Protein antimicrobial barriers to bacterial adhesion: in vitro and in vivo evaluation of nisin-treated implantable materials

A novel approach to controlling unwanted microbial adhesion in clinical environments is to inhibit the initial attachment of bacteria, rather than trying to remove them once they have adhered. Previous investigations have established that antimicrobial peptides such as nisin can adsorb to surfaces and still retain sufficient activity to inhibit pathogenic bacteria. We examined techniques of application of nisin in vitro to elucidate those most effective and practical for use on biomedical implants in vivo. Nisin adsorbed quickly on Polyvinyl chloride (PVC) suction catheter tubing, with only a slight gain in nisin activity as contact times increased from 10 s to 8 h. The activity of nisin adsorbed on PVC suction catheter tubing increased as solution concentrations increased from 0.01 to 2.0 mg/ml, and it decreased with aging in protein-free phosphate buffer for 48 h and with drying for up to 2 months. When exposed to three species of Gram-positive bacteria, nisin-treated PVC tubing demonstrated an ability to inhibit bacterial growth, while bacteria grew unchecked on catheter material that was untreated. We then examined the ability of nisin to retain its activity in vivo when placed on implants in blood vessels or the upper airway and whether nisin causes tissue reactions greater than untreated implants placed in sheep and ponies. Freshly prepared nisin was applied to Teflon(R) FEP intravenous catheters and to PVC tracheotomy tubes at the time of placement. using a concentration of 1.0 mg/ml and 10-s contact time. Tissue reactions in response to nisin adsorbed on intravenous catheters or tracheotomy tubes did not occur in sheep or ponies. respectively. Nisin activity was retained for more than 5 h but less than I week on intravenous catheters placed in the jugular veins of sheep, and the veins with short-term catheters showed fewer and less severe histologic abnormalities compared with controls, indicating a possible protective effect on vascular endothelium. Nisin activity was retained on PVC tracheotomy tubes maintained for 1-2 h in ponies, but not on tubes in place for 24 h. As the first preclinical trial of nisin-treated implantable materials. this study represents an important first step for developing the potentially broad use of protein antimicrobial films on implantable medical devices. (C) 2002 Elsevier Science B.V. All rights reserved.