Measurement of microbial colonisation of two types of stainless steel

The biological colonisation of stainless steel surfaces (AISI 304 resp. 316L) was investigated by monitoring the development of natural biofilms, axenic biofilms with selected laboratory strains, and axenic biofilms with a natural biofilm isolate. Digital image analysis of epifluorescence microscopic photographs for quantification of biofilm formation was applied, me strains producing extracellular polymeric substances (EPS) were faster at colonising of steel surface than a non-EPS producing reference strain. However, by far the most rapid colonisation was achieved by the xenic microbiota present in surface water. A distinct preferential colonisation of grain boundaries of the steel surface was noticeable. This is probably related to minor physical or chemical differences in surface characteristics. These (micro)heterogeneities on the steel surface are considered to be related to subsequent anode/cathode formation or to corrosion of the steel. Finally, the steel grade 304 was slightly more susceptible to colonisation than 316L as observed by digital image analysis, most probably due to the presence of molybdenum in the case of 316L.