Bacterial composition of refrigerators in households and inactivation of airborne Staphylococcus aureus using a TiO2-UVLED module in a 512 L aerobiology chamber

Abstract

This study aimed to investigate the microbiota in the air and on the surface of a refrigerator and to inactivate aerosolized Staphylococcus aureus using a TiO2-UVLED module. A total of 100 L of the air and 5000 cm2 surfaces in seven household refrigerators were collected using an air sampler and a swab, respectively. Samples were subjected to microbiota analysis as well as quantitative analyses of aerobic or anaerobic bacteria. The level of airborne aerobic bacteria was 4.26 log CFU/vol (100 L), while that of surface aerobic bacteria was 5.27 log CFU/surface (5000 cm2). PCoA based on the Bray-Curtis metric revealed that the bacterial composition differed between samples collected from refrigerators with and without a vegetable drawer. Moreover, pathogenic bacteria containing genera and order from each sample were found, such as Enterobacaterales, Pseudomonas, Staphylococcus, Listeria, and Bacillus. Among them, Staphylococcus aureus was determined to be a core hazardous pathogen in air. Therefore, three S. aureus strains isolated from the air in refrigerators, as well as a reference strain of S. aureus (ATCC 6538P), were inactivated by a TiO2-UVLED module in a 512 L aerobiology chamber. All aerosolized S. aureus were reduced over 1.6 log CFU/vol after treatment with TiO2 under UVA (365 nm) light at 40 J/cm2. These findings suggest that TiO2-UVLED modules have the potential to be used to control airborne bacteria in household refrigerators.