Test code links throughout this Guide refer to the corresponding test in the User's Guide. A gene that encodes for methicillin resistance among coagulase negative and coagulase positive staphylococci. Two-thirds of all clinical isolates are resistant to methicillin. A gene is often heterogeneous, meaning that only a small percentage of bacteria in a culture may exhibit resistance.
Resistant cells grow more slowly than susceptible ones.
Despite recommendations by the National Committee for Clinical Laboratory Standards with respect to specialized growth conditions, clinical microbiology laboratories may have difficulty determining methicillin resistance. ARUP offers a PCR test that amplifies a segment of the mec A gene. This PCR assay is performed directly on all positive blood cultures and is the initial test performed on staphylococcal isolates from significant sources, such as catheter tips, cerebrospinal fluid, joint fluids, and other sterile body sites. This assay can also be used to resolve borderline resistant phenotypes on clinically significant isolates sent by clients. Numerous reports for the detection of MRSA by PCR indicate high sensitivity and rapid turnaround time.