Characterisation of carbapenem-resistant Gram-negative organisms from clinical specimens in Yola, Nigeria

•Screening of 1741 specimens identified 119 (6.8%) carbapenem-resistant bacteria.•PCR revealed that blaNDM and blaVIM genes accounted for 28.6% of carbapenem resistance.•Phenotypic ESBL or AmpC accounted for 16.0% of resistance.•The resistance mechanism could not be identified in about two thirds of the isolates. This study aimed to identify carbapenem-resistant Gram-negative bacteria from clinical specimens of patients in Yola, Nigeria. Routine clinical specimens were screened for the presence of carbapenem-resistant Gram-negative bacteria using chromogenic agar plates. Susceptibility of all presumptive isolates to carbapenems was tested by MIC and disk diffusion methods. Real-time PCR was used to test for the presence of carbapenemase genes. Screening of 1741 clinical specimens yielded 119 (6.8%) presumptive carbapenem-resistant Gram-negative bacteria. Antimicrobial susceptibility testing confirmed carbapenem resistance in 105 of these isolates. New Delhi metallo-β-lactamase (blaNDM) gene was detected in 26 isolates and Verona integron-encoded metallo-β-lactamase (blaVIM) gene was detected in four. The mechanism of resistance could not be identified in approximately two thirds of the carbapenem-resistant isolates. While blaNDM and blaVIM accounted for 28.6% of the resistance seen, further molecular-based studies are needed to characterise the other mechanisms of carbapenem resistance in these isolates.