Candida albicans biofilm formation on peptide functionalized polydimethylsiloxane

In order to prevent biofilm formation by Candida albicans, several cationic peptides were covalently bound to polydimethylsiloxane (PDMS). The salivary peptide histatin 5 and two synthetic variants (Dhvar 4 and Dhvar 5) were used to prepare peptide functionalized PDMS using 4-azido-2,3,5,6-tetrafluoro-benzoic acid (AFB) as an interlinkage molecule. In addition, polylysine-, polyarginine-, and polyhistidine-PDMS surfaces were prepared. Dhvar 4 functionalized PDMS yielded the highest reduction of the number of C. albicans biofilm cells in the Modified Robbins Device. Amino acid analysis demonstrated that the amount of peptide immobilized on the modified disks was in the nanomole range. Poly-d-lysine PDMS, in particular the homopeptides with low molecular weight (2500 and 9600) showed the highest activity against C. albicans biofilms, with reductions of 93% and 91%, respectively. The results indicate that the reductions are peptide dependent

Prevention and eradication of microbial biofilms

Medical materials are frequently introduced in the human body. They consist of biocompatible polymers such as PDMS, to which micro-organisms easily adhere, resulting in the formation of biofilms. The first antibiofilm strategy was to try to prevent Candida albicans biofilm formation on PDMS. To this end two approaches were used, i.e. the modification of the PDMS surface by grafting of antimicrobial compounds and the incorporation of antimycotics in the bulk PDMS polymer. DMAEMA was covalently bound to PDMS and subsequently quaternized at the surface with alkyl chains of different length. Shorter alkyl chains yielded substantially lower C. albicans sessile cell counts in a dynamic biofilm model system (MRD) than longer ones. PEI grafted on PMMA or PDMS showed poor efficacy as to the inhibition of C. albicans biofilm development. Finally, PDMS was functionalized with cationic peptides. Dhvar 4-PDMS and Poly-D-lysine-PDMS (active moieties with molecular weight distributions of 1,000-4,000 and 4,000-15,000, respectively) yielded the highest reduction (> 90%) in the number of C. albicans biofilm cells. In a second experimental approach, we incorporated miconazole, nystatin, tea tree oil and zinc pyrithione in the PDMS polymer. Impregnated PDMS disks (prepared by immersion in a solution containing the antimycotic) yielded reductions in sessile cell counts of more than 90%. When the antimycotic was mixed with the PDMS compounds prior to vulcanization, an antibiofilm effect was only observed in a microtiter plate, due to the rapid release (burst effect) of the active compound in the small volume of a well. In the MRD, the antimycotic released from either an impregnated or medicated disk is washed away by the liquid flow. In a second antibiofilm strategy entitled “biofilm eradication”, the aim was to study the ability of NitrAdineTM, a disinfectant for oral hygiene to remove biofilms from polymeric materials. Under various conditions NitrAdineTM showed high activity (> 3 log units reduction) against biofilms of C. albicans and S. aureus, grown on PMMA disks in the MRD