Multiplex PCR Strategy for Rapid Identification of Structural Types and Variants of the <i>mec</i> Element in Methicillin-Resistant <i>Staphylococcus aureus</i>

TLDR

MRSA characterization requires knowledge of both bacterial genetics and the complex mec element structure linked to mecA-mediated resistance. The study develops, validates, and applies a multiplex PCR strategy for rapid presumptive characterization of mec element types in MRSA. The strategy was validated on a representative set of pandemic MRSA clones with known mec element structures and then tested alongside multilocus sequence typing on 18 outbreak isolates from Barcelona. The assay rapidly and robustly identified five mec element structural types—three major and two minor variants—among the isolates, demonstrating its utility as a molecular typing tool for MRSA clonal characterization.

Abstract

ABSTRACT Full characterization of methicillin-resistant Staphylococcus aureus (MRSA) requires definition of not only the bacterial genetic background but also the structure of the complex and heterologous mec element these bacteria carry, which is associated with drug resistance determinant mecA . We report the development, validation, and application of a multiplex PCR strategy that allows quick presumptive characterization of the mec element types based on the structural features that were shown to be typical of mec elements carried by several MRSA clones. The strategy was validated by using a representative collection of pandemic MRSA clones in which the full structure of the associated mec elements was previously determined by hybridization and PCR screenings and also by DNA sequencing. The method was tested together with multilocus sequence typing and other typing methods for the characterization of 18 isolates representative of the MRSA clones recovered during a hospital outbreak in Barcelona, Spain. The multiplex PCR was shown to be rapid, robust, and capable in a single assay of identifying five structural types of the mec element among these strains, three major and two minor variants, each one of which has been already been seen among MRSA characterized earlier. This technique should be a useful addition to the armamentarium of molecular typing tools for the characterization of MRSA clonal types and for the rapid tentative identification of structural variants of the mec element.