Nosocomial cluster of patients infected with imipenemase-1-producing Enterobacter ludwigii.

Introduction. Imipenemase (IMI) enzymes are an uncommon class A carbapenemases that have been isolated from aquatic environments and, occasionally, from clinical isolates of Enterobacterales.Aim. We describe a cluster of three patients infected by IMI-1 carbapenemase-producing Enterobacter ludwigii (IMI-1-Elud) in a tertiary university hospital in Gran Canaria, Spain.Methodology. Antimicrobial susceptibility was determined using the Vitek2 AST-N355 card and antibiotic gradient strips. The modified carbapenem inactivation method (CIM) test was performed in cases where the ertapenem MIC value was higher than 0.125 mg l^-1. The carbapenemase was identified by PCR and DNA microarray and later characterized by whole-genome next-generation sequencing (NGS) with Illumina.Results. Three patients presented thoracic or abdominal infections caused by IMI-1-Elud ST1677 from 14 June 2022 to 14 July 2022. All patients underwent at least one gastroscopy during their admission, and two of them were located in adjoining rooms. Isolates were resistant to carbapenems, colistin and fosfomycin but susceptible to ciprofloxacin. IMI/NMC-A carbapenemase was detected by PCR and hybridization test and confirmed by NGS as IMI-1. All patients underwent at least one gastroscopy, and two of them were in nearby rooms. Patients showed microbiological and clinical improvement following focus drainage and targeted antibiotic treatment with a fluoroquinolone.Conclusions. This study reports the first documented global outbreak of patients infected with IMI-1-Elud. The source appeared to be related to endoscopes. Contact transmission may also have played a role. A screening method such as the modified CIM test is crucial for detecting less common carbapenemases that might not be identified by rapid molecular or immunochromatographic tests, as these often do not include bla _IMI genes, which could lead to the undetected dissemination of carbapenemase-producing Enterobacterales. Effective infection source control and targeted treatment are essential for achieving a favourable clinical outcome.