Development of Antimicrobial Surface-modified Stainless Steel with N-halamines: Characterization and Effectiveness against Listeria monocytogenes

Introduction: Cross-contamination of pathogenic bacteria from contaminated food processing surfaces poses a significant risk to food safety. Stainless steel is commonly used to fabricate food processing equipment and has been shown to harbor pathogens like Listeria monocytogenes. Development of antimicrobial stainless steel in which bulk material properties are retained and the antimicrobial activity is long-lasting can support current cleaning and sanitization efforts to improve food safety. N-halamines represent a unique class of antimicrobials capable of recharging their antimicrobial activity with each exposure to halogen-based sanitizers.

Purpose: The purpose of this study was to modify the surface of stainless steel to possess rechargeably antimicrobial N-halamines, to characterize the changes in surface chemistry and finally to evaluate the antimicrobial activity of the modified steel against Listeria monocytogenes.

Methods: Surface modification of stainless steel was performed via layer-by-layer deposition of N-halamine containing polymers and different types of analysis were employed to confirm its chemical modification: FTIR, ellipsometry, X-ray photoelectron spectroscopy, acid orange 7 assay and contact angle. Antimicrobial activity against Listeria monocytogenes was performed by submersion of control and modified steel in bacterial suspensions under varying conditions.

Results: The reported layer-by-layer surface modification technique effectively introduced antimicrobial N-halamines to stainless steel.  Primary amines increased significantly with each N-halamine multilayer. At six multilayers, the stainless steel presented 36.8 ± 6 nmol/cm² of antimicrobial N-halamines. A single multilayer of polymers added onto the surface had a thickness of only 2.0 ± 0.2 nm. The effectiveness against Listeria monocytogenes was demonstrated, in which N-halamine modified steel was able to inactivate 5 – 6 log CFU/ml in less than 1 h.

Significance: Results indicate that our N-halamine modified stainless steel effectively inactivates Listeria monocytogenes and may therefore represent a means to control the cross-contamination of pathogens from food processing surfaces, reducing the risks of foodborne illness.