Evaluation of chlorines' impact on biofilms on scratched stainless steel surfaces

Biofilms of a wild type Escherichia coli were grown on 316 stainless steel slides in a nutrient starved medium. The stainless steel surfaces were either polished to a smooth finish or scribed. The scribes consisted of lines and crosses. Biofilm samples were taken after 3, 6, 12, 24 and 48 h of growth. After sampling, the slides were soaked in deionized water or 50 or 200 ppm free chlorine prior to vital staining. Images were captured and the areas of viable and total biofilm were estimated. The individual biofilm patches, circularities, total percentage coverage, and viability percentage coverage were analyzed. The biofilms tended to increase in size between 6 and 24 h. A 3-6 h old biofilm on a polished stainless steel surface detached when 200 ppm sodium hypochlorite was applied. When grown in scribes, the circularity decreased up to 24 h, but thereafter increased. As the film grew older, it detached with or without a sodium hypochlorite treatment from the part of the surface that was polished, but remained in the neighborhood of the scribe. Based on the results, we recommend sanitizing at intervals of less than 12 h for this and similar strains of bacteria and protection of stainless steel surfaces to minimize scratching.