Molecular characterization and antibiogram of the carbapenemase gene variants in clinical strains of Pseudomonas aeruginosa

Abstract

Background: Carbapenemase-producing Pseudomonas aeruginosa (CPPA) is a substantial clinical concern because it jeopardizes therapeutic choices. This study characterizes the gene variants of CPPA and report its antibiogram. Methods: CPPA was isolated prospectively from diverse clinical sources in a tertiary care setting using a routine microbiological approach. Carbapenem-resistant P. aeruginosa strains were phenotypically identified using the modified carbapenem inactivation (mCIM) method. Minimum inhibitory concentration (MIC) breakpoints of several antibacterial drug groups were determined using broth microdilution methods and the MicroScan WalkAway plus system. Carbapenemase gene variants blaNDM, blaVIM, blaOXA,blaGES, and blaIMP were amplified using polymerase chain reaction (PCR), and the purified gene products were sequenced. Results: Seventy-one P. aeruginosa-infected cases were found, with 47 (66.2%) carrying CPPA; 46.8% of the latter were significantly associated with intensive care units (p = 0.03). CPPA was frequently detected in wound swabs (13; 27.7%), sputum (11; 23.4%), and blood (9; 19.1%). All strains were multidrug-resistant (MDR), and several were extensively drug-resistant. MIC50 and MIC90 breakpoints of all antibiotics, except colistin, were within the resistance range. MIC90 breakpoints of aztreonam, amikacin, cefepime, and piperacillin-tazobactam were > 512 µg/mL. The multiple antibiotic resistance index (MARI) was remarkably high, with a range of 0.38–0.92. The most commonly detected carbapenemase genes were blaVIM (74%), blaNDM−1 (19%), blaOXA−23 (14.9%), and blaGES (10.6%), while 12 of 47 strains co-harbored different combinations of carbapenemase gene variants. Conclusion: A large proportion of CPPA strains carried the blaVIM gene variant, indicating intimidating health problems and emphasizing the need for extensive surveillance and antibiotic stewardship.