Objectives To investigate the genomic diversity and β-lactam susceptibilities of Enterococcus faecalis collected from patients with infective endocarditis (IE). Methods We collected 60 contemporary E. faecalis isolates from definite or probable IE cases identified between 2018 and 2021 at the University of Pittsburgh Medical Center. We used whole-genome sequencing to study bacterial genomic diversity and employed antibiotic checkerboard assays and a one-compartment pharmacokinetic–pharmacodynamic (PK/PD) model to investigate bacterial susceptibility to ampicillin and ceftriaxone both alone and in combination. Results Genetically diverse E. faecalis were collected, however, isolates belonging to two STs, ST6 and ST179, were collected from 21/60 (35%) IE patients. All ST6 isolates encoded a previously described mutation upstream of penicillin-binding protein 4 (pbp4) that is associated with pbp4 overexpression. ST6 isolates had higher ceftriaxone MICs and higher fractional inhibitory concentration index values for ampicillin and ceftriaxone (AC) compared to other isolates, suggesting diminished in vitro AC synergy against this lineage. Introduction of the pbp4 upstream mutation found among ST6 isolates caused increased ceftriaxone resistance in a laboratory E. faecalis isolate. PK/PD testing showed that a representative ST6 isolate exhibited attenuated efficacy of AC combination therapy at humanized antibiotic exposures. Conclusions We find evidence for diminished in vitro AC activity among a subset of E. faecalis IE isolates with increased pbp4 expression. These findings suggest that alternate antibiotic combinations against diverse contemporary E. faecalis IE isolates should be evaluated.

中文翻译：

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粪肠球菌感染性心内膜炎临床分离株对氨苄西林/头孢曲松联合治疗的体外敏感性差异

目的 研究感染性心内膜炎 (IE) 患者粪肠球菌的基因组多样性和 β-内酰胺敏感性。方法 我们从匹兹堡大学医学中心 2018 年至 2021 年间发现的确诊或疑似 IE 病例中收集了 60 株当代粪肠球菌分离株。我们使用全基因组测序来研究细菌基因组多样性，并采用抗生素棋盘分析和单室药代动力学-药效 (PK/PD) 模型来研究细菌对氨苄青霉素和头孢曲松单独使用和联合使用的敏感性。结果 收集了遗传多样性的粪肠球菌，然而，从 21/60 (35%) IE 患者中收集了属于两个 ST（ST6 和 ST179）的分离株。所有 ST6 分离株均编码先前描述的青霉素结合蛋白 4 (pbp4) 上游突变，该突变与 pbp4 过度表达相关。与其他分离株相比，ST6 分离株具有更高的头孢曲松 MIC 和更高的氨苄青霉素和头孢曲松 (AC) 分数抑制浓度指数值，表明体外 AC 对该谱系的协同作用减弱。 ST6 分离株中发现的 pbp4 上游突变的引入导致实验室粪肠球菌分离株中的头孢曲松耐药性增加。 PK/PD 测试表明，代表性 ST6 分离株在人源化抗生素暴露下表现出 AC 联合疗法的功效减弱。结论 我们发现了 pbp4 表达增加的粪肠球菌 IE 分离株亚群中体外 AC 活性降低的证据。这些发现表明，应评估针对多种当代粪肠球菌 IE 分离株的替代抗生素组合。