OBJECTIVES Until recently, the European Committee on Antimicrobial Susceptibility Testing (EUCAST) recommended the cefoxitin disc to screen for mecA-mediated β-lactam resistance in Staphylococcus pseudintermedius. A recent study indicated that cefoxitin was inferior to oxacillin in this respect. We have re-evaluated cefoxitin and oxacillin discs for screening for methicillin resistance in S. pseudintermedius. METHODS We included 224 animal and human S. pseudintermedius isolates from Europe (n = 108) and North America (n = 116), of which 109 were mecA-positive. Disc diffusion was performed per EUCAST recommendations using 30-μg cefoxitin and 1-μg oxacillin discs from three manufacturers and Mueller-Hinton agar from two manufacturers. RESULTS Cefoxitin inhibition zones ranged from 6 to 33 mm for mecA-positive S. pseudintermedius (MRSP) and from 29 to 41 mm for mecA-negative S. pseudintermedius (MSSP). The corresponding oxacillin zone intervals were 6-20 mm and 19-30 mm. For cefoxitin 16% (95% CI 14.8-18.0%) of the isolates were in the area where positive and negative results overlapped. For oxacillin the corresponding number was 2% (1.6-2.9%). For oxacillin a breakpoint of susceptible (S) ≥ 20 mm and resistant (R) <20 mm resulted in only 0.4% and 1.1% very major error and major error rates respectively. CONCLUSIONS This investigation confirms that the 1-μg oxacillin disc predicts mecA-mediated methicillin resistance in S. pseudintermedius better than the 30-μg cefoxitin disc. For a 1-μg oxacillin disc we propose that 20 mm should be used as cut off for resistance, i.e. isolates with a zone diameter <20 mm are resistant to all β-lactam antibiotics except those with activity against methicillin-resistant staphylococci.

中文翻译：

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用于检测伪葡萄球菌中mecA介导的β-内酰胺耐药性的EUCAST光盘扩散标准：奥沙西林vs头孢西丁。

目的直到最近，欧洲抗菌药物敏感性试验委员会（EUCAST）仍建议使用头孢西丁圆片筛查假性葡萄球菌中mecA介导的β-内酰胺耐药性。最近的一项研究表明，头孢西丁在这方面不如奥沙西林。我们已经重新评估了头孢西丁和奥沙西林圆片，以筛选假单胞菌中甲氧西林的耐药性。方法我们纳入了来自欧洲（108例）和北美（116例）的224种动物和人假单胞菌的分离株，其中109株为mecA阳性。根据EUCAST的建议使用30 µg头孢西丁和1 µg oxacillin光盘（来自三个制造商）和Mueller-Hinton琼脂光盘（来自两个制造商）进行光盘扩散。结果mecA阳性S的头孢西丁抑制范围为6到33 mm。pseudintermedius（MRSP），对于mecA阴性的S. pseudintermedius（MSSP）为29到41 mm。相应的奥沙西林区域间隔为6-20 mm和19-30 mm。对于头孢西丁，有16％（95％CI 14.8-18.0％）的分离株位于阳性和阴性结果重叠的区域。对于奥沙西林，相应的数字是2％（1.6-2.9％）。对于奥沙西林，敏感点（S）≥20 mm且断裂点（R）<20 mm的断点分别仅导致非常严重的错误和严重错误率分别为0.4％和1.1％。结论这项研究证实1-μg的奥沙西林片预测假丝酵母中mecA介导的甲氧西林耐药性优于30μg的头孢西丁片。对于1μg的奥沙西林片，我们建议将20 mm用作抗药性的截止点，即区带直径<