Comparison of plastic biliary prosthesis with and without application of silver nanoparticles: in vitro study of intraluminal biofilm formation

Abstract

The endoscopic or percutaneous insertion of biliary prostheses has been used since the 1970s with the aim of effecting drainage in malignant obstructive diseases of the biliary tract, as well as in benign strictures. However, the duration of patency of this prosthesis is limited by progressive obstruction of its lumen. This is considered a major complication of biliary prostheses, occurring in a significant number of cases (10-30%) and is associated with recurrent jaundice with or without cholangitis, necessitating removal and replacement of new prosthesis, which results in increased levels of morbidity and additional costs for the health system. Several factors are involved in biliary stent occlusion such as the formation of adherent bacterial biofilms in its lumen. Thus, various strategies have been proposed in order to eliminate it, intending to postpone the period of occlusion of the prosthesis and decrease the risk of infection of the biliary tract. Technological advances that allowed the reduction of silver to the nanoparticle scale and integration of its valuable antimicrobial activity in a larger number of materials have opened up a new perspective for the production of biliary prostheses since silver is known for its antimicrobial properties . Thus the aim of this study is to analyze the effects of silver nanoparticles applied in biliary prosthetics on biofilm formation, with the aim of preventing or delaying their obstruction and, consequently, the infection of the biliary tract, as well as product development and in vitro tests realization. Plastic biliary prostheses with and without modification of their surfaces with the use of silver nanoparticles are to be compared. The culture media to be used will be specific for each bacterium tested and enriched with animal bile (pig). Bile will be obtained by sterile puncture of the gallbladder of pigs from the bacterium (which will undergo surgical procedures of the biliary tract, involving cholecystectomy in the laboratory of Surgical Technique and Experimental Surgery, University of São Paulo). There will be used strains of organisms that are required to be tested for quality control tests (National Committee for Clinical Laboratory Standards (NCCLS), provided by ATCC - American Type Culture Collection: Enterococcus faecalis ATCC ® 29212, Escherichia coli ATCC ® 25922 , Escherichia coli ATCC ® 35218, Pseudomonas aeruginosa ATCC ® 27853, Staphylococcus aureus ATCC ® 25923, Staphylococcus aureus ATCC ® 43300. Then, new segments of prostheses, with and without silver nanoparticles, previously sterilized, will be assembled in a closed container and bathed with the animal bile, infected with E. coli and/or Enterococcus, for 7 days. Each day, 3 segments of prostheses and bile samples will be removed and microbiologically evaluated to determine the planktonic (nonadherent) bacterial count and assess microbial adherence. For this purpose, the segments of prostheses removed will be rinsed in sterile saline to remove free bacteria (planktonic) and then scraped with a sterile blade. The scraped material and the prostheses segments will be suspended in sterile saline and centrifuged at low speed for 5 minutes. An aliquot of this solution will be taken for microbiological analysis and colony counting. Prostheses segments will be evaluated by electron microscopy scanning, with photographs of the images, to confirm the presence of bacterial adhesion and biofilm formation. Technical and anatomopathological individualized variables will be analyzed as isolated predictors and comparing each group among themselves. The variance and statistical significance will be presented in absolute reason. All data will be stored in SPSS system.(AU)