Abstract
Antimicrobial resistance (AMR) has emerged as one of the most pressing global health challenges, compromising the efficacy of available antibiotics and leading to increased morbidity, mortality, and economic burden worldwide. Among resistant pathogens, Escherichia coli and Klebsiella pneumoniae producing New Delhi metallo-β-lactamase (NDM) enzymes have gained critical importance due to their ability to hydrolyze nearly all β-lactam antibiotics, including carbapenems, and the new cephalosporin, Cefiderocol. Understanding the molecular mechanisms driving resistance in these organisms is essential for guiding treatment strategies and developing new diagnostic approaches.This thesis investigates the mechanisms underlying β-lactam resistance in clinical isolates of E. coli and K. pneumoniae, with emphasis on the relationship between blaNDM expression and porin alterations. Whole-genome sequencing (WGS) was used to identify mutations within the blaNDM gene, its promoter region, and associated porin genes. Quantitative reverse transcription PCR (qRT-PCR) was performed to determine the relative expression of blaNDM , and results were correlated with the minimum inhibitory concentrations (MICs) of carbapenem antibiotics and cefiderocol. Structural modeling of OmpC porin and Western blotting analyses were used to evaluate alterations in protein expression and structure.
The findings revealed that enhanced blaNDM expression, together with mutations or loss of porin channels, produced a synergistic effect leading to elevated resistance to carbapenems. These results provide evidence that resistance in NDM-producing Enterobacterales is not solely enzyme-driven but is influenced by permeability alterations in the bacterial outer membrane.
Overall, this study contributes to a deeper understanding of the genetic and structural determinants of β-lactam resistance and highlights the importance of molecular based research in combating the global spread of carbapenem-resistant Enterobacterales.