The primary mechanism of fusidic acid resistance in S. aureus relates to mutations in fusA, the gene that encodes the ribosomal translocase and translation elongation Raf inhibitor factor EF-G [12, 13]. More than 30 different amino acid substitution mutations in fusA have been identified [12, 14, 15]. Subsequently, resistance in natural isolates may also result from the horizontal acquisition of fusB, a poorly
characterized plasmid-mediated resistance mechanism . The gene fusB is usually carried by a 21-kb plasmid, pUB101 , however, it can also be chromosomal . The fusB gene encodes an inducible protein that protects an in vitro translation system against the inhibitory action of fusidic acid . Recently, two fusB homologues, designated fusC and fusD, have been identified in the chromosome of clinical isolates of S. aureus and S. saprophyticus, respectively . In addition, fusidic acid-resistant small-colony variants (SCVs) of S. aureus with mutations in rplF have been designated as FusE mutants . Although frequencies of resistance to fusidic acid have remained generally low, each of these mechanisms has multiple genetic causes, and
emerging resistance is a problem that could limit the therapeutic options available for treatment of staphylococcal infections . In this study, a series of MRSA clinical isolates recovered at a regional teaching hospital in middle Taiwan showing fusidic acid MIC ≥ 2 μg/ml. The high distribution selleck chemicals llc of fusidic acid resistance determinants fusC was confirmed in MRSA. In addition, different fusidic acid resistance determinants-containing in one isolate was also demonstrated. Methods Bacterial isolates From April 2007 to January 2008, 34 clinical isolates of MRSA with fusidic acid resistance were recovered from 34 different patients Thymidylate synthase at Tungs’ Taichung MetroHarbor Hospital (TTMHH), a 1405-bed regional teaching hospital in central Taiwan. S. aureus ATCC 29213 and NCTC 8325 have consistently been used as a quality control strain and Pulsed Field Gel Electrophoresis (PFGE) standard strain, respectively. Luria-Bertani (LB) agar and LB broth were used for bacterial growth
at 37°C with aeration. Mueller-Hinton agar was used for all determinations of minimum inhibitory concentrations (MICs). All isolates were identified on the colony morphology, Gram’s stain, a positive catalase reaction and/or results obtained with the phoenix system (BD Diagnostic Systems, Sparks, MD, USA) and frozen at -80°C until used. Antimicrobial susceptibility tests MICs of different antimicrobial agents were determined using the Phoenix Automated Microbiology System (BD Diagnostic Systems, Sparks, MD) and interpreted according to the criteria provided by the Clinical and Laboratory Standards Institute (CLSI). Fusidic acid susceptibility was screened by the disk diffusion method with 10 μg fusidic acid containing disks. The interpretive criterion of susceptibility was an inhibition zone ≥ 22 mm in diameter.