Abstract

Antibiotic resistance poses a major threat to public health. While the vast majority of antibiotic research focuses on homogeneous cultures, bacteria commonly live in surface-attached communities where they are exposed to steep chemical gradients. In this biolunch talk I will show you the behavior of bacteria in spatial gradients of antibiotics by tracking thousands of individual cells as they colonize the surface in developing biofilms. Surprisingly, these experiments reveal that cells use pili-based (‘twitching’) motility to move towards higher concentrations of antibiotics. While antibiotic gradients trigger sharp variations in cell density across the surface, our data suggest that chemotaxis is a direct response to antibiotics and not simply driven by secondary de novo gradients in nutrients or secreted compounds. Moreover, within 20 hours, migrating cells reach and withstand antibiotic concentrations one thousand times higher than expected from their MIC (minimal inhibitory concentration). We find no evidence for genetic resistance and instead physiological resistance (tolerance) appears key for this striking phenotype. I will finish by discussing how we can interpret these unexpected results using microbial ecology and evolution.