title: High-level and novel mechanisms of carbapenem resistance in Gram-negative bacteria from tertiary hospitals in Nigeria.
abstract: To determine the occurrence and molecular basis of carbapenem resistance in Gram-negative bacteria from tertiary hospitals in Nigeria, 182 non-duplicate Gram-negative bacterial isolates were investigated for antimicrobial susceptibility, presence of carbapenemases (tested phenotypically and genotypically), random amplified polymorphic DNA (RAPD) typing, plasmid sizing and replicon typing. Minimum inhibitory concentrations of carbapenems showed a high degree of resistance, with 67 isolates (36.8%) being resistant to all carbapenems, of which 40 (59.7%) produced enzymes able to hydrolyse imipenem. PCR and sequencing identified only 10 isolates (5.5%) carrying known carbapenemase genes, including bla(NDM), bla(VIM) and bla(GES). The majority of phenotypically carbapenem-resistant and carbapenemase-producing isolates did not carry a known carbapenemase gene. Transconjugant or transformant plasmid sizes were estimated to be 115 kb for bla(NDM)- and 93 kb for bla(VIM)-carrying plasmids. These plasmids were untypeable for replicon/incompatibility and transferred various other genes including plasmid-mediated quinolone resistance (PMQR) genes and bla(CTX-M-15). Typing showed that the isolates in this study were not clonally related. There is a high level of carbapenem resistance in Nigeria. As well as the globally relevant carbapenemases (bla(NDM), bla(VIM) and bla(GES)), there are other unknown gene(s) or variant(s) in circulation able to hydrolyse carbapenems and confer high-level resistance.
authors.affiliation: Department of Biomedical Sciences, Ladoke Akintola University of Technology, Ogbomosho, Osogbo Campus, Nigeria; Antimicrobials Research Group, Immunity and Infection, Institute of Microbiology & Infection, University of Birmingham, Birmingham, B15 2TT, UK.
authors.forename: D O
authors.initials: DO
authors.lastname: Ogbolu
authors.affiliation: Antimicrobials Research Group, Immunity and Infection, Institute of Microbiology & Infection, University of Birmingham, Birmingham, B15 2TT, UK. Electronic address: m.a.webber@bham.ac.uk.
authors.forename: M A
authors.initials: MA
authors.lastname: Webber
mesh_terms: D001426:Bacterial Proteins / Q000032:analysis / Q000235:genetics; D015780:Carbapenems / Q000494:pharmacology*; D016000:Cluster Analysis; D003227:Conjugation, Genetic; D005838:Genotype; D006090:Gram-Negative Bacteria / Q000145:classification / Q000187:drug effects* / Q000235:genetics / Q000302:isolation & purification; D016905:Gram-Negative Bacterial Infections / Q000382:microbiology*; D006801:Humans; D006868:Hydrolysis; D015378:Imipenem / Q000378:metabolism; D008826:Microbial Sensitivity Tests; D058889:Molecular Typing; D009549:Nigeria; D010957:Plasmids / Q000032:analysis / Q000145:classification; D019105:Random Amplified Polymorphic DNA Technique; D017422:Sequence Analysis, DNA; D062606:Tertiary Care Centers; D014169:Transformation, Bacterial; D018440:beta-Lactam Resistance; D001618:beta-Lactamases / Q000032:analysis / Q000235:genetics
chemical_list: D001426:Bacterial Proteins; D015780:Carbapenems; D015378:Imipenem; D001618:beta-Lactamases; C063912:carbapenemase
keywords: Carbapenem; Gram-negative bacteria; Nigeria; Resistance