NDM-1-and OXA-23-producing Acinetobacter baumannii in wastewater of a Nigerian hospital

Carbapenem-resistant Acinetobacter baumannii spp. are increasingly important pathogens with limited treatment options, and there is limited knowledge on the environmental factors contributing to their spread. We determined the occurrence of carbapenem-resistant A. baumannii in hospital wastewater and their phylogenetic relationships with clinical A. baumannii isolates. Grab samples of raw and treated hospital wastewater were collected monthly at the University College Hospital, Ibadan, Nigeria, between March 2021 and February 2022. Acinetobacter baumannii strains were selectively isolated and identified using VITEK2, and their whole genomes were sequenced on an Illumina platform. We performed antimicrobial susceptibility testing and in silico genomic characterization of the strains and determined their phylogenetic relationships to previously characterized clinical A. baumannii strains from Nigeria. A. baumannii complex isolates were recovered from wastewater throughout the study. Of the 82 isolates identified based on whole-genome sequences, 77 were A. baumannii. A. baumannii isolates had high resistance rates (>= 48.1%) to 10 of 12 antimicrobials tested, and majority (42/77, 54.5%) were resistant to carbapenems, with bla NDM-1 being the most common (24/77, 31.2%) carbapenem resistance gene detected, followed by bla OXA-23 (n = 22, 28.6%). There was no statistically significant difference in carbapenem resistance rates or carbapenem gene carriage between the raw and treated wastewater isolates. Most of the isolates belonged to novel or sparsely described lineages, some of which were closely related to clinical isolates. The release of inadequately treated hospital wastewater into the environment may contribute to the increased spread of carbapenem-resistant and clinically important A. baumannii lineages in Ibadan, Nigeria.