Identification of methicillin-resistant Staphylococcus aureus (MRSA): Comparison of a new molecular genetic test kit (GenoType MRSA) with standard diagnostic methods.

Results obtained from 188 isolates of staphylococci using standard diagnostic methods for identifying MRSA were compared with those achieved with a newly available molecular genetic test kit, the GenoType, Version 1, MRSA (Hain Lifescience GmbH, Nehren, Germany). The GenoType MRSA detects the mecA gene and, in addition, a highly specific sequence for Staphylococcus aureus (S. aureus) by polymerase chain reaction (PCR) and reverse hybridization. There was a 100% overall correlation between the results of conventional and molecular genetic testing. 143 isolates were tested positive for MRSA, 10 isolates were identified as oxacillin-sensitive Staphylococcus aureus strains (MSSA), and 35 isolates were coagulase-negative staphylococci of various species. However, five of the 143 MRSA strains yielded ambiguous results with the first line standard tests and therefore required additional testing leading to delay of definitive diagnosis. As expected, mecA could not only be detected in MRSA strains, but also in coagulase-negative staphylococci. The reliable identification as S. aureus from the same isolate is therefore an essential prerequisite for MRSA diagnosis. The GenoType MRSA fulfills this requirement by parallel detection of a S. aureus-specific sequence and the mecA gene. Molecular genetic testing with the GenoType MRSA kit needs much less time than conventional microbiological methods. Therefore genetic testing provides not only a considerable advantage with respect to reliability but also to speed.