Prevention of Biofilm Formation on Food Contact Surfaces by a Nanoscale Plasma Coating

Introduction: Microbial biofilm formation can lead to great food safety issues in the food industry because, once formed, the cells are more resistant to common sanitizing methods. Low temperature plasma coating technology is a method that can effectively prevent biofilm formation on food contact surfaces.

Purpose: Aim of this study was to investigate and compare the anti-biofilm efficacy of a nanoscale plasma coating of trimethylsilane (TMS) and TMS+O₂ (1:4) on stainless steel (SS) and high density polyethylene (HDPE) against biofilms of important foodborne pathogens.

Methods: SS or HDPE wafers (1 cm × 1 cm) were coated with TMS or TMS+O₂ plasma to an approximate thickness of 30 nm. A 3-5 strain-cocktail each of Listeria monocytogenes, Escherichia coli O157:H7, non O157 Shiga Toxin-producing E. coli (STEC), and Staphylococcus aureus was allowed to form biofilms on the wafer surfaces for 48 h. The biofilms were rinsed with peptone water, followed by ultrasonication to release the cells. The pour-plate method was conducted to determine bacterial counts. Laser confocal scanning and scanning electron microscopy were performed to determine the effects of the plasma coating on the cells.

Results: On SS coated with TMS+O₂, L. monocytogenes numbers dropped from 10⁷ to 10⁵ CFU/wafer. For E. coli O157:H7, the TMS treatment resulted in a 1-log reduction, which was better than the TMS+O₂ treatment. TMS also showed better efficacy than TMS+O₂ on S. aureus (10⁶ to 10⁴ CFU/wafer). However, for STEC, neither plasma coating was effective. On HDPE wafers, TMS and TMS+O₂ worked similarly (1-log reduction for L. monocytogenes and STEC, and 2-log reduction for E. coliO157:H7). 

Significance: Results of this study showed TMS and TMS+O₂ coating on SS surfaces could significantly reduce biofilm formation. However, the efficacy of the treatment depends on the strain, growth conditions, coating surface and material tested.