Pulsed-field gel electrophoresis (PFGE) was carried out for all S. aureus isolates, after digesting genomic DNA with SmaI (New England Biolabs, Inc.; Beverly, MA, USA) by the method described previously [24] with pulse times increasing from 1 to 35 seconds and a running time of 23 hours. The Dice index and the un-weighted pair group method with arithmetic average (UPGMA) with 0.5% optimization and 1% position tolerance were used for similarity and cluster analysis. After PFGE, isolates were grouped in genotypes according to their similarities in band patterns [25] and the clonality was obtained by comparisons with previously published pictures [26]. Multilocus sequence typing (MLST) [27] was performed for one representative isolate of each genotype to determine the sequence type (ST). Internal fragments of seven housekeeping genes have been amplified (arcC, encoding carbamate kinase; aroE, shikimate dehydrogenase; glpF, glycerol kinase; gmk, guanylate kinase; pta, phosphate acetyltransferase; tpi, triosephosphate isomerase; and yqiL, acetyl coenzyme A). The allele sequences were analyzed using Bioedit 7.0 software and the MLST database (www.pubmlst.gov). In this technique, each allelle sequence is assigned with a number. The sequence type (ST) (or allelic profile) is based on the combination of the seven assigned numbers [28]. Minimum spanning trees (MST) were created by goeBURST implemented in PHYLOViZ [29] 2.0 software. The STs were represented by circles; the size of a circle is proportional to the number of isolates of this particular ST.

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