High incidence of carbapenemase-producing Pseudomonas aeruginosa clinical isolates from Lagos, Nigeria

Background: Carbapenem-resistant Pseudomonas aeruginosa strains are on the rise worldwide. This study characterized clinical isolates of P. aeruginosa from three Nigerian hospitals for carbapenem resistance. Methods: Strains isolated from wounds (n= 88), urine/catheter tips (n= 25), sputum/tracheotomy aspirates (n= 5), ear swabs (n= 4) and vaginal swabs (n= 1) were identified by MALDI-TOF and antibiotic susceptibility testing was performed using the VITEK 2 system. The genomic DNA of each isolate was subject to sequencing using Illumina and Oxford nanopore technology. Bioinformatics analyses were performed to detect antimicrobial resistance genes, clonal affiliations and phylogenetic relations of 123 non-duplicate P. aeruginosa isolates, whereas assembly of the nanopore reads using the plasmIDent pipeline enabled the identification of plasmids. Results: Forty-three percent of the isolates were resistant to all antibiotic categories tested. More than 40% of the isolates were resistant to the carbapenems imipenem and/or meropenem (39% and 44%, respectively). Among the meropenem-resistant isolates, 48 (89%) carried at least one carbapenemase gene. The predominant one was blaNDM-1 (n= 34), which conferred resistance to all five antibiotic categories and highly increased the MICs of both meropenem and imipenem. The other recurrent carbapenemase genes were blaVIM-2 (n= 4), and blaVIM-5-like (n= 11), which co-existed with blaNDM-1 in two isolates. Conclusions: The study revealed a high rate of carbapenem resistance and conjugative, broad host range plasmids carrying carbapenemase-encoding genes, especially the NDM-1 type, among isolates of P. aeruginosa. This may forebode the emergency of ubiquitous carbapenem resistance urging the implementation of infection control and antimicrobial stewardship strategies in Nigerian hospitals.