Effect of Selected Environmental Factors on the Microbicidal Effectiveness of Radiant Catalytic Ionization.

Maria Kowalska,Krzysztof Skowron,Zbigniew Paluszak,Jakub Korkus,Katarzyna Kosek-Paszkowska,Joanna Kwiecińska-Piróg,Natalia Wiktorczyk,Katarzyna Grudlewska,Eugenia Gospodarek-Komkowska,Ewa Wałecka-Zacharska,Klaudia Brożek

doi:10.3389/fmicb.2019.03057

Abstract

The aim of this study was the assessment of the effect of time exposure, temperature, distance, and organic contaminants on radiant catalytic ionization (RCI) microbicidal effectiveness. The number of all examined bacteria decreased together with time exposure of RCI. The lowest recovery was obtained, both from the rubber surface (6.36 log CFU × cm–2) and steel (6.04 log CFU × cm–2) in the case of Escherichia coli O157:H7. On the other hand, Staphylococcus aureus was isolated in the largest number (rubber: 7.88 log CFU × cm–2, steel: 7.79 log CFU × cm–2). Among the tested environmental conditions, the greatest bacterial population was re-isolated at 4°C (distance: 0.5 m, time: 24 h), whereas the lowest population was found at a distance of 0.5 m (temperature: 20°C, time: 24 h) and on surfaces without contamination. In the samples treated with RCI, the bacterial population was the lowest on non-contaminated surfaces, ranging from 3.76 log CFU × cm–2 (E. coli O157:H7) to 5.58 log CFU × cm–2 (S. aureus) for the rubber, and from 3.26 log CFU × cm–2 (E. coli O157:H7) to 5.20 log CFU × cm–2 (S. aureus) for the stainless steel. The highest bacteria number was isolated from surfaces contaminated with meat and fish pulp. The lowest bacterial reduction caused by RCI was found in the case of rubber contaminated with meat-fish pulp (24 h, 0.5 m, 20°C). The reduction rate was equal to 0.89 log CFU × cm–2 for S. aureus, 1.17 log CFU × cm–2 for Listeria monocytogenes, 1.43 log CFU × cm–2 for Salmonella Enteritidis and 1.61 log CFU × cm–2 for E. coli O157:H7. In turn, the greatest bacterial reduction was found in the case of non-contaminated steel (24 h, 0.5 m, 37°C). The reduction rate was equal to 4.52 log CFU × cm–2 for L. monocytogenes, 3.61 log CFU × cm–2 for S. Enteritidis, 2.98 log CFU × cm–2 for E. coli O157:H7 and 2.77 log CFU × cm–2 for S. aureus. RCI allows the inactivation of pathogens from stainless steel and rubber surfaces. Its efficacy is species-dependent and affected by environmental factors.

Highlights

Over recent years, a high degree of final product contamination with pathogenic bacteria e.g., Listeria spp., Salmonella spp., Campylobacter spp., Escherichia spp. has been reported in the food industry (Kathariou, 2002; European Food Safety Authority [EFSA], 2017)
The aim of this study was the assessment of Radiant Catalytic Ionization (RCI) efficacy as a disinfection method against selected pathogens (Listeria monocytogenes ATCC R 19111TM, Escherichia coli O157:H7 ATCC R 43895TM, Staphylococcus aureus ATCC R 29213TM, Salmonella Enteritidis ATCC R 13076TM) on stainless steel and rubber
We demonstrated that RCI eradicated planktonic cells and biofilm of L. monocytogenes from food contact surfaces i.e., stainless steel, earthenware, rubber, and polypropylene

Summary

Introduction

A high degree of final product contamination with pathogenic bacteria e.g., Listeria spp., Salmonella spp., Campylobacter spp., Escherichia spp. has been reported in the food industry (Kathariou, 2002; European Food Safety Authority [EFSA], 2017). One of the main reasons behind food products contamination in food plants is bacterial biofilm on the foodprocessing surfaces (tanks, tapes, cutting elements), ceilings, and walls of production halls (Pan et al, 2006; Swaminathan and Gerner-Smidt, 2007). Such biofilms are difficult to eliminate and pose a risk to consumer health. In the case of RCI cells, we deal with TiO2 nanotubes generated in the hydrothermal reaction of titanium oxide with NaOH at 180◦C (Llorensa et al, 2012). A schematic diagram of the chain oxidation reaction is shown below (Chong et al, 2010):

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