Eighty-eight RIF-R S. 3-deazaneplanocin A aureus isolates were re-identified by
the disk diffusion method and used for the present study. The RIF-R S. aureus isolates represented 31% of all S. aureus isolates in 2008. The origin of the strains was mainly from respiratory samples and also from blood cultures, catheter-related sites, Urine samples, wound swabs, respiratory samples and exudates. Oral informed consent was given by all patients before taking the clinical specimen. The S. aureus isolates were re-identified by Gram’s staining, microscopic examination, coagulase testing and catalase Bafilomycin A1 manufacturer testing. MRSA was initially screened by the cefoxitin disk diffusion method, and then confirmed by polymerase chain reaction (PCR) detecting mecA.
Antimicrobial susceptibility testing Two hundred and eighty-three S. aureus susceptibility to penicillin (10 units), ampicillin/sulbactam (10/10μg), cefazolin (30μg), vancomycin (30μg), erythromycin (15μg), clindamycin (2μg), rifampicin (5μg), linezolid (30μg), mupirocin (5μg), quinupristin/dalfopristin (15μg), tetracycline (30μg), trimethoprim/sulfamethoxazole find more (1.25/23.75μg), gentamicin (10μg), ciprofloxacin (5μg), and levofloxacin (5μg) were determined by using the disk diffusion method in accordance with standards recommended by the Clinical and Laboratory Standards Institute (CLSI) . Reference strain ATCC25923 was used for quality control. MICs of rifampicin for all S. aureus isolates 4-Aminobutyrate aminotransferase were further determined by the agar dilution method , and S. aureus ATCC 29213 and E.coli ATCC25922 were designated as RIF-S and RIF-R controls, respectively. According to the CLSI criteria , isolates were interpreted
as RIF-S (MIC≤1 mg/L) and RIF-R (MIC≥4 mg/L) isolates. Detection of rifampicin resistance-associated mutations Total DNA from S. aureus was purified and used as a template for amplification by PCR. An internal gene sequence of 432 bp (nucleotides 1216 to 1648), was amplified by PCR. This region included the rifampicin resistance-determining cluster I (nucleotides 1384–1464, amino acid number 462–488) and cluster II (nucleotides 1543–1590, amino acid number 515–530). The amplification was carried out in 88 RIF-R strains. Amplification was carried out as previously described . The PCR products were purified and analyzed by DNA sequencing. The nucleotide sequences obtained were compared to the rpoB wild type sequence from S.aureus subsp. aureus (GenBank accession number: X64172) using the clustalw software(http://www.ebi.ac.uk/tools/clustalw/index.html). Molecular typing SCCmec typing SCCmec typing of MRSA isolates was performed using eight unique and specific pairs of primers for SCCmec types and subtypes I, II, III, IV and V as described previously .