Proefschrift

Combating gram-negative resistance: targeting the cell envelope

This thesis examines strategies to address the global threat of antimicrobial resistance (AMR). Antimicrobial resistance poses an increasing global health risk, highlighting the need for new treatments against Gram-negative pathogens.

Auteur: N.C. Brüchle
Datum: 06 maart 2026
Links: Thesis in Leiden Repository

These bacteria possess a protective outer membrane and efflux mechanims that hinder conventional antibiotics. This thesis focuses on targeting the cell envelope, specifically the beta-barrel assembly machinery (BamA) and lipoprotein signal peptidase II (LspA). These essential pathways are more accessible than cytoplasmic targets and are less vulnerable to internal efflux mechanisms. We employed mRNA display using outer-membrane vesicles (OMVs) to identify peptides that bind to BamA in a native membrane environment. Additionally, we developed and evaluated nanobody-drug conjugates by linking a BamA-targeting nanobody (nanoE6) to polymyxin B nonapeptide (PMBN) to disrupt membrane integrity. We also evaluated a FRET-based biochemical assay, which proved to be a highly sensitive and robust tool for identifying LspA inhibitors like globomycin within complex natural product extracts. Finally, we examined the effect of the narrow-spectrum antibiotic cloxacillin on the growth of Gram-negative bacteria that produce various β-lactamases. Although cloxacillin is generally regarded as ineffective against Gram-negative bacteria, our results demonstrated that it can still influence their growth.