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KMID : 0384119870070020265
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Korean Journal of Clinical Pathology
1987 Volume.7 No. 2 p.265 ~ p.273
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Prevalence of Methicillin-resistrant Staphylococcus Aureus and Comparison of Susceptibility Test Methods for Its Detection
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Abstract
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Methicillin-resistant Staphylococus aureus(MRSA)is a recently recognized nosoco￢mial pathogen notorious for multiple drug resistance. The commonly used disk diff￢usion antimicrobial susceptibility test is prone to give both false methicillin resis￢tance and susceptibility. In this study the prevalence rates of MRSA in two general hospitals, one ..in Seoul and the other in a semirural city, were compared and the methods of MRSA detection were also compared. Isolates of S. aureus,150 from Severance Hospital, and 132 from Wonju Christian Hospital, which were isolated during August and November, 1986, were tested for their methicillin susceptibilities by the agar dilution, agar screening and disk diffusion tests. The effects of various test conditions on the disk diffusion test were also compared. By the agar dilution test, 23.3% and 25.5% of S. aureus from Severance and Wonju Hospital respectively were methicillin resistant. Among the MRSA 94.3% and 83.0% respectively were from inpatients. Minimum inhibitory concentration (MIC) range of methicillin against the MRSA was 16 to)´128ug /ml, MIC5o 32 or 64ug/mI and MIC9o128 or> 128ug/ml depending on the hospital. MRSA detection by the agar screening test and by the disk diffusion test were 100% and 94. 9% agreement with agar dilution test.
Heteroresistant MRSA was not found among the isolates tested. In the disk diffu￢sion test, the inhibition zone tended to become larger when incubated at 30°C, and smaller when incubated more than 24 hours. More than 83% of MRSA isolates were resistant to chloramphenicol, erythromycin, and tetracycline, and more than 54% to clindamycin. MIC50 of vancomycin was 1 ug/ml whereas those of cefamandole and other cephalosporins were Bug/ml and 32ug/ml respectively. It is concluded that MRSA is quite prevalent
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KEYWORD
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