Surface-Tethered Polymers to Influence Protein Adsorption and Microbial Adhesion

'Should I stay or should I go?' Bacterial attachment vs biofilm formation on surface-modified membranes

A number of techniques are used for testing the anti-biofouling activity of surfaces, yet the correlation between different results is often questionable. In this report, the correlation between initial bacterial deposition (fast tests, reported previously) and biofilm growth (much slower tests) was analyzed on a pristine and a surface-modified reverse osmosis membrane ESPA-1. The membrane was modified with grafted hydrophilic polymers bearing negatively charged, positively charged and zwitter-ionic moieties. Using three different bacterial strains it was found that there was no general correlation between the initial bacterial deposition rates and biofilm growth on surfaces, the reasons being different for each modified surface. For the negatively charged surface the slowest deposition due to the charge repulsion was eventually succeeded by the largest biofilm growth, probably due to secretion of extracellular polymeric substances (EPS) that mediated a strong attachment. For the positively charged surface, short-term charge attraction by quaternary amine groups led to the fastest deposition, but could be eventually overridden by their antimicrobial activity, resulting in non-consistent results where in some cases a lower biofilm formation rate was observed. The results indicate that initial deposition rates have to be used and interpreted with great care, when used for assessing the anti-biofouling activity of surfaces. However, for a weakly interacting 'low-fouling' zwitter-ionic surface, the positive correlation between initial cell deposition and biofilm growth, especially under flow, suggests that for this type of coating initial deposition tests may be fairly indicative of anti-biofouling potential.

Reduced bacterial deposition and attachment by quorum-sensing inhibitor 4-nitro-pyridine-N-oxide: the role of physicochemical effects

Surface-attached chemical groups that resist protein adhesion are commonly characterized as being hydrophilic, H-bond acceptors, non-H-bond donors, and electrically neutral. Quorum-sensing (QS) inhibitor 4-nitropyridine-N-oxide (4-NPO) that previously was found to decrease Pseudomonas aeruginosa biofilm formation possesses all of these characteristics, making this molecule an ideal antiadhesive compound. It was hypothesized that once 4-NPO adsorbs to either the solid surface or bacteria, resultant changes in the physical-chemical surface properties of the solid surface and bacteria will reduce the extent of bacterial adhesion. These physical-chemical effects take place prior to the commencement of already well-established QS biofilm-inhibition mechanisms. Bacterial adhesion experiments to silica conducted in quartz crystal microbalance with dissipation (QCM-D) and parallel plate flow cells demonstrated that 4-NPO reduces bacterial adhesion to silica-coated surfaces by the adsorption of 4-NPO to the silica surface as well to the outer membrane of both gram-negative P. aeruginosa PAO1 and gram-positive Staphylococcus aureus. 4-NPO effectively neutralizes both the bacterial and silica surface charge, and it is proposed that this neutralization of local surface charge heterogeneities by 4-NPO adsorption is the mechanism responsible for decelerating rates of bacterial deposition.