Cracking Antimicrobial Resistance
Understanding cell wall antibiotic action
Cell wall antibiotics are crucial for combatting the emerging wave of resistant bacteria. Yet, our understanding of antibiotic action is limited, as many strains devoid of all resistance determinants display far higher antibiotic tolerance in vivo than suggested by the antibiotic-target binding affinity in vitro. To resolve this conflict, we developed a comprehensive theory for the bacterial cell wall biosynthetic pathway and study its perturbation by antibiotics. It turned out that the closed-loop architecture of the lipid II cycle of wall biosynthesis features a highly asymmetric distribution of pathway intermediates, showing that antibiotic tolerance scales inversely with the abundance of the targeted pathway intermediate. We formalize this principle of minimal target exposure as an intrinsic resistance mechanism and predict how cooperative drug-target interactions can mitigate resistance. The theory accurately predicts the in vivo efficacy of various cell wall antibiotics in different Gram-positive bacteria and contributes to a systems-level understanding of antibiotic action.
The theory also helps us to understand how different active resistance mechanisms are orchestrated within the intricate cell envelope stress response network of bacteria. For instance, when challenging Bacillus subtilis with the cell wall antibiotic bacitracin, we find a high level of cross-regulation between the major resistance modules. To rationalize these data, an expansion of our theory for the lipid II cycle captures the complex interplay between these modules and the cell wall biosynthetic cycle and accurately predicts the minimal inhibitory bacitracin concentration in mutant cell lines deficient in different resistance modules. This highlights how bacterial resistance emerges from an interlaced network of redundant homeostasis and stress response modules.
Based on these insights our group seeks to break resistance by developing novel strategies to interfere with the resistance gene expression network, using tools from systems and synthetic biology available in our lab. The current focus is to target cell wall antibiotic resistance in Gram-positive bacteria, including the model organism B. subtilis and the human pathogen Enterococcus faecalis.
The lipid II cycle of Gram-positive bacteria is a prime target for antibiotics.
Piepenbreier H., Diehl A., and Fritz G. (2019), Minimal exposure of lipid II cycle intermediates triggers cell wall antibiotic resistance. Nature Communications, 10, 2733
Piepenbreier H., Sim A., Kobras C.M., Radeck J., Mascher T., Gebhard S. and Fritz G. (2020) From modules to networks: A systems-level analysis of the bacitracin stress response in Bacillus subtilis. mSystems, 5, e00687-19
Radeck J., Fritz G., Mascher T. (2017). The cell envelope stress response of Bacillus subtilis: From static signaling devices to dynamic regulatory network. Current Genetics 63, 79-90
Fritz G., Dintner S., Treichel N., Radeck J., Gerland U., Mascher T., Gebhard S. (2015). A new way of sensing: Need-based activation of antibiotic resistance by a flux-sensing mechanism. mBio 6, e00975-15
ECF σ factors play an important role in natural stress responses (top) and serve as ideal building blocks for the construction of synthetic gene expression programs to introduce temporal control in biosynthetic pathway activation (bottom).
Building orthogonal gene expression programs
Located in the iconic Bayliss Building on UWA Crawley campus, our lab provides and shares access to excellent in-house research infrastructure:
High-throughput liquid handling robotics facility including
Beckman & Coulter Echo 650 acoustic nanoliter dispenser
Integra Assist Plus microliter pipetting platform
Multiple microplate readers
Biomolecular interactions facility
Protein production and structure facility
Mass spectrometry facility
High-performance computer cluster