The Enterobacter cloacae complex (ECC) is one of the most common causes of bacteremia and leads to poor clinical outcomes. The aim of this study was to clarify the antimicrobial susceptibility profiles and genetic backgrounds of non-carbapenemase-producing reduced-carbapenem-susceptible (RCS) ECC blood isolates in Japan using agar dilution antimicrobial susceptibility testing, whole-genome sequencing, and quantitative polymerase chain reaction for assays of ampC, ompC and ompF transcripts. Forty-two ECC blood isolates were categorized into RCS and carbapenem-susceptible groups based on imipenem minimum inhibitory concentration. RCS ECC blood isolates belonged to distinct species and sequence types and produced varying class C β-lactamases. The E. roggenkampii, E. asburiae, and E. bugandensis isolates belonged only to the RCS group. Some E. hormaecheii ssp. steigerwaltii isolates of the RCS group exhibited AmpC overexpression caused by amino acid substitutions in AmpD and AmpR along with ompF gene downregulation. These findings suggest that non-carbapenemase-producing RCS ECC blood isolates are genetically diverse.

阴沟肠杆菌复合体 (ECC) 是菌血症的最常见原因之一，并导致不良的临床结果。本研究的目的是通过琼脂稀释抗菌药敏试验、全基因组测序和定量聚合酶链阐明日本非产碳青霉烯酶的还原型碳青霉烯类 (RCS) ECC 血液分离株的抗菌药敏谱和遗传背景ampC , ompC和ompF测定的反应成绩单。根据亚胺培南最小抑制浓度，将 42 种 ECC 血液分离物分为 RCS 和碳青霉烯敏感组。RCS ECC 血液分离物属于不同的物种和序列类型，并产生不同的 C 类 β-内酰胺酶。E. roggenkampii、E. asburiae和E. bugandensis分离株仅属于 RCS 组。一些E. hormaecheii ssp。RCS 组的steigerwaltii分离株表现出由 AmpD 和 AmpR 中的氨基酸取代以及ompF基因下调引起的 AmpC 过表达。这些发现表明，不产生碳青霉烯酶的 RCS ECC 血液分离物具有遗传多样性。