Cohesive Strength and Detachment of Bacterial Biofilms
CoPIs: Raymond M. Hozalski and Phil Stewart (Montana State University and the Center for Biofilm Engineering)
Funding Agency: National Science Foundation
The goal of this fundamental research project is to develop effective strategies for controlling and removing microbial biofilms based on an improved understanding of the mechanisms of cohesion of the biofilm extracellular matrix. Biofilms are dense agglomerations of bacterial or fungal cells that attach to wetted surfaces. These cells are held together by a mixture of highly hydrated biopolymers that the cells themselves secrete. Biofilms are responsible for troublesome fouling in water distribution systems and industrial equipment and for persistent infections in medicine and dentistry. Unfortunately, the use of antimicrobial agents to remove biofilms is frustrated by the reduced susceptibility of microorganisms in biofilms. Mechanical removal is effective, but requires physical access to the biofilm and can be labor intensive or involve equipment downtime. This research represents a paradigm shift in approach to controlling unwanted biofilms from “kill” and “scrape” to weakening the biofilm structure and promoting detachment.
For this work, we will use a
micro-mechanical technique we developed for directly measuring the cohesive strength
of biofilms based on the observed deflection of a
cantilevered glass micro-pipette as it separates a particle from the
intact biofilm, or separates a biofilm fragment captured between two
pipettes (Figure 1 below, see a previous research webpage for more information). We will also use flow cells (Figure 2) for non-invasive viewing biofilm behavior and detachment.
Figure 1 . Micro-cantilever device for testing the tensile strength of detached biofilms and flocs. a) Top view (detail) showing cantilever and capture pipette. Cantilever is glued onto support; capture pipette is mounted on a micromanipulator. b) Side view and schematic of image capture device. Surface tension holds water (hatched area) on top of the raised platform. Capture pipette, which would enter the platform area normal to the page, is omitted for clarity. The base for the device is a standard 2.54 x 7.62 cm microscope slide. A test is performed by first immobilizing a biofilm sample between the cantilever and capture pipettes and then withdrawing the capture pipette until breakage occurs. The measured deflection of the pre-calibrated cantilever is used to compute the force applied.
Figure 2. Glass capillary biofilm reactor system. Biofilms are grown under continuous-flow conditions. The glass tubes have a square cross section, allowing direct microscopic observation of biofilm growing on the inside of the tube. The apparatus consists of a vented medium feed carboy (4 liter capacity), a flow break, a filtered air entry, a peristaltic pump, the capillary and flow cell holder, an inoculation port, and a waste carboy. These components are connected by silicone rubber tubing.