Abstract
Methicillin-resistant Staphylococcus aureus (MRSA) infections are prevalent in burn wards, and are especially serious in S. aureus bacteremia (SAB) patients. Glycopeptides and daptomycin are effective against MRSA infections, but MIC creeps can reduce their efficacy. Our object was to perform a molecular epidemiological investigation of S. aureus isolates in our burn center and to evaluate MICs for antimicrobials against SAB-associated MRSA isolates. A total of 259 S. aureus isolates, obtained from August 2011 to July 2016, were used in this study. Multiple molecular typing was used for molecular epidemiological analysis. E-tests were used to determine MICs of vancomycin, teicoplanin, and daptomycin for SAB-associated MRSA isolates. MIC values were stratified by collection date or source and compared. Spearman's test was used to analyze MICs correlations amongst tested antimicrobials. ST239-MRSA-III-t030-agrI clone was found to be dominant in both SAB and non-SAB patients, and significantly more in SAB patients (P < 0.0001). SAB-MRSA isolates exhibited decreased MICs for vancomycin, teicoplanin, and daptomycin during the 5-year period. Compared to those isolated from catheters or wounds, SAB-MRSA isolates from the bloodstream were less susceptible to vancomycin and daptomycin, but more susceptible to teicoplanin. MICs Correlation was found only between vancomycin and daptomycin in MRSA isolates from the bloodstream (rho = 0.250, P = 0.024). In conclusion, our results suggest that MRSA infections are still serious problems in burn centers. In contrast to most other studies, we observed increased susceptibility to glycopeptides and daptomycin against SAB-associated MRSA in our center from 2011 to 2016, suggesting the use of glycopeptides does not lead to MIC creeps. Isolates from different sites of the body may exhibit different levels of susceptibility and change trend over time for different antimicrobials, antimicrobials selection for MRSA infections should be considered comprehensively.
Highlights
Staphylococcus aureus is an important human pathogen that causes infections at diverse sites in the body (Rasigade and Vandenesch, 2014), it is the most frequently isolated Grampositive bacterial species from burn patients (Song et al, 2001; Bayram et al, 2013)
Since our result suggested that S. aureus bacteremia (SAB) patients presented significantly more ST239-Methicillin-resistant Staphylococcus aureus (MRSA)-III-t030-agrI infections, we determined minimum inhibitory concentration (MIC) for all the MRSA isolates from SAB patients using E-tests, and evaluated antimicrobial MICs of these isolates according to their collection dates and sources
For isolates from wounds, the most common isolation site for S. aureus in burn wards, SAB patients were more likely to be infected by the ST239-MRSA-t030 clone compared to non-SAB patients
Summary
Staphylococcus aureus is an important human pathogen that causes infections at diverse sites in the body (Rasigade and Vandenesch, 2014), it is the most frequently isolated Grampositive bacterial species from burn patients (Song et al, 2001; Bayram et al, 2013). The concern is even greater in patients suffering burn-associated infections, since the isolation rate for MRSA in burn wards is much higher than in the general hospital population and the resistance to antimicrobials is more dangerous (Bahemia et al, 2015; Motallebi et al, 2016). In China, ST239MRSA-III-t030-agrI is the most prevalent and persistent MRSA clone, and is a major challenge to clinical anti-infection therapy (Cheng et al, 2013; Li et al, 2013). The ST239 clone may have adaptations that confer enhanced antimicrobial resistance (Cha et al, 2005; Chen et al, 2014), and ST239-MRSA is more likely to be classified as a heterogeneous vancomycin-intermediate S. aureus (hVISA) (Hu et al, 2015)
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