Dissecting the mechanisms of resistance to novel antimicrobial agents among carbapenemase-producing strains of Enterobacterales

Antimicrobial resistance is among the top 10 global health crisis, highlighting the urgent need for new strategies and therapies to overcome AMR. This project is focused on investigating the role of outer membrane permeability (OM) in resistance among clinical isolates of Escherichia coli (EC) and Klebsiella pneumoniae (KP), both classified as top-priority AMR pathogens. A 69 KP isolates from past three years and eight EC isolates obtained from a previous studies were included in the study. The isolates were tested against β-lactam/β-lactamase inhibitor (BL-BLI) combinations: aztreonam-avibactam (ATM-AVI), cefepime-zidebactam (FEP-ZID), and a siderophore cephalosporin: cefiderocol (FDC), by broth microdilution (BMD) and disk diffusion (DD). OM permeability assays were conducted on the KP isolates resistant to BL-BLI agents and the EC isolates were tested against ATM and ATM-AVI, to compare the uptake under treated and untreated conditions. Gene expressions studies were performed for EC porin (ompF, ompC) and efflux pump genes (acrA, acrB, tolC, mdtA). It was found that the KP isolates showed highest resistance to FDC, followed by ATM-AVI, with no resistance observed against FEP-ZID. The OM permeability results showed a slight alteration in the uptake among KP and EC isolates treated with ATM, whereas a decreased uptake was seen in EC isolates exposed to ATM-AVI. The gene expression studies revealed that the porin and the efflux pumps were expressed independently of the antibiotic treatment. The study suggested that the resistance observed among the clinical isolates was not primarily due to permeability changes, indicating involvement of alternative underlying mechanisms.