Influence of free energy on the attachment of Salmonella Enteritidis and Listeria monocytogenes on stainless steels AISI 304 and AISI 316

Abstract

Bacterial attachment to stainless steels AISI (American Iron and Steel Institute) 304 and 316, the preferred material choices for food equipment, is a very important food safety consideration. The purpose of the present study was to investigate the attachment of two important food pathogens on commercial samples of these surfaces focusing on the influence of material topography characterized by Atomic Force Microscopy and considering the hydrophobicity and free energy of interaction, determined by measuring contact angle and application of thermodynamic theory principles. Results showed that S. Enteritidis and Listeria monocytogenes were able to attach to samples of stainless steels, however, initially (t = 0), the number of adhered S. Enteritidis (2.55 log CFU/cm^2) was higher than L. monocytogenes (1.68 logCFU/cm^2). Corroborating these results, the adhesion was thermodynamically more favorable for S. Enteritidis. Even though, the number of adhered cells were similar on both stainless steels samples, negative total energy was higher on AISI 316, for both bacteria. Moreover, the surface's roughness (0.032 μm and 0.021 μm) and hydrophobicity of cells and materials did not show a positive correlation with bacterial adherence.