Attachment of Salmonella spp. and Listeria monocytogenes to stainless steel, rubber and polytetrafluorethylene: the influence of free energy and the effect of commercial sanitizers

Abstract

Bacteria and material surfaces were characterized with respect to their hydrophobicity and surface free energy using the contact angle method. Salmonella strains showed higher hydrophobicity and lower surface free energies than Listeria monocytogenes strains. Polytetrafluorethylene was the most hydrophobic material (and had the lowest surface free energy), followed by rubber and stainless steel. Bacteria attached in higher numbers to the more hydrophobic materials. Bacterial adherence could not be correlated with surface free energies or contact angles of bacteria, although L. monocytogenes strains attached in higher numbers than Salmonella strains to all of the materials tested. The cleaning of materials with commercial sanitizers resulted in a decrease of their contact angles (and an increase of their surface free energies), accompanied by a reduction in the number of adhered bacteria in comparison with the standard conditions. The degree of reduction in bacterial adherence varied with the bacteria, the substrate material and the sanitizer tested. Quaternary ammonium compounds were more effective against Salmonella attachment than L. monocytogenes attachment. Diethylenetriamine showed similar efficacy against attachment of both bacteria. Polytetrafluorethylene showed the greatest reduction in attachment after being washed with commercial sanitizers. It is concluded that stainless steel is less adherent than rubber or polytetrafluorethylene and should be preferred in the food industry when possible. On the other hand, polytetrafluorethylene seems to be more easily sanitized. Since effectiveness of sanitizers in the reduction of bacterial adherence was dependent upon the bacteria and the materials studied, the use of mixtures of sanitizers would help to control bacterial adherence in the food industry.