Aeromonas hydrophila resides in a variety of aquatic environments. Infections with A. hydrophila mainly occur after contact with fresh or brackish water. Nosocomial infections with A. hydrophila can also occur. A. hydrophila infections can be difficult to treat due to both intrinsic and acquired antimicrobial resistance (AMR) mechanisms. In 2018–19, we isolated multi-drug resistant (MDR) A. hyrodphila from two solid organ transplant patients with intra-abdominal infections. We aimed to characterize their AMR mechanisms and to determine their genetic relatedness to aid epidemiological investigation. We performed whole genome sequencing (WGS) using Illumina MiSeq and Nanopore MinIon on 3 A. hydrophila isolates, with one isolate from Patient A (blood) and two isolates from Patient B (abdominal and T-tube fluid, isolated 2 weeks apart). Phenotypic assays included: Broth Microdilution (BMD), Modified Hodge Test (MHT), Modified Carbapenem Inactivation Method (mCIM), and EDTA Carbapenem Inactivation Method (eCIM). Data analyses were performed using CLCbio and Geneious. AMR genomic analysis revealed that all three isolates possess chromosomally encoded genes including bla_OXA−12(oxacillinase), bla_cepS(AmpC), and bla_cphA7(metallo-beta-lactamase). All isolates tested strongly positive by MHT and mCIM, but only Patient B's second isolate (after 2 weeks of meropenem treatment) tested positive by eCIM. More intriguingly, Patient B's first isolate (before meropenem treatment) tested falsely susceptible to carbapenems by BMD, suggesting bla_cphA7 gene was not expressed constitutively. Phylogenetic analysis showed the two isolates from Patient B were highly similar with only 1 SNP difference. The isolate from Patient A only differed from Patient B's isolates by 35 and 36 SNPs, respectively, suggesting close genetic relatedness. Further epidemiological investigation is undergoing. We report the first cases of CphA-mediated carbapenem resistant A. hydrophila in the U.S. It is concerning that 1 out of 3 isolates tested falsely susceptible to carbapenems by BMD despite clear carbapenemase production shown by strongly positive MHT and mCIM. In both cases, meropenem was initially used to treat the patients. Clinicians and microbiologists in the US should be aware of the emerging MDR Aeromonas nosocomial infections and the potential false carbapenem susceptible results due to CphA-type carbapenemase, which may be induced during treatment.

嗜水气单胞菌居住在各种水生环境中。感染亲水曲霉主要发生在接触淡水或微咸水之后。医院感染亲水曲霉 也会发生。 亲水曲霉由于内在的和获得性的抗菌素耐药性（AMR）机制，感染可能难以治疗。在2018-19年度，我们隔离了多药耐药（MDR）嗜水气单胞菌来自两名患有腹腔内感染的实体器官移植患者。我们旨在表征其AMR机制并确定其遗传相关性，以协助流行病学调查。我们使用Illumina MiSeq和Nanopore MinIon在3上进行了全基因组测序（WGS）亲水曲霉分离株，其中一种来自患者A（血液），另一种来自患者B（腹部和T管液，分离2周）。表型分析包括：肉汤微稀释（BMD），改良的Hodge检验（MHT），改良的碳青霉烯灭活方法（mCIM）和EDTA碳青霉烯灭活方法（eCIM）。使用CLCbio和Geneious进行数据分析。AMR基因组分析表明，所有三个分离株均具有染色体编码的基因，包括bla_OXA-12（奥沙西林酶），bla_cepS（AmpC），以及 bla_phA7（金属-β-内酰胺酶）。所有分离株均通过MHT和mCIM测试呈强阳性，但只有患者B的第二个分离株（美洛培南治疗2周后）通过eCIM测试呈阳性。更有趣的是，患者B的第一个分离株（美罗培南治疗之前）通过BMD检测为对碳青霉烯类药物易感，表明bla_phA7基因不是组成性表达。系统发育分析表明，来自患者B的两个分离株高度相似，只有1个SNP差异。来自患者A的分离株与患者B的分离株分别分别具有35和36个SNP的差异，表明其密切的遗传相关性。正在进行进一步的流行病学调查。我们报告了首例CphA介导的碳青霉烯耐药亲水曲霉在美国，尽管MHT和mCIM呈强阳性表现出明显的碳青霉烯酶产生，但BMD检测出的3个分离株中有1个对碳青霉烯类药物易感。在这两种情况下，美罗培南最初都用于治疗患者。美国的临床医生和微生物学家应注意新兴的MDR气单胞菌 CphA型碳青霉烯酶引起的医院感染和潜在的假碳青霉烯易感性结果，可能在治疗过程中诱发。