Antibacterial Effect of Stainless Steel Surfaces Treated with a Nanotechnological Coating Approved for Food Contact

Abstract

Stainless steel, widely present in the food industry, is frequently exposed to bacterial colonization with possible consequences on consumers' health. 288 stainless steel disks with different roughness (0.25, 0.5 and 1 μm) were challenged with four Gram-negative (Escherichia coli ATCC 25922, Salmonella typhimurium ATCC 1402, Yersinia enterocolitica ATCC 9610 and Pseudomonas aeruginosa ATCC 27588) and four Gram-positive bacteria (Staphylococcus aureus ATCC 6538, Enterococcus faecalis ATCC 29212, Bacillus cereus ATCC 14579 and Listeria monocytogenes NCTT 10888) and underwent three different sanitizing treatments (UVC, alcohol 70% v/v and Gold lotion). Moreover, the same procedure was carried out onto the same surfaces after a nanotechnological surface coating (nanoXHAM^® D). A significant bactericidal effect was exerted by all of the sanitizing treatments against all bacterial strains regardless of roughness and surface coating. The nanoXHAM^® D coating itself induced an overall bactericidal effect as well as in synergy with all sanitizing treatments regardless of roughness. Stainless steel surface roughness is poorly correlated with bacterial adhesion and only sanitizing treatments can exert significant bactericidal effects. Most of sanitizing treatments are toxic and corrosive causing the onset of crevices that are able to facilitate bacterial nesting and growth. This nanotechnological coating can reduce surface adhesion with consequent reduction of bacterial adhesion, nesting, and growth.

Keywords: bactericidal effect; nanoXHAM® D; nanotechnological coating; roughness; stainless steel.

Figure 1

Representative image of stainless steel disks with different roughness, R 0.25, R 0.5, and R 1 μm treated nanoXHAM^® D.

Figure 2

FT-IR spectra (cm⁻¹) of untreated stainless steel disks and treated with nanoXHAM^® D coating.

Figure 3

Graphical representation of the antibacterial activity of UV, alcohol 70% v/v and GL against Gram-positive bacteria (A–D) at different AISI 316 stainless steel surface roughness, **** p < 0.0001, *** p < 0.001, ** p < 0.01, * p < 0.05; Limit of detection (LOD) is 10¹ (10E+1).

Figure 4

Graphical representation of the antibacterial activity of different AISI 316 stainless steel surface roughness against Gram-positive bacteria (A–D); Limit of detection (LOD) is 10¹ (10E+1).

Figure 5

Graphical representation of the antibacterial activity of UV, alcohol 70% v/v and GL against Gram-negative bacteria (A–D) at different AISI 316 stainless steel surface roughness, **** p < 0.0001, *** p < 0.001, ** p < 0.01, * p < 0.05; Limit of detection (LOD) is 10¹ (10E+1).

Figure 6

Graphical representation of the antibacterial activity of different AISI 316 stainless steel surface roughness against Gram-negative bacteria (A–D); Limit of detection (LOD) is 10¹ (10E+1).

Figure 7

Graphical representation of the antibacterial activity of UV, alcohol 70% v/v and GL against Gram-negative bacteria (A–D) at different AISI 316 stainless steel surface roughness coated with nanoXHAM^® D, **** p < 0.0001, ** p < 0.01, * p < 0.05; Limit of detection (LOD) is 10¹ (10E+1).

Figure 8

Graphical representation of the antibacterial activity of different AISI 316 stainless steel surface roughness coated with nanoXHAM^® D against Gram-negative bacteria (A–D), * p < 0.05; Limit of detection (LOD) is 10¹ (10E+1).

Figure 9

Graphical representation of the antibacterial activity of UV, alcohol 70% v/v and GL against Gram-positive bacteria (A–D) at different AISI 316 stainless steel surface roughness coated with nanoXHAM^® D, **** p < 0.0001, ** p < 0.01, * p < 0.05; Limit of detection (LOD) is 10¹ (10E+1).

Figure 10

Graphical representation of the antibacterial activity of different surface roughness on nanoXHAM^® D-treated disks against Gram-positive bacteria (A–D), * p < 0.05; Limit of detection (LOD) is 10¹ (10E+1).

Figure 11

Small range (30 × 30 μm) 3D AFM topographic reconstruction of stainless steel disk surface before (A–C) and after (D–F) nanoXHAM^® D surface treatment. The relative large-scale roughness values (R 0.25, R 0.5 and R 1) are indicated at the bottom of panels. RMS roughness values correspondent to each scan are reported in the top left corner.

Figure 12

Environmental scanning microscopy morphological analysis on a (A) nanoXHAM^® D-treated stainless steel disk surface observed at 300 μm along with its (B) X-EDS microanalysis.