Rapid Test for Methicillin Resistance in Staphylococci

A rapid latex test detects penicillin-binding protein 2 (PBP2) as an aid to identifying methicillin-resistant Staphylococcus aureus (MRSA) and methicillin-resistant coagulase-negative staphylococci (MRCoNS).

Penicillin-resistant penicillins (PRPs), such as methicillin and oxacillin, are the drugs of choice to treat staphylococcal infections. Penicillin-binding protein (PBP2), encoded by the MecA gene, is the protein that renders these agents ineffective. A new PBP2 test developed by Oxoid (Basingstoke, UK) has been approved by the U.S. Food and Drug Administration (FDA) for use in the confirmation of resistance in both Staphylococcus aureus and coagulase negative staphylococci. Confirming the presence of PBP2 by latex agglutination is an accurate and reliable method for detecting oxacillin/methicillin resistance and demonstrates 100% accuracy compared to a polymerase chain reaction (PCR).

Latex particles are sensitized with monoclonal antibody against PBP2. When methicillin-resistant staphylococci are tested, the latex particles bind to the extracted PBP2 to cause agglutination. In the absence of PBP2 the latex particles remain in smooth suspension. The test is easier to perform and much quicker than genotypic tests, yielding clearly visible results in just a few minutes.

Vancomycin is used to treat MRSA and MRCoNS but it is more toxic and costly than PRPs, and its overuse could contribute to the selection of vancomycin-resistant organisms. Therefore, rapid and reliable identification of MRSAs are important for prompt initiation of appropriate therapy.



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