Diamond like carbon Ag nanocomposites as a control measure against Campylobacter jejuni and Listeria monocytogenes on food preparation surfaces

Abstract

The effect of thin (5nm) and thick (40nm) silver layers and diamond like carbon nanocomposites with embedded Ag nanoparticles (DLC:Ag) against two reference strains of C. jejuni NCTC 11168 and L. monocytogenes ATCC 7644 were evaluated in this study. DLC:Ag film contained 22at.% Ag. Silver nanoparticle size measured by transmission electron microscope was in the 5–10nm range. Ag layers and DLC:Ag nanocomposites were deposited employing unbalanced reactive magnetron sputtering on crystalline silicon wafers. C. jejuni and L. monocytogenes numbers were counted by culture-based enumeration on selective agars and quantitative real-time PCR (qPCR) including staining with propidium monoazide (PMA). It was determined, that DLC:Ag film was the most efficient coating in the reduction of C. jejuni and L. monocytogenes numbers. Culture-based enumeration revealed that C. jejuni numbers were reduced by an average of 4.06log10CFU/ml after 15min and 3.61log10CFU/ml after 30min on DLC:Ag coated silicon wafers in comparison to control samples (P≤0.05). L. monocytogenes was not detected on DLC:Ag samples after 24h of exposure (P≤0.05). PMA-qPCR showed that C. jejuni and L. monocytogenes affected by DLC:Ag antimicrobial surface showed a reduced ability to grow on culture media, but maintained viability during the whole experiment. Nonetheless, DLC:Ag antimicrobial surface could be further considered for the reduction of cross-contamination risk from food preparation surfaces due to their contamination with C. jejuni and L. monocytogenes in domestic and commercial kitchens or food establishments.