Detection of borderline oxacillin-resistant Staphylococcus aureus and differentiation from methicillin-resistant strains.
Detection of borderline oxacillin-resistant Staphylococcus aureus and differentiation from methicillin-resistant strains.
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边缘耐苯唑西林金黄色葡萄球菌的检测以及与耐甲氧西林菌株的区分。
DOI：
10.1007/bf02184683
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发表时间：
1990
期刊：
影响因子：
--
通讯作者：
Jungkind,D
中科院分区：
文献类型：
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作者：
Liu,H;Buescher,G;Lewis,N;Snyder,S;Jungkind,D
对88株符合苯唑西林临界耐药标准的金黄色葡萄球菌(苯唑西林中度敏感或耐药，纸片扩散法对阿莫西林/克拉维酸敏感)进行研究，以确定鉴别耐苯唑西林金黄色葡萄球菌(Borsa)和耐甲氧西林金黄色葡萄球菌(MRSA)的最佳试验方法和条件。进一步检测发现了三种不同的耐药模式：61株(69%)始终符合Borsa标准，平均β-内酰胺酶水平比苯唑西林敏感对照高5-6倍；11株(13%)MRSA明显异质性耐药，耐药菌落出现延迟，导致对阿莫西林/克拉维酸的假性敏感性；16株(18%)重复试验显示对苯唑西林敏感。在用于诱导金黄色葡萄球菌对甲氧西林产生内在耐药性的条件下，很大比例的Borsa对阿莫西林/克拉维酸表现出耐药。这清楚地表明，Borsa可能被误认为MRSA，而异耐药的MRSA可能似乎是Borsa。结论：阿莫西林/克拉维酸区带大小应在培养24小时后测量，金黄色葡萄球菌在特定环境条件下的药敏试验应慎重解释，MIC试验是区分金黄色葡萄球菌这两种耐药模式的最可靠方法。
Eighty-eightStaphylococcus aureusclinical isolates meeting criteria for borderline oxacillin resistance (intermediate susceptibility or resistance to oxacillin but susceptibility to amoxicillin/clavulanic acid upon disk diffusion testing) were studied to determine optimal test techniques and conditions for differentiating borderline oxacillin-resistantStaphylococcus aureus(BORSA) from methicillin-resistantStaphylococcus aureus(MRSA). Further testing revealed three distinct resistance patterns: 61 strains (69 %) consistently met BORSA criteria and had average beta-lactamase levels five- to six-fold higher than oxacillin-susceptible controls; 11 strains (13 %) were markedly heteroresistant MRSA with delayed appearance of resistant colonies leading to spurious susceptibility to amoxicillin/clavulanic acid; 16 strains (18 %) appeared to be oxacillin-susceptible on repetitive testing. Under conditions used to elicit intrinsic methicillin resistance inStaphylococcus aureus, a large percentage of BORSA appeared resistant to amoxicillin/clavulanic acid. This clearly shows that BORSA may be misidentified as MRSA while heteroresistant MRSA may appear to be BORSA. It is concluded that amoxicillin/clavulanic acid zone sizes should be measured after a full 24 hours of incubation, that susceptibility testing ofStaphylococcus aureusunder certain environmental conditions should be interpreted with caution, and that MIC testing is the most reliable technique for differentiating these two resistance patterns inStaphylococcus aureus.