Phenotypic and genotypic detection of carbapenemase production among gram negative bacteria isolated from hospital acquired infections.

Objectives: To identify the carbapenemase producing Gram-negative bacteria (GNB) by phenotypic methods and to confirm the presence of resistant genes using real-time polymerase chain reaction (PCR).

Methods: This was a prospective study carried out at the Department of Microbiology, Sri Venkata Sai Medical College and Hospital, Mahabubnagar, India, from March 2018-2021. All samples were screened for carbapenem resistance by disc diffusion method and the VITEK2 compact system (bioMérieux, France). Detection of carbapenemase was carried out using RAPIDECCARBA NP test (Biomeriux Private Limited, South Delhi, India), screening for metallo-β-lactamases (MBL) was carried out by double disk synergy test (DDST), and genotypic characterization by real-time PCR.

Results: Among the 1093 Gram-negative bacilli identified, 220 (17.0%) were resistant to carbapenems by both tested methods. Carbapenemase detection using the RAPIDECCARBA NP test indicated that 207 (94.0%) were carbapenemase producers, of which 189 (91.2%) were MBL producers. The most common carbapenemase genes identified were New Delhi metallo-β-lactamase (NDM; 47.3%), followed by the co-existence of genes in combination of NDM, with Verona integron-mediated metallo-β-lactamase (VIM; 39.6%), VIM and oxacillin hydrolyzing enzymes-48 (OXA-48; 4.3%), and OXA-48 (1.4%).No gene of active on imipenem, carbapenemase, VIM, or OXA-48 alone was detected.

Conclusion: This study suggests routine carbapenem resistance testing among multi-drug resistant-GNBs, as most of these infections occur in hospitals. In addition, there is a possibility that these highly antibiotic-resistant genes could spread to other bacteria resulting in further dissemination.