Biofilm impact on the stainless steel passive film

摘要

For micro-organisms, the preferred living state is adhering to surfaces that lead to the development of a biofilm. It is well known that the material chemical composition and its topography affect microbial colonization . Furthermore, adhesion to surfaces and growing inside biofilm modify microbial metabolism . The secreted products by adhering cells will modify their local environment in terms of pH, RedOx. Thus, biofilm can affect surface properties of materials.In aqueous environment, materials are mainly chosen for their corrosion resistance property. For stainless steels, the corrosion resistance is due to the formation of a thin passive chromium and iron oxide/hydroxide . The passive film modification in presence of bacteria is a key issue for the integrity and reliability of metallic materials. The purpose of the present work is to study the modifications of the passive film on stainless steel after initial adhesion of E. coli K12 (1h) and in the early stage of biofilm formation (24h).Observations performed by TEM (Transmission Electronic Microscopy) confirmed the presence of the passive layer under the bacterial cells. XPS (X-Ray Photoelectron Spectroscopy) was used to define chemical composition of the passive layer near and under E. coli cells. The E. coli cells were removed by sputtering to define the oxide layer composition under bacteria. The work evidence that the passive film formed after E. coli adhesion is enriched in Cr compared to the passive film not exposed to bacteria. The enrichment in Cr is observed in the oxide film under bacteria as well as in the oxide film not covered by bacteria (next to the bacteria). The longer the exposure time, the richer in chromium is the passive film.