Kusuma Caroline M, Kokai-Kun John F
Biosynexus Incorporated, 9119 Gaither Rd., Gaithersburg, MD 20877.
Antimicrob Agents Chemother. 2005 Aug;49(8):3256-63. doi: 10.1128/AAC.49.8.3256-3263.2005.
Lysostaphin is an endopeptidase that cleaves the pentaglycine cross-bridges of the staphylococcal cell wall rapidly lysing the bacteria. Recently, lysostaphin has been examined for its potential to treat infections and to clear Staphylococcus aureus nasal colonization, requiring a reliable method for determining the lysostaphin susceptibility of strains of S. aureus. We compared four methods for determining the lysostaphin susceptibility of 57 strains of methicillin-sensitive S. aureus, methicillin-resistant S. aureus, vancomycin intermediately susceptible S. aureus (VISA), mupirocin-resistant S. aureus, and various defined genetic mutants of S. aureus. Three reference lysostaphin-resistant S. aureus variants were also included in the assays as negative controls. The assays examined included turbidity, MIC, minimum bactericidal concentration (MBC), and disk diffusion assays. All of the strains of S. aureus tested, including a VISA strain which had previously been reported to be lysostaphin resistant, were susceptible to lysostaphin by all four methods. The three reference lysostaphin-resistant variants were resistant by all four methods. The disk diffusion assay was the simplest method to differentiate lysostaphin-susceptible S. aureus strains from lysostaphin-resistant variants, while the MBC assay could be used as a follow-up assay if required. In the disk diffusion assay, all strains of S. aureus tested revealed zones of inhibition of >/=11 mm using a 50-microg lysostaphin disk, while the three reference lysostaphin-resistant S. aureus variants had no zones of inhibition. In MBC assays, concentrations of lysostaphin ranging from 0.16 microg/ml to 2.5 microg/ml were found to cause a 3 log or greater drop from the initial CFU of S. aureus within 30 min for all strains tested.
溶葡萄球菌酶是一种内肽酶，可裂解葡萄球菌细胞壁的五肽甘氨酸交联桥，从而迅速裂解细菌。最近，人们对溶葡萄球菌酶治疗感染和清除金黄色葡萄球菌鼻腔定植的潜力进行了研究，这需要一种可靠的方法来确定金黄色葡萄球菌菌株对溶葡萄球菌酶的敏感性。我们比较了四种用于确定57株甲氧西林敏感金黄色葡萄球菌、耐甲氧西林金黄色葡萄球菌、万古霉素中度敏感金黄色葡萄球菌（VISA）、耐莫匹罗星金黄色葡萄球菌以及各种特定基因变异的金黄色葡萄球菌对溶葡萄球菌酶敏感性的方法。三种耐溶葡萄球菌酶的金黄色葡萄球菌参考变体也作为阴性对照纳入了检测。所检测的方法包括比浊法、最低抑菌浓度（MIC）、最低杀菌浓度（MBC）和纸片扩散法。所有测试的金黄色葡萄球菌菌株，包括一株先前报道对溶葡萄球菌酶耐药的VISA菌株，通过所有四种方法检测均对溶葡萄球菌酶敏感。三种耐溶葡萄球菌酶的参考变体通过所有四种方法检测均耐药。纸片扩散法是区分溶葡萄球菌酶敏感金黄色葡萄球菌菌株和耐溶葡萄球菌酶变体的最简单方法，而如果需要，MBC法可作为后续检测方法。在纸片扩散法中，使用50微克溶葡萄球菌酶纸片检测时，所有测试的金黄色葡萄球菌菌株均显示抑菌圈直径≥11毫米，而三种耐溶葡萄球菌酶的金黄色葡萄球菌参考变体没有抑菌圈。在MBC检测中，对于所有测试菌株，发现溶葡萄球菌酶浓度在0.16微克/毫升至2.5微克/毫升范围内，可在30分钟内使金黄色葡萄球菌的初始菌落形成单位（CFU）下降3个对数或更多。
