Effect of wax chain length on the adhesion dynamics and interfacial rigidity of Salmonella Typhimurium LT2

The wax layer on the surface of fruits and vegetables is the first line of defense against a range of environmental stresses. The initial stage in the etiology of bacterial foodborne illnesses involves the bacterial adhesion and colonization on the wax layer of food commodities. Herein, we report a systematic study that provides new insights into dynamics of interfacial nanoscale processes associated with the transition of bacteria from a planktonic state to a sessile state at the early stages. To achieve this, we coated a piezoelectric sensor with model waxes containing linear alkyl carbon chains of varying lengths (from 6 to 18 carbons) via chemisorption. The process of bacterial adhesion to these wax-coated sensors was monitored using the Quartz Crystal Microbalance with Dissipation (QCM-D) technique, which offers nanogram-level gravimetric accuracy and millisecond time resolution. Our findings revealed that surfaces with higher hydrophobicity are more susceptible to Salmonella adhesion. Furthermore, we conduct a comparative analysis of the viscoelastic properties of the adhered layer, revealing distinct behaviors: Salmonella adhered to C6-wax exhibited solid-like characteristics, while adherence to C18-wax rendered a more liquid-like response. This observation underscores the role of interfacial energy in governing bacterial adhesion, as interpreted through the thermodynamic and surface science model, ultimately influencing rigidity. This investigation offers valuable insights into the initial adhesion to surfaces and has potential implications for surface design and modification within the food industry and other relevant applications, while also contributing to our understanding of bacterial contamination in food commodities.