SCCmec elements. MLST showed the isolates were MRSA ST239. PFGE revealed nine different pulsotypes in one cluster.ConclusionsOur results indicate that the increase in the number of fusidic acid resistant among the MRSA isolates in this hospital is due mainly to the distribution of fusC determinants. Moreover, more than one fusidic acid-resistance mechanism was first detected in a same stain in our collection.
Highlights
The prevalence of resistance to fusidic acid of methicillin-resistant Staphylococcus aureus (MRSA) was increased each year in a Taiwan hospital
Fusidic acid minimum inhibitory concentrations (MICs) were further determined by an agar dilution method following the Clinical and Laboratory Standards Institute (CLSI) guidelines, and susceptibility was categorized using the European Committee for Antimicrobial Susceptibility Testing (EUCAST)/British Society of Antimicrobial Chemotherapy (BSAC) criteria
Isolates and susceptibility tests The sources of the 34 fusidic acid-resistant MRSA isolates included sputum (n = 9), pus (n = 16), blood (n = 5), urine (n = 2), ascites (n = 1), and tip of a central venous catheter (n = 1) (Table 1)
Summary
The prevalence of resistance to fusidic acid of methicillin-resistant Staphylococcus aureus (MRSA) was increased each year in a Taiwan hospital. The frequently-encountered multi-antibiotic resistance of MRSA has become a major health problem [1,2]. The prevalence of MRSA isolates, most of which are health care associated, has slowly increased since 1982, and the appearance and increasing incidence of communityassociated MRSA infections has been documented. Methicillin resistance among nosocomial S. aureus isolates is common [3,4]. Fusidic acid has been used to treat infections with S. aureus for over 35 years. It is usually used in combination with agents such as vancomycin or rifampin in the treatment of systemic infections caused by MRSA [5]. Fusidic acid inhibits protein synthesis by blocking the elongation of the nascent polypeptide chain through binding to EFG on the ribosome and preventing the dissociation of EF-
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