Prevention of Mixed-species Biofilm Formations on Stainless Steel and Plastic Surfaces by a Nanoscale Plasma Coating

Introduction: Mixed-species biofilms are more stable than single species biofilms because cell-to-cell interactions can affect their formation. Cold plasma is a novel non-thermal food processing technology that uses energetic, reactive gases to inactivate contaminating microbes on food and food contact surfaces. Nanoplasma coatings can inhibit initial cell adhesion to surfaces by changing the surface energy and contact angle of the surface. 

Purpose: To investigate the anti-biofilm efficacy of trimethylsilane (TMS) and TMS+oxygen plasma coatings on stainless steel (SS) and high density polyethylene (HDPE) surfaces against complex biofilms.  

Methods: SS and HDPE wafers were coated with TMS and TMS+O₂ plasma. Two groups of mixed-species biofilms: Listeria monocytogenes (LM) and Salmonella enterica (SE), and Escherichia coli O157:H7 (EC) and SE were formed on the wafers for 48 h. The biofilms were removed by rinsing and ultrasonicating each wafer four times for 30 s each time. The pour-plate method was conducted to determine bacterial counts.

Results: On coated SS, the total number of a mixed-species biofilm of LM and SE dropped from 10⁷ (100:1 LM:SE) to 10⁶ CFU for both TMS (8:3 LM:SE) and TMS+O₂ (14:3 LM:SE) treatments. EC and SE mixed-species biofilm was reduced by 70% on TMS plasma-coated (1:60 EC:SE) and 45.56% on TMS+O₂ coated (1:30 LM:SE) SS. The LM and SE mixed biofilm was reduced by 1 log CFU on TMS plasma-coated (100% SE) and by 2 log CFU on TMS+O₂ coated (93.3% SE) HDPE. However, there was no significant reduction in EC and SE mixed-species biofilm cell counts on both TMS and TMS+O₂plasma coated HDPE.   

Significance: This study shows that TMS-coated SS and HDPE surfaces could significantly inhibit some mixed-species biofilms. Further, the bacteria in a mixed biofilm also played a role in the reduction of a single species in the biofilm.