Abstract：
Borderline oxacillin-resistant Staphylococcus aureus (BORSA) are mecA-negative strains with oxacillin minimum inhibitor concentration (MIC) close to the resistance breakpoint of ≥ 4μg/mL. Instead of producing penicillin-binding protein with low affinity to methicillin (oxacillin) mediated by mecA gene as in methicillin-resistant S. aureus (MRSA), BORSA strains are characterised by the hyperproduction of β-lactamase enzymes, thus able to break down methicillin. Common laboratory methods to detect MRSA such as cefoxitin disk diffusion alone may fail to detect methicillin resistance due to BORSA. We report five cases of BORSA blood-stream infections in a university teaching hospital. All isolates were found to be susceptible to cefoxitin using disk diffusion, resistant to oxacillin using automated MIC method, and did not harbour mecA gene. All patients were suscessfully treated with anti-MRSA antibiotics, and removal of primary sources were done if identified. A more cost-effective method for screening and diagnosis of BORSA is needed in addition to cefoxitin disk diffusion test, in order to monitor the spread, and to enable routine detection and treatment of this pathogen.
摘要：
对苯唑西林耐药的金黄色葡萄球菌(BORSA)为mecA阴性菌株,苯唑西林最低抑制剂浓度(MIC)接近耐药断点≥4μg/mL。而不是像耐甲氧西林金黄色葡萄球菌（MRSA）那样产生对mecA基因介导的甲氧西林（苯唑西林）低亲和力的青霉素结合蛋白，BORSA菌株的特征是β-内酰胺酶的过度产生，从而能够分解甲氧西林。检测MRSA的常见实验室方法，例如单独使用头孢西丁纸片扩散可能无法检测到BORSA引起的甲氧西林耐药性。我们报告了一所大学教学医院的5例BORSA血流感染病例。使用圆盘扩散发现所有分离株对头孢西丁敏感，使用自动MIC方法对苯唑西林耐药，也没有携带mecA基因.所有患者均接受抗MRSA抗生素复苏治疗,并清除主要来源，如果确定。除了头孢西丁纸片扩散试验外，还需要一种更具成本效益的方法来筛查和诊断BORSA，为了监测传播，并能够对这种病原体进行常规检测和治疗。
