Evaluation of the MRSA-Screen Test in detecting oxacillin resistance in community and hospital isolates of Staphylococcus aureus.
The MRSA-Screen Test (Denka Seiken Co., Japan), a latex agglutination test to detect penicillin-binding protein 2a, was compared with PCR for the detection of oxacillin resistance in Staphylococcus aureus. A total of 77 oxacillin-sensitive and 269 oxacillin-resistant (ORSA) isolates were evaluated. Of the ORSA isolates, 186 were non-multiresistant (NORSA), defined as being resistant to two or fewer antibiotics other than beta-lactams. Eighty-three were multiresistant ORSA (MORSA) strains. If PCR is considered the gold standard test, then the sensitivity, specificity, positive and negative predictive values of the MRSA-Screen Test were 100, 99, 99 and 100%, respectively. The endpoint was hard to read with NORSA strains that took longer than 60 s to react. MORSA strains took a median 12 s (range 5-60 s) to give a positive reaction with the MRSA-Screen Test, whereas NORSA strains took a median 30 s (range 5-180 s), a difference which was significantly different (P < 0.0001, two-tailed Mann-Whitney unpaired two sample test). NORSA strains had an MIC50 of 128 mg/l and MIC90 of 256mg/l, whereas MORSA strains had an MIC50 and MIC90 of >256mg/l. The time that the MRSA-Screen Test took to agglutinate with ORSA strains correlated weakly with the MIC (r2 = 0.26). Detection of methicillin resistance cost AUD$9 per isolate with the MRSA-Screen Test, compared with AUD$13 per isolate with mecA PCR. The MRSA-Screen Test gave excellent sensitivity and specificity, and was quicker and cheaper than PCR. The full 3 min should be allowed to elapse before calling a test negative. Organisms giving indeterminate reactions should be tested for the mecA gene by PCR.
Gosbell
I B
IB
Department of Microbiology and Infectious Diseases, South Western Area Pathology Service, Liverpool, Australia. i.gosbell@unsw.edu.au
Neville
S A
SA
Mercer
J L
JL
Fernandes
L A
LA
Fernandes
C J
CJ
D000911:Antibodies, Monoclonal; D017714:Community-Acquired Infections / Q000382:microbiology*; D003428:Cross Infection / Q000382:microbiology*; D004269:DNA, Bacterial / Q000032:analysis; D004305:Dose-Response Relationship, Drug; D007841:Latex Fixation Tests; D016106:Methicillin Resistance; D008826:Microbial Sensitivity Tests / Q000191:economics / Q000379:methods; D010068:Oxacillin / Q000494:pharmacology*; D010406:Penicillins / Q000494:pharmacology*; D016133:Polymerase Chain Reaction; D011237:Predictive Value of Tests; D012680:Sensitivity and Specificity; D013203:Staphylococcal Infections / Q000382:microbiology; D013211:Staphylococcus aureus / Q000145:classification / Q000187:drug effects* / Q000235:genetics
D000911:Antibodies, Monoclonal; D004269:DNA, Bacterial; D010406:Penicillins; D010068:Oxacillin