Clinical significance and staphylococcal cassette chromosome mec (SCCmec) characterization of coagulase-negative staphylococci isolated from blood cultures

Abstract

To describe the true coagulase-negative staphylococci (CoNS) bacteremia rate compared with contaminants, and to determine the SCCmec types in methicillin-resistant staphylococci and evaluate the diversity between methicillin-resistant CoNS (MRCoNS) and methicillin-resistant Staphylococcus aureus (MRSA) isolates during a 10-month study period. Materials and methods: The true CoNS bacteremia or bloodstream infection episode was defined on the basis of previous studies on CoNS bacteremia and the definitions of the Centers for Disease Control and Prevention. SCCmec types were determined by using the real-time PCR method. A total of 357 staphylococci isolates, including 313 CoNS and 44 S. aureus, were obtained from 462 positive blood culture samples. Results: A total of 249 CoNS bacteremia episodes in 231 patients were evaluated. Of these episodes, 45 (18.1%) in 41 patients were considered to be true CoNS bacteremia, whereas 204 in 190 patients were found to be contaminant. In the present study, all of the MRSA isolates harbored only SCCmec type III, but MRCoNS strains harbored different SCCmec types and SCCmec type IV was the most prevalent. Conclusion: The true CoNS bacteremia rate was consistently within the range reported in the literature. We also concluded that MRCoNS isolates carrying mostly SCCmec type IV elements may not be related to the presence of MRSA isolates carrying only SCCmec type III element in our institution.