title: Biofilm cohesiveness measurement using a novel atomic force microscopy methodology.
abstract: Biofilms can be undesirable, as in those covering medical implants, and beneficial, such as when they are used for waste treatment. Because cohesive strength is a primary factor affecting the balance between growth and detachment, its quantification is essential in understanding, predicting, and modeling biofilm development. In this study, we developed a novel atomic force microscopy (AFM) method for reproducibly measuring, in situ, the cohesive energy levels of moist 1-day biofilms. The biofilm was grown from an undefined mixed culture taken from activated sludge. The volume of biofilm displaced and the corresponding frictional energy dissipated were determined as a function of biofilm depth, resulting in the calculation of the cohesive energy. Our results showed that cohesive energy increased with biofilm depth, from 0.10 +/- 0.07 nJ/microm(3) to 2.05 +/- 0.62 nJ/microm(3). This observation was reproducible, with four different biofilms showing the same behavior. Cohesive energy also increased from 0.10 +/- 0.07 nJ/microm(3) to 1.98 +/- 0.34 nJ/microm(3) when calcium (10 mM) was added to the reactor during biofilm cultivation. These results agree with previous reports on calcium increasing the cohesiveness of biofilms. This AFM-based technique can be performed with available off-the-shelf instrumentation. It could therefore be widely used to examine biofilm cohesion under a variety of conditions.
authors.affiliation: 3M Medical Division, 3M Center, Building 270-03-N-02, Saint Paul, MN 55144, USA. fahimou@mmm.com
authors.forename: Francois
authors.initials: F
authors.lastname: Ahimou
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Semmens
authors.forename: Paige J
authors.initials: PJ
authors.lastname: Novak
authors.forename: Greg
authors.initials: G
authors.lastname: Haugstad
mesh_terms: D001422:Bacterial Adhesion; D018441:Biofilms; D017276:Friction; D018625:Microscopy, Atomic Force / Q000379:methods*; D012722:Sewage / Q000382:microbiology
chemical_list: D012722:Sewage