Measurement of microbial colonisation of two types of stainless steel

The biological colonisation of stainless steel surfaces (AISI 304 resp. 316 L) was investigated by monitoring the development of natural biofilms, axen ic biofilms with selected laboratory strains, and axenic biofilms with a na tural biofilm isolate. Digital image analysis of epifluorescence microscopi c photographs for quantification of biofilm formation was applied, me strai ns producing extracellular polymeric substances (EPS) were faster at coloni sing of steel surface than a non-EPS producing reference strain. However, b y far the most rapid colonisation was achieved by the xenic microbiota pres ent in surface water. A distinct preferential colonisation of grain boundar ies of the steel surface was noticeable. This is probably related to minor physical or chemical differences in surface characteristics. These (micro)h eterogeneities on the steel surface are considered to be related to subsequ ent anode/cathode formation or to corrosion of the steel. Finally, the stee l grade 304 was slightly more susceptible to colonisation than 316L as obse rved by digital image analysis, most probably due to the presence of molybd enum in the case of 316L.