DOI: 10.14457/tu.the.2017.1314
title: Molecular characterization of methicillin-resistant Staphylococcus aureus (MRSA) and factors associated with clinical outcomes in MRSA-infected patients at Thammasat University Hospital

description: Methicillin-resistant Staphylococcus aureus (MRSA) is one of the most common nosocomial pathogens. Clinical outcomes by this pathogen ranges from skin and soft tissue infection, musculoskeleton infection, respiratory tract infection, and bloodstream infection. Treatment failure of MRSA infections have been increasingly common, leading to rising numbers of mortality and morbidity cases. Factors, either clinical factors or microbiological factors, which may be responsible for the treatment failure have not been investigated in Thammasat University Hospital. The aim of this study was to find the factors contributing to the outcomes of treatment with vancomycin in the patients infected by MRSA.  MRSA strains were characterized by using several methods including broth micro-dilution method, E-test method, Population Analysis Profile (PAP), Polymerase chain reaction (PCR) technique, SCCmec typing and Pulsed field gel electrophoresis (PFGE). Regression analysis method was used to analyze the association of clinical and microbiological factors with the treatment outcomes.  A total 101 MRSA isolates were collected at Thammasat University Hospital during August 2012 to July 2015. Although vancomycin, teicoplanin and linezolid, still remained as effective antibiotics for treatment of all MRSA infections, it was found that the vancomycin MICs creep rate was 31%. There were no significant differences in terms of clinical failure rate between patients with MRSA isolates with vancomycin MICs creep or non-creep. By using univariate regression analysis, heterogeneous vancomycin intermediate S. aureus (hVISA) strains were found to be significantly associated with the treatment failure in patients with MRSA infections (p =0.03). The multivariate regression analysis indicated that chronic hemodialysis (OR=5.77; 95% CI: 1.7-19.49; p = 0.00), multiple sites infection (OR=3.71; 95% CI: 1.08-12.77; p =0.03), co-microbe resistant strains (OR=3.68; 95% CI: 1.16-11.65; p =0.02) were significant factors associated with clinical failure in MRSA-infected patients. All MRSA isolates were positive for mecA, femA and icaA genes, whereas all isolates were negative for sec, sed, eta, etb, tst, and pvl genes. Furthermore, sea, seb, and see genes were found in 43%, 38% and 43% of all isolates. Six different virulence genes patterns designated type I (40%), II (37%), III (19%), IV (2%), V (2%) and VI (1%) were exhibited. The isolates were classified as SCCmec type I (36%), type II (41%) and type III (24%). PFGE differentiated all MRSA isolates into 17 patterns, designated as types A-Q. The majority of isolates were type A (16%). There were no significant associations between the specific virulence gene pattern, SCCmec-type, PFGE pattern and clinical outcomes. In conclusion, the findings of this study showed the factors that were associated with the treatment failure among patients infected with MRSA. Along with providing standard medical treatment, closely monitoring and controlling these factors may improve the overall outcomes of patients suffered from the MRSA infections.