Phenotypic and genotypic characterization of carbapenem-resistant gram-negative bacilli pathogens from hospitals in Ghana

In Ghana, surveillance efforts on antibiotic resistance so far have not covered carbapenem resistance. In this study, our aim was to apply phenotypic and genotypic methods to identify and characterize carbapenem-resistant (CR) Gram-negative bacteria from the hospital environment in Ghana. A collection of 3840 isolates of Gram-negative bacilli infections from various clinical specimens was screened for carbapenem resistance by disc diffusion for imipenem, meropenem, and doripenem. Minimum Inhibitory Concentration (MIC) of the CR isolates was determined by E-test for the three carbapenems. All the CR isolates were further screened for carbapenemase activity by modified Hodge and boronic acid disc synergy tests. The CR isolates were investigated for the presence of carbapenemase and extended-spectrum beta-lactamase genes by PCR and confirmed by sequencing. The overall prevalence of CR isolates was 2.9% (111/3840). Based on the disc diffusion test, prevalence of resistance to carbapenems were doripenem (75%), imipenem (66.7%), and meropenem (58%). The highest measurable MIC levels (≥32 μg/mL) were observed in 56.8% of CR isolates with the nonfermenters, Pseudomonas aeruginosa (24.3%) and Acinetobacter species (18.9%), disproportionately represented. Phenotypic identification of carbapenamase activity occurred in 18.9% of the CR isolates by the modified Hodge test and 2.7% by Boronic acid disc synergy test; 21.6% exhibited carbapenemase production by both methods. All the CR isolates carried ESBL genes (blaTEM and blaSHV), whereas 23.4% were carriers of carbapenemase genes, of which 14.4% were blaNDM-1, 7.2% blaVIM-1, and 1.8% blaOXA-48. Phylogenetically, the CR isolates were diverse and showed limited relatedness to isolates from other geographical regions.