Chemotactic Adaptation of Escherichia coli under Levofloxacin Stress

Understanding how bacteria respond to antibiotic gradients is crucial for unravelling the mechanisms underlying antimicrobial resistance. Here, we investigate the spatiotemporal chemotactic and motility behaviour of Escherichia coli in response to levofloxacin (LVX) gradients using a microfluidic capillary-based system. By analysing cellular trajectories through velocity autocorrelation and mean squared displacement (MSD) metrics, we quantify changes in persistence time, persistence length, and motility regimes across uniform and gradient antibiotic conditions. Our results reveal that E. coli displays concentration and gradient-dependent transitions between attractant, repellent, and non-sensing states. Notably, under steep gradients, bacteria exhibit biphasic responses, including adaptive shifts from attractant to non-sensing behaviours. Increasing LVX concentration suppresses directional motility and superdiffusiveness, as indicated by decreased autocorrelation amplitudes and α exponents. These findings highlight the dynamic and context-dependent nature of bacterial chemotaxis under antibiotic stress and provide critical biophysical insights into transient resistance mechanisms.