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KMID : 0981820100300060637
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Korean Journal of Laboratory Medicine
2010 Volume.30 No. 6 p.637 ~ p.646
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Evaluation of the Performance of the MicroScan Pos Breakpoint Combo Panel Type 28 for Susceptibility Testing of Staphylococcus aureus: Low-range Minimum Inhibitory Concentration of Vancomycin, Cefoxitin Screening, and Inducible Clindamycin Resistance Detection
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Ji Mi-Suk
Lee Mi-Young
Noh Sin-Ae
Kim Mi-Na
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Abstract
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Background : Susceptibility testing of Staphylococcus aureus often requires cumbersome supplementary tests. MicroScan Pos Breakpoint Combo Panel Type 28 (PBC28) (Siemens, USA) includes cefoxitin screening to detect methicillin-resistant Staphylococcus aureus (MRSA), inducible clindamycin resistance detection (ICD), and determination of low-range minimum inhibitory concentration of vancomycin (0.5-16 mg/mL). The purpose of this study was to evaluate the performance of PBC28 in comparison with that of Pos Combo Type 1A (PC1A) (Siemens).
Methods : From December 2009 to March 2010, 500 non-duplicate clinical isolates of S. aureus were tested with PC1A and PBC28. Categorical agreements (CA) between the interpretations of the 2 panels were estimated. The presence of the mecA gene was determined by PCR, and double- disk diffusion test (D-test) was performed on the isolates resistant to erythromycin but susceptible or intermediately resistant to clindamycin. Ninety-six isolates representing various vancomycin minimum inhibitory concentrations (MICs) were tested in parallel with repeat PBC28, broth macrodilution, and epsilometer test (E test).
Results : The CA was 99.3% with a very major error (VME) of 0.2%, major error (ME) of 0.1%, and minor error (mE) of 0.4% in total. PBC28 showed 100% CA for 1 isolate with vancomycin MIC of 4 mg/mL and 35 isolates (7.0%) with MIC of 2 mg/mL. However, only 15, 27, and 35 isolates with vancomycin MIC of 2 mg/mL showed 100% CA in repeat PBC28, broth macrodilution, and E test, respectively. PC1A and PBC28 detected all 314 mecA-positive isolates. Among the 63 isolates tested with the D-test, 58 (92.1%) were positive, and the results were 100% concordant with those of ICD.
Conclusions : PBC28 can be appropriate susceptibility testing of S. aureus, including MRSA detection and ICD. However, the lower-range vancomycin MIC test was not reproducible enough to reliably differentiate MIC of 2 mg/mL from MIC≤1 mg/mL.
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KEYWORD
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Staphylococcus aureus, susceptibility test, MRSA, clindamycin resistance, vancomycin resistance
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