DEVELOPMENT AND EVALUATION OF A PCR-BASED IMMUNOASSAY FOR THE RAPID DETECTION OF METHICILLIN-RESISTANT STAPHYLOCOCCUS-AUREUS

A multiplex polymerase chain reaction (PCR), involving detection of th e mecA and femB genes, was combined with a novel immunoassay system ca pable of detecting specific PCR products. The resulting PCR-immunoassa y was evaluated in comparison with conventional microbiological techni ques used in the routine diagnostic laboratory for the rapid identific ation of methicillin-resistant Staphylococcus aureus (MRSA), either in pure culture or in overnight broth cultures obtained following enrich ment of patient screening swabs. Among the 480 purified isolates of st aphylococci and 246 enrichment broths examined, only one 'false-negati ve' result was obtained by PCR, compared with 18 'false-negative' resu lts obtained by conventional methodology and demonstrated by further c onventional examination. Five demonstrable 'false-positive' results we re obtained by conventional methodology, compared with a possible 10 b y the PCR-immunoassay, although it was not certain that these 10 PCR r esults were true 'false positives' as, by definition, MRSA could not b e isolated by conventional methodology. The results indicated that the routine diagnostic laboratory was encountering difficulties in identi fying MRSA correctly, and that the conventional microbiological techni ques lacked sensitivity. Overall, the PCR technique was more accurate and sensitive than conventional methodology in detecting MRSA, and res ults were available within 24 h of screening swabs arriving in the lab oratory, compared with a minimum of 48-72 h by conventional techniques . The immunoassay system added to the usefulness of the method by allo wing the detection of specific PCR products within 5 min of completing the PCR, without the normal additional step of agarose gel electropho resis.