Identification of non-PBP2a resistance mechanisms in Staphylococcus aureus after serial passage with ceftaroline: involvement of other PBPs
Identification of non-PBP2a resistance mechanisms in Staphylococcus aureus after serial passage with ceftaroline: involvement of other PBPs
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DOI：
10.1093/jac/dkw282
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发表时间：
2016-11-01
影响因子：
5.2
通讯作者：
Alm, Richard A.
中科院分区：
文献类型：
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作者：
Lahiri, Sushmita D.;Alm, Richard A.
头孢洛林（头孢洛林酯的活性代谢产物）是一种头孢菌素，由于其对PBP 2a的高亲和力，因此具有抗MRSA的活性。已知PBP 2a序列变异，包括转肽酶结合口袋外的一些变异，影响头孢洛林敏感性，最近的证据表明非PBP 2a机制参与头孢洛林耐药性。本研究评价了头孢洛林在连续传代过程中选择耐药金黄色葡萄球菌克隆的潜力。金黄色葡萄球菌分离株（两种MRSA和一种MSSA）在肉汤中随着选择压力的增加而增加。检测出现的突变体的头孢洛林敏感性变化并进行遗传表征。MSSA分离株在PBP 2和PBP 3中发生突变，使头孢洛林MIC增加16倍，并增加其他β-内酰胺类药物的MIC。在一株MRSA分离株中，PBP 2a转肽酶口袋中的Glu（447）Lys取代使头孢洛林MIC升高至8 mg/L。头孢洛林耐药MRSA分离株中的选择性压力产生LytD突变，以及先前显示导致PBP 4过表达的pbp 4启动子的变化，这是一种不受头孢洛林抑制的PBP。当与极低水平的可抑制PBP 4功能的甲氧西林或美罗培南联合试验时，升高的头孢洛林MIC被逆转。这些研究表明，头孢洛林的耐药性可通过多种机制表现出来。此外，他们支持这样的假设，即当PBP 2a被抑制时，PBP 4可以在功能上提供MRSA细胞壁生物发生所需的基本转肽酶活性。
Ceftaroline (the active metabolite of ceftaroline fosamil) is a cephalosporin that possesses activity against MRSA due to its differentiating high affinity for PBP2a. It is known that PBP2a sequence variations, including some outside of the transpeptidase-binding pocket, impact ceftaroline susceptibility and recent evidence suggests involvement of non-PBP2a mechanisms in ceftaroline resistance. This study evaluated the potential of ceftaroline to select for resistant Staphylococcus aureus clones during serial passage.Selection experiments were performed by up to 20 daily passages of three S. aureus isolates (two MRSA and one MSSA) in broth with increasing selective pressure. Mutants that emerged were tested for changes in ceftaroline susceptibility and genetically characterized.The MSSA isolate developed mutations in PBP2 and PBP3 that increased the ceftaroline MIC by 16-fold and increased the MICs of other beta-lactams. A Glu(447)Lys substitution in the PBP2a transpeptidase pocket in one MRSA isolate elevated the ceftaroline MIC to 8 mg/L. Selective pressure in a ceftaroline-resistant MRSA isolate generated mutations in LytD, as well as changes in the pbp4 promoter previously shown to result in PBP4 overexpression, the one PBP not inhibited by ceftaroline. Elevated ceftaroline MIC was reversed when tested in combination with extremely low levels of methicillin or meropenem that could inhibit the function of PBP4.These studies demonstrate that resistance to ceftaroline can be manifested through numerous mechanisms. Further, they support a hypothesis where PBP4 can functionally provide the essential transpeptidase activity required for MRSA cell wall biogenesis when PBP2a is inhibited.