Detection of novel chromosome-SCCmec variants in Methicillin Resistant Staphylococcus aureus and their inclusion in PCR based screening

Abstract

Findings: To facilitate automation, a novel DNA extraction method for MRSA was adopted. The MRSA specific chromosome-SCCmec PCR was adapted, additional primers were added, and the performance was validated. From various laboratories in The Netherlands we received a total of 86 MRSA clinical isolates, that were negative in commercially available tests. We identified 14 MRSA strains with new variant chromosome-SCCmec junctions by sequence analysis. These MRSA strains appeared to carry SCCmec sequences with a high degree of homology to SCC regions of S. epidermidis and S. haemolyticus. All were included for detection in chromosome-SCCmec based PCR.

Background: Efficient management of Methicillin Resistant Staphylococcus aureus (MRSA) in the hospital is needed to prevent dissemination. It is important that MRSA can be rapidly identified, and effective infection control measures can be initiated. Equally important is a rapid MRSA negative report, especially for patients in isolation. For negative screening we implemented fully automated high through-put molecular screening for MRSA.

Conclusions: Fourteen variant chromosome-SCCmec junctions in MRSA, that are not detected in commercially available MRSA detection kits were added to our PCR to detect all currently known variant SCC-mec types of MRSA.

Figure 1

Alignment of right SCC-OrfX junctions. Strains are designated by the primers based on their sequences. OrfX starts at bp 55 (according to Ito et al. [10]. SA; S. aureus, SE; S. epidermidis, SH; S. haemolyticus, SR; Staphylococcal repeats. Strains without any homology to known sequences were omitted from the comparison.