Antibiotic tolerance of biofilms emerging from multicellular effects of antibiotic efflux

Introduction: Biofilms are multicellular assemblages of bacteria living in a self-produced extracellular matrix. One characteristic of biofilms is that they are difficult to kill. Different mechanisms, like the development of highly tolerant persister cells or increased expression of efflux pumps, which pump certain antimicrobials out of the cell, make them tolerant.
Goals: The overall project goal is to develop a predictive model for efflux-mediated antimicrobial multicellular assemblies.Our central hypothesis is that efflux pump activity causes emergent antimicrobial tolerance of multicellular bacterial populations, through the interplay of efflux-mediated spatial interactions and efflux-linked persistence.
Methods & Results: To test the hypothesis, we are combining computational modelling with information gained from 3 types of multicellular assemblages, i.e. colonies on agar, multicellular populations grown in a monolayer microfluidic device, and 3D biofilms grown in flow chambers. We are currently generating strains that differ in their levels of efflux activity. In parallel the strains are characterized in terms of growth, minimum inhibitory concentration of different antimicrobial substances, colony morphology, and biofilm formation ability. The strains will be mixed and then cultivated together in the 3 model systems. In colonies, the link between colony structure and spatial patterns of gene expression will be characterized. Experiments in microfluidic devices will be used to determine the interactions range of cells with high efflux activity on neighboring susceptible cells, as well as to analyze the correlation between efflux and persister formation. The results will be used to construct individual-based models that predict the effect of efflux on biofilm structure and antimicrobial tolerance. Flow chamber 3D biofilms will be generated to test the model predictions.
Summary: Using combination of computational modelling and lab experiments with multicellular assemblages, we want to shed light on the interplay between spatial biofilm organization, multidrug efflux and antimicrobial tolerance.