The A226D Mutation of OmpC Leads to Increased Susceptibility to β-Lactam Antibiotics in Escherichia coli

Bacterial resistance to antibiotics can lead to long-lasting, hard-to-cure infections that pose significant threats to human health. One key mechanism of antimicrobial resistance (AMR) is to reduce the antibiotic permeation of cellular membranes. For instance, the lack of outer membrane porins (OMPs) can lead to elevated AMR levels. However, knowledge on whether mutations of OMPs can also influence antibiotic susceptibility is limited. This work aims to address this question and identified an A226D mutation in OmpC, a trimeric OMP, in Escherichia coli. Surveillance studies found that this mutation is present in 50 E. coli strains for which whole genomic sequences are available. Measurement of minimum inhibition concentrations (MICs) found that this mutation leads to a 2-fold decrease in MICs for beta-lactams ampicillin and piperacillin. Further survival assays confirmed the role this mutation plays in beta-lactam susceptibility. With molecular dynamics, we found that the A226D mutation led to increased overall flexibility of the protein, thus facilitating antibiotic uptake, and that binding with piperacillin was weakened, leading to easier antibiotic penetration. This work reports a novel mutation that plays a role in antibiotic susceptibility, along with mechanistic studies, and further confirms the role of OMPs in bacterial tolerance to antibiotics.