Interaction between natural microbiota and physicochemical characteristics of lettuce surfaces can influence the attachment of Salmonella Enteritidis

Adhesion of Salmonella Enteritidis to lettuce leaves cultivated in hydroponic or conventional systems was evaluated in the context of competitive microflora and physicochemical characteristics of leaves. A thermodynamic study based on the determination of the total free energy of surface interactions was conducted to predict pathogen leaf adhesion. A higher number of S. Enteritidis adhered to the lettuce leaves cultivated in a hydroponic system (p < 0.05). In addition, roughness values indicated that lettuce cultivars grown hydroponically exhibited more wrinkly surfaces (p < 0.05). Lettuce leaves that were cultivated in a conventional system and S. Enteritidis surfaces were classified as hydrophilic because of positive free energy values ( Δ G sws > 0 ). Lettuce cultivated in a hydroponic system presented a negative (hydrophobic) free energy value ( Δ G sws < 0 ). Adhesion of S. Enteritidis to lettuce surfaces was thermodynamically unfavourable, independent of the cultivation method ( Δ G adhesion > 0 ). Thus, the thermodynamic evaluation explains the low number of S. Enteritidis cells that adhered to the lettuce leaves. There was a relationship between the number of S. Enteritidis adhering to the lettuce leaves and the physicochemical characteristics of the microbial and vegetable surfaces. Higher numbers of endogenous microorganisms found in the lettuce leaves from conventional system reduced S. Enteritidis adhesion. The study of the factors involved in bacterial adhesion to food surfaces is of great importance for contamination control and safe food maintenance.