Whole genome Sequencing Reveals Enterobacter hormaechei as a key Bloodstream Pathogen in six tertiary care hospitals in southwestern Nigeria.

Enterobacter spp. are an important cause of healthcare-associated bloodstream infections uncommonly reported in Africa. This study used whole genome sequencing (WGS) to characterise Enterobacter spp. from hospitals in Nigerias antimicrobial resistance (AMR) surveillance system. Blood-culture isolates of Enterobacter from six such tertiary-care hospitals recovered between 2014 and 2020 were re-identified and antimicrobial susceptibility-tested using VITEK2. Illumina technology provided whole genome sequences for genome nomenclature, antimicrobial resistance gene prediction, Single Nucleotide Polymorphism (SNP) phylogeny, and multi-locus sequence typing via publicly available bioinformatics pipelines. Initial biochemical delineation often misclassified Enterobacter, necessitating whole-genome sequencing for accurate classification. Among 98 Enterobacter received, Enterobacter hormaechei subspecies xiangfangensis predominated (43), followed by other E. hormachei subspecies (18), E. cloacae (26), E. roggenkampii (4), E. bugandensis (3), E. kobei (2), E. asburiae (1) and E. cancerogenous (1). Cephalosporins, aminoglycoside, chloramphenicol, macrolide, and carbapenem resistance in E. hormaechei was attributed to known resistance genes. They belonged to clusters III, IV, and VIII based on hsp60 typing and clades A, B, C, and D according to Sutton and Cos nomenclature. These isolates and other Enterobacter species recently reported from Nigeria reveal extensive E. hormaechei diversity, as well as clusters representing potential outbreaks. Enterobacter hormaechei, often misidentified and rarely reported from Nigeria, is this studys most common blood culture isolated Enterobacter spp. Uncovering underappreciated species as important bloodstream pathogens and retrospective detection of likely outbreaks emphasise the value of genomic surveillance in resource-limited settings. DATA SUMMARYAll sequence reads were submitted to the European Nucleotide Archive (ENA) under the project ID PRJEB29739 (https://www.ebi.ac.uk/ena/browser/view/PRJEB29739). Accessions can be found in Table S1. IMPACT STATEMENTAccurate identification of Enterobacter is essential in healthcare settings as misidentification can lead to selecting antimicrobials to the genus is intrinsically resistant resistant before susceptibility testing results are available. Also, misidentification can compromise microbiology support for infection prevention and control. We show that E. hormaechei, which is never reported from clinical laboratories in Nigeria, is frequently misidentified using conventional methods like tube- or strip biochemical testing and VITEK systems. Whole genome sequence data demonstrates that E. hormaechei and E. cloacae are the most common Enterobacter isolated from bloodstream infections in Nigeria. Enhanced identification methods for surveillance play pivotal roles in improving patient care, optimising antibiotic stewardship, and combating the evolving challenges posed by this pathogen. Overall, this study reveals the effectiveness of WGS in correctly identifying this important pathogen.