Detection and characterisation of carbapenem-resistant gram-negative bacilli infections in Ghana

In Ghana, little is known about the nature and spread of carbapenemases in carbapenemresistant (CR) pathogens. The aims of the present study were to detect carbapenemase activity by using simple phenotypic tests, molecular typing to characterise the resistance genes and to determine the relatedness of the CR isolates collected from different hospitals in the country. A total of 111 CR isolates were identified by disc diffusion susceptibility testing and the MIC E-test method. Phenotype-based methods including the modified Hodge test, boronic acid-disc synergy test, nitrocefin assays, plasmid analysis and sodium dodecylsulphate polyacrylamide gel electrophoresis for the expression of the outer membrane protein were performed for each of the CR isolates. Amplified DNA products were examined for common ESBL encoding genes (blaTEM-1 and blaSHV-1) and carbapenemase resistance genes (blaKPC-1, blaIMP-1, blaNDM-1, blaVIM-1 and blaOXA-48). Enterobacterial repetitive intergenic consensus (ERIC) by PCR technique was used to establish the relatedness of isolates. Overall, a carbapenem-resistant prevalence of 2.9% (111 of 3840) was detected from the total of Gram-negative bacterial pathogens. In MIC E-test assays, 56.8% of CR isolates showed complete resistance to imipenem, meropenem and ertapenem at ≥32 μg/ml, of which 24.3% were found in Pseudomonas aeruginosa isolates and 18.9% in Acinetobacter baumannii isolates. In all, no KPC-1 and IMP-1 genes were detected. Carbapenemase genes identified were blaNDM-1 in Acinetobacter baumannii isolates, blaVIM-1 in Pseudomonas species and blaOXA-48 was only present in Klebsiella pneumoniae isolates. None of the carbapenemase-positive gene carriers harboured two xviii or more of carbapenemase resistance genes. Transfer experiments revealed the possible spread of the resistance genes from pathogens to commensal organisms by conjugation. Close relatedness with co-occurrence of oprD loss was detected among a small number of carbapenemase resistance gene carrying isolates of Acinetobacter baumannii. This is the first report of the detection and characterisation of carbapenemase resistance genes in Ghana.