DEVELOPING A NONDESTRUCTIVE TECHNIQUE FOR MEASURING BULK RHEOLOGY OF PSEUDOMONAS AERUGINOSA BIOFILM

Bacterial cultures, when under appropriate conditions, will grow into a biofilm. This weak hydrogel, composed of a complex conglomeration of bacterial clusters and extrapolymeric substances, serves to protect and insulate the bacteria from mechanical disturbances and environmental perturbations that may include antibiotics. Measuring the bulk rheology of the biofilm provides a quantitative description of the macroscopic structural integrity of the soft solid, which can be used to evaluate the efficacy of techniques that are often directed at their removal or prevention. Techniques for measuring the rheology of biofilms vary significantly, ranging from filtering or scraping the biofilm from its growth medium to attempting to grow the biofilm directly on the geometry of the rheometer. In this study, we developed a protocol for measuring the bulk rheology of a biofilm that was grown in a liquid medium. By keeping the biofilm intact from its growth phase through its rheological measurement, this method allows the mechanical strength of the biofilm to be probed without compromising its integrity. Presented in the form of case studies, the results from this study confirmed the gel-like structure of the biofilm of the wild-type strain of Pseudomonas aeruginosa (PAOi). The flexibility of this protocol was shown by varying the incubation time of the biofilm from 4 to 9 days, providing a bulk elastic modulus that varied over two orders of magnitude and a yield stress that varied by an order of magnitude. Finally, in an attempt to demonstrate the fragility of biofilm, measurements were also taken on samples that were simply transferred from their incubated Petri dish to the rheometer. Results from the mechanical robustness of the biofilm are highlighted to emphasize the importance of understanding and addressing the mechanical strength of the biofilm system before attempting to remove the bacterial contamination through chemical or mechanical means.