Impact of cleaning and disinfection agents on biofilm structure and on microbial transfer to a solid model food

Aim: To determine how single cells and microcolonies transfer to food from open surfaces in the meat industry. Methods and Results: Biofilms of four bacterial strains isolated from food processing surfaces were established on stainless steel substrates conditioned with meat exudate in the presence or absence of CaCl2. Image analysis of the biofilms showed that the addition of calcium resulted in an increase of the number and size of microcolonies with two strains: Staphylococcus sciuri and Pseudomonas fluorescens. Image analysis of the biofilms of those two strains grown in the presence of calcium was performed before and after contacts with tryptone soya agar as a solid model food. For the biofilms treated or not with a chlorinated alkaline agent, where a decrease in surface coverage occurred, it was accompanied by a decrease in the percentage of the coverage accounted for by microcolonies (P-m). Attachment strength was greater for P. fluorescens than for S. sciuri. When the P. fluorescens biofilms were treated with a solution containing glutaraldehyde, the contacts did not modify their structure. By contrast, their treatment with chlorinated alkaline resulted, after contacts, in the smallest coverage and P-m. With S. sciuri, a decrease in coverage after contacts always occurred and was the greatest for the untreated biofilms. Conclusions: After contacts between biofilms and a solid model food, microcolonies were preferentially detached compared with single cells. A chlorinated alkaline product either decreased biofilm attachment strength (P. fluorescens) or unexpectedly increased it (S. sciuri), whereas a glutaraldehyde-based disinfectant increased both attachment strength and microcolony cohesion. Significance and Impact of the Study: The contaminating potential of a surface depends not only on the level of contamination but also on the nature, structure and history of the contamination.