Interactions between Staphylococcus epidermidis,monocytes and nano structured gold surfaces

Abstract

Master thesis, Programme in Medicine. TITLE: Interactions between Staphylococcus epidermidis, monocytes and nano structured gold Surfaces. AUTHOR: Magnus Forsberg. The role of material surface properties for the direct interaction with bacteria and the indirect route via host defense cells is not fully understood. Recently, nanostructured implant surfaces were suggested to possess antimicrobial properties. In the present study the adhesion and biofilm formation of Staphylococcus epidermidis and human monocyte adhesion and activation were studied separately and in co-culture in different in vitro models by using smooth (Au) and well defined nanostructured (AuNP) gold model surfaces. Two polystyrene surfaces were used as controls in the monocyte experiments. Fluorescent viability staining demonstrated a reduced viability of S. epidermidis close to the nanostructured surface, while the smooth Au correlated with more live biofilm. The results were supported by scanning electron microscopy observations, showing higher biofilm tower formations and more mature biofilms on Au compared to AuNP. Unstimulated monocytes on the different substrates demonstrated low activation as measured by chemiluminescence, gene expression of pro- and anti-inflammatory cytokines and cytokine secretion. In contrast, stimulation with opsonized zymosan or opsonized live S. epidermidis during 1 h, significantly increased the production of reactive oxygen species, the gene expression of tumor necrosis factor-alpha (TNF-α), interleukin-1beta (IL-1β), IL-6 and IL-10 and the secretion of TNF-α, demonstrating the ability of the cells to elicit a response and actively phagocytise the preys when present on all surfaces. In addition, cells on the smooth Au and AuNP showed a different adhesion pattern and a more rapid oxidative burst than on polystyrene upon stimulation. It is concluded that S. epidermidis decreased its viability initially when adhering to nanostructured compared to smooth gold surfaces, especially in the bacterial cell layers closest to the surface. On the other hand, material surface properties neither strongly promoted nor attenuated the activity of monocytes when exposed to zymosan particles or S. epidermidis. Keywords: nanotopography, staphylococci, host defense, bacteria, zymosan, macrophage