Molecular Markers of Antimicrobial Resistance in Methicillin-Resistant <i>Staphylococcus aureus</i> SCC <i>mec</i> IV Presenting Different Genetic Backgrounds

Abstract

Methicillin-resistant Staphylococcus aureus (MRSA) carrying SCC mec type IV has emerged in hospitals worldwide. The aim of this study was to evaluate phenotypic and molecular characteristics of antimicrobial resistance in MRSA SCC mec IV isolates, presenting different genetic backgrounds, isolated from hospitals in Rio de Janeiro. The antimicrobial resistance of 128 S. aureus type IV isolates from 11 hospitals was characterized by the disk diffusion test and minimum inhibitory concentration (MIC) test. Mutations in par C gene, which encodes ciprofloxacin resistance, and genes associated with macrolide–lincosamide–streptogramin B (MLS b ) resistance were also investigated. MRSA isolates belonging to USA400/ST1 (60 isolates), USA800/ST5 (40), USA1100/ST30 (13), and other 11 (15) lineages were mainly resistant to erythromycin (68%), ciprofloxacin (56%), and clindamycin (50%). The highest antimicrobial resistance rates were found among USA400 isolates ( p &lt; 0.05). The majority of them (90%) carried only the erm (C) gene and mainly presented two mutation types in the par C gene. The msr (A) gene was most frequently found among USA800 isolates ( p &lt; 0.05). Among MRSA type IV isolates from Rio de Janeiro hospitals, multiresistance, including mutations in par C gene, was associated to the USA400/ST1, while the msr (A) gene was associated with USA800/ST5 isolates, highlighting that these lineages could have more potential to persist in a hospital environment.