Topic：When bacteria adhere to a surface, there is more to it than counting numbers
l Full Professor and Head Department of Biomedical Engineering at the W.J. Kolff Institute, University Medical Center and University of Groningen, Netherlands
l Director-owner of a consulting company: Scientific and Applied Surface Advice
l Editor: Colloids and Surfaces B: Biointerfaces
Professor Busscher is an expert in biomaterials, biomedical engineering and microbiology. His research interests include physico-chemistry of the interactions of biological components (proteins, cells, microorganisms) with materials; prevention of biomaterial-associated infections through surface modification; prevention of infection of tissue-engineered constructs, etc.
Traditionally, bacterial adhesion is considered to be the counting of numbers of adhering bacteria on a substratum surface. Relations have been sought between numbers of adhering bacteria and physico-chemical properties of substratum surfaces, that more often did not exist than that they were actually found. However, there is more to “bacterial adhesion” than counting numbers.
The forces with which bacteria adhere play a pivotal role inmaking bacteria realize they left their planktonic state and become adherent, which starts a cascade of events that can lead to the expression of various genes, production of extracellular matrix components or in case of very strong forces: cell death.
AFM measurements as well as a new technique called “surface enhanced fluorescence” indicate that adhesion forces cause deformation of adhering bacteria through which they sense the properties of the substratum to which they adhere and upon which they eventually base their response to their adhering state.
QCM-D measurements have revealed that bacteria do not couple to a substratum surface as a particle but through a spring-like mechanism. Very interesting, the properties of such bacterial springs dictate the amplitude of random, Brownian motion-induced nanoscopic vibrations that adhering bacteria exhibit around their equilibrium position.
Both these elastic springs between adhering bacteria and between bacteria and substratum surfaces, combined with the properties of the extracellular matrix make bacterial biofilms to a visco-elastic mass. Stress relaxation measurements of bacterial biofilms and stress relaxation parameters derived can be employed not only to make an estimate of the matrix composition and biofilm structure, but also explain the difficulties involved in biofilm detachment and the penetration of antimicrobials through biofilms on a quantitative basis.
Truly have effective surface modifications and new materials to prevent bacterial adhesion and biofilm formation not yet been developed, despite all research efforts as they require more extensive knowledge of allphenomena that are going on when a bacterium adheres. Clearly, the multiple responses that bacteria have upon their disposal once adhering to a surface to defend themselves against environmental attacks of diverse nature, increase the complexity of the issue. The need for effective anti-bacterial surfaces is greatest in modern medicine, wherebiomaterials implants are more and more used for the restoration of function after trauma, wear or intervention surgery, yet the failure rate of biomaterial; implant due to infection is considered too high. Accounting for the multiple responses and interaction mechanisms that adhering bacteria utilize, may help in creating infection-resistant biomaterials for human use.