In vitro Salmonella typhi biofilm formation on gallstones and its disruption by Manuka honey

Abstract

Biofilm is a complex community of single or different types of microorganisms (bacteria, viruses, fungi, protozoa) attached to a surface and stick to each other through production of extracellular matrix. Salmonella typhi forms biofilm on cholesterol gallstones resulting in carrier state. Once formed, biofilm is difficult to treat. To date cholecystectomy is the only cure for this condition. Manuka honey is known to have tremendous antibiofilm activity against various organisms. S. typhi biofilm was grown in vitro on clinical samples of human cholesterol gallstones by Gallstone tube assay method for 12 days. Biofilm mass was quantified on day 1, 5, 7, 9 and 12 by crystal violet assay and was also examined by scanning electron microscope. Three concentrations w/v of Manuka honey (40%, 60% and 80%) were used, each one at 24, 48 and 72 hours. The most effective concentration (80% w/v) was repeated on two sets of gallstones. Biofilm mass was re quantified by crystal violet assay and was examined by scanning electron microscope. S. typhi formed uniform biofilm on cholesterol gallstone surface. The optical density measurements exhibited a rising pattern with time thereby indicating an increase in biofilm mass. It was 0.2 on day 1 and 0.9 on day 12. With 80% w/v Manuka honey, biofilm mass decreased most effectively with 0.5 OD after 72 hours. Biofilm formation by S, typhi on gallstones is surface specific and bile dependant. Either increasing the duration (beyond 72 hours) of the effective concentration (80% w/v) of honey or increasing the concentration (above 80%) of honey for a specific duration (72 hour) may cause complete disruption of the S. typhi biofilm on gallstone. S. typhi forms biofilm on cholesterol gallstones surface in vitro and it can be visualized by scanning electron microscopy. Biofilm mass can be quantified using crystal violet assay. Among various concentrations 80% Manuka honey for 72 hours is most effective in disrupting S. typhi biofilm on gallstones in vitro as evident from crystal violet assay.