Changes in bacterial adherence in different flow conditions

Fluid flows are dominant features of the environments of many bacterial species, yet the interactions between flow, surface association, and colonization factors remain largely underexplored. In dynamic bacterial populations, there are multiple interactions that occur between different length scales, from gene expression in single cells to collective behaviors or spatial effects in biofilm communities. With the addition of flow environments, we can further understand these emergent behaviors. One specific example is infective endocarditis, in which bacterial pathogens have long been known to preferentially colonize the heart valves with the greatest flow rates. The mechanisms underlying this important yet paradoxical behavior are unknown. To begin to address these questions I have developed a system for studying the effects of flow on colonization of several endocarditis-inducing pathogens including Staphylococcus aureus MRSA, Enterococcus faecalis and Streptococcus pneumoniae. In microfluidic devices I observed the bacteria growing from single cells to microcolonies and found a counter-intuitive result in which bacteria under high flow conditions colonized the surface better than those same species in low flow conditions. Under low flow, robust colonies form and disperse over the experimental run, whereas little dispersal is seen in the high dispersal case. My current focus is to determine both the biophysical and molecular mechanisms of this surprising bacterial adherence behavior.