The fate of the protective oxide film on stainless steel upon early stage growth of a biofilm

For metals and alloys that are protected against corrosion by a surface oxide film (the passive film), the modification or degradation of this passive film in presence of bacteria is a key issue in terms of integrity and reliability of structures. The objective of this work was to reveal the nature of the interaction of stainless steel with bacteria, in particular the modifications of the passive film after bacteria adhesion in the early stage of biofilm formation. An innovative approach, based on advanced surface analysis, has been developed. The use of Time of Flight Secondary Ions Mass Spectrometry (ToF-SIMS) allowed us to have access to and characterize the bacteria/substrate interface.Here we show that a passive film remains under the bacteria, but its chemical composition is modified. The passive film under Escherichiacoli bacteria, for a surface coverage by bacteria of ∼20%, is enriched in Cr compared to the passive film on stainless steel not exposed to the bacteria.