Evaluation of the BBL Crystal MRSA ID System for detection of oxacillin resistance in Staphylococcus aureus

Aims - To evaluate the BBL(R) Crystal(TM) MRSA ID System for detection of o xacillin resistance in Staphylococcus aureus. Methods - 52 methicillin resistant S aureus (MRSA) from five different coun tries and 85 methicillin susceptible S aureus (MSSA) were included. The spe cies was confirmed by tube coagulation and detection of the clumping factor using the Staphaurex Plus. Clonal non-identity of the MRSA isolates was sh own by pulsed field gel electrophoresis. MIC values (oxacillin) were determ ined using the Etest. Polymerase chain reaction was carried out to detect t he mecA gene. The BBL Crystal MRSA ID System was carried out according to t he manufacturer's instructions. Results - The BBL Crystal MRSA ID System showed fluorescence in 15 of 52 MR SA (sensitivity 86.5%; negative predicitive value 92.2%), and the specifici ty was 97.6% (positive predicitive value 95.7%). Two of seven MRSA that fai led to show fluorescence had MIC values (oxacillin) of 4 mg/litre. Conclusions - The BBL Crystal MRSA ID System is a valuable test for detecti ng oxacillin resistance in S aureus Its major advantage is the short time ( 4-5 hours) required to perform the test when organisms are grown on tryptic soy agar or sheep blood agar. Difficulties may arise in borderline resista nt isolates.