Abstract
Phenotypic diversity in bacterial flagella-induced motility leads to complex collective swimming patterns, appearing as traveling bands with transient locally enhanced cell densities. Traveling bands are known to be a bacterial chemotactic response to self-generated nutrient gradients during growth in resource-limited microenvironments. In this work, we studied different parameters of Escherichia coli (E. coli) collective migration, in particular the quantity of bacteria introduced initially in a microfluidic chip (inoculum size) and their exposure to antibiotics (ampicillin, ciprofloxacin, and gentamicin). We developed a hybrid polymer-glass chip with an intermediate optical adhesive layer featuring the microfluidic channel, enabling high-content imaging of the migration dynamics in a single bacterial layer, i.e., bacteria are confined in a quasi-2D space that is fully observable with a high-magnification microscope objective. On-chip bacterial motility and traveling band analysis was performed based on individual bacterial trajectories by means of custom-developed algorithms. Quantifications of swimming speed, tumble bias and effective diffusion properties allowed the assessment of phenotypic heterogeneity, resulting in variations in transient cell density distributions and swimming performance. We found that incubation of isogeneic E. coli with different inoculum sizes eventually generated different swimming phenotype distributions. Interestingly, incubation with antimicrobials promoted bacterial chemotaxis in specific cases, despite growth inhibition. Moreover, E. coli filamentation in the presence of antibiotics was assessed, and the impact on motility was evaluated. We propose that the observation of traveling bands can be explored as an alternative for fast antimicrobial susceptibility testing.
Highlights
Bacteria can sense a vast range of environmental signals.Decades of studies on the mechanisms underlying selfpropelled oriented bacterial swimming toward preferred niches for colonization, commonly known as chemotaxis, have elucidated pathways of chemosensory signal transduction and response regulation that affect bacterial active motion[1,2,3]
Considering the typical inoculum size of 3 × 105 CFU/mL used in our assays and the low volume of ~0.36 nL of the channel portion observed, less than 1 bacterium is expected to be found in the field of view (FOV)
Higher inoculum size leads to faster nutrient consumption and earlier nutrient depletion compared to lower inoculum size
Summary
Bacteria can sense a vast range of environmental signals.Decades of studies on the mechanisms underlying selfpropelled oriented bacterial swimming toward preferred niches for colonization, commonly known as chemotaxis, have elucidated pathways of chemosensory signal transduction and response regulation that affect bacterial active motion[1,2,3]. Liu et al Microsystems & Nanoengineering (2021)7:86 public health system is currently facing[7] In this context, fast antimicrobial susceptibility testing (AST), which is essential for the provision of the correct antimicrobials, is a key tool to counteract AMR propagation[8]. Microfluidic high-throughput platforms incorporating chips with (sub)micrometer features, which enable the precise handling and observation of single-cell organisms or small microbial colonies, have helped reveal fundamental aspects of bacterial life, cell-cell interactions and population dynamics[9,10,11]. Microfluidic chip assays enable accurate imaging and tracking of bacterial populations with single-cell resolution[12]. In the field of plant biology, Massalha et al developed a microfluidic device enabling precise dynamic imaging and tracking of root-bacteria interactions[18]. Onchip control of microenvironmental conditions was used to study microbial taxis with respect to a range of physical parameters, including temperature, magnetic field or light sensitivity[19]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
