Evaluation of the MRSA-Screen test in detecting oxacillin resistance in community and hospital isolates of Staphylococcus aureus

• Published in: Pathology Vol. 33; no. 4; pp. 493 - 495
• Main Authors: Gosbell, I.B., Neville, S.A., Mercer, J.L., Fernandes, L.A., Fernandes, C.J.
• Format: Journal Article
• Language: English
• Published: London Elsevier B.V 01-11-2001; Informa UK Ltd; Taylor and Francis
• Subjects: Antibacterial agents; Antibiotics. Antiinfectious agents. Antiparasitic agents; Antibodies, Monoclonal; Biological and medical sciences; Community-Acquired Infections - microbiology; Cross Infection - microbiology; DNA, Bacterial - analysis; Dose-Response Relationship, Drug; Latex Fixation Tests; Latex test; Medical sciences; methicillin (oxacillin) resistance; Methicillin Resistance; Microbial Sensitivity Tests - economics; Microbial Sensitivity Tests - methods; Oxacillin - pharmacology; Penicillins - pharmacology; Pharmacology. Drug treatments; Polymerase Chain Reaction; Predictive Value of Tests; Sensitivity and Specificity; Staphylococcal Infections - microbiology; Staphylococcus aureus; Staphylococcus aureus - classification; Staphylococcus aureus - drug effects; Staphylococcus aureus - genetics; ORSA; OSSA; Latex test; CA-ORSA; methicillin (oxacillin) resistance; MORSA; Staphylococcus aureus; PCR; NORSA; β-Lactams; Exploration; In vitro; Infection; Penicillin derivatives; Polymerase chain reaction; Antibiotic; Oxacillin; Microorganism resistance; Latex agglutination test; Bacteria; Micrococcales; Micrococcaceae; Technique; Antibacterial agent; Molecular biology; Comparative study
• ISSN: 0031-3025; 1465-3931
• DOI: 10.1080/00313020120083214

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 oxa-cillin-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 p-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 60s to react. MORSA strains took a median 12s (range 5–60s) to give a positive reaction with the MRSA-Screen Test, whereas NORSA strains took a median 30s (range 5–180s), a difference which was significantly different (P<0.0001, two-tailed Mann-Whitney unpaired two sample test). NORSA strains had an MIC50 of 128mg/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 3min should be allowed to elapse before calling a test negative. Organisms giving indeterminate reactions should be tested for the mecA gene by PCR.