The efficacy of vacuum-ultraviolet light disinfection of some common environmental pathogens

Abstract

Background: This study is to elucidate the disinfection effect of ozone producing low-pressure Hg vapor lamps against human pathogens. Ozone producing low-pressure Hg vapor lamps emit mainly 254 nm ultraviolet light C (UVC) with about 10% power of Vacuum-ultraviolet (VUV) light at 185 nm. The combination of UVC and VUV can inactivate airborne pathogens by disrupting the genetic materials or generation of reactive oxygen species, respectively. In this study, inactivation of common bacteria including Escherichia coli ATCC25922 (E. coli), Extended Spectrum Beta-Lactamase-producing E. coli (ESBL), Methicillin-resistant Staphylococcus aureus (MRSA) and Mycobacterium tuberculosis (MTB), and that of influenza A viruses H1N1 and H3N2 under the radiation from ozone producing low-pressure Hg vapor lamps was examined. Log reduction values at different treatment durations were determined.

Methods: In vitro tests were carried out. Various bacterium and virus suspensions were added onto nitrocellulose filter papers and subjected to the illumination from ozone producing low-pressure Hg vapor lamps. The extents of pathogen inactivation at different illumination times were investigated by conducting a series of experiments with increasing duration of illumination. log10 reduction in CFU/ml and reduction at log10(TCID₅₀) were respectively measured for bacteria and viruses. The disinfection effectiveness of this type of lamps against the pathogens under the environment with a moderate barrier to light was therefore evaluated.

Results: Ozone producing low-pressure Hg vapor lamp successfully inactivated these human pathogens. Nevertheless, among these pathogens, disinfection of MTB required more intense treatment. In the best tested situation, 3-log10 inactivation of pathogens can be achieved with ≤10 min of VUV treatment except MTB which needed about 20 min. This demonstrated the high resistance against UV disinfection of MTB.

Conclusions: Following the criteria that valid germicidal results can be reflected with 3-log10 inactivation for bacteria, 4-log10 inactivation for viruses and 5-log10 inactivation for MTB, most of the bacteria required ≤10 min of VUV treatment, 20 min for the influenza viruses while MTB needed about 30 min VUV treatment. This indicated that VUV light is an effective approach against different environmental microorganisms.

Keywords: Disinfection; ESBL; IAQ; Influenza; MRSA; Microorganism; Ozone; Tuberculosis; VUV.

Fig. 1

The VUV illumination experiment

Fig. 2

VUV light disinfection against E. coli, ESBL and MRSA. Both 10-fold (a) and 100-fold (b) diluted 0.5 McFarland standard inoculums of E. coli (denoted by E. coli with the dilution ratio behind), ESBL (denoted by ESBL with the dilution ratio behind) and MRSA (denoted by MRSA with the dilution ratio behind) were subjected to VUV light disinfection. The log10 (CFU/mL reduction) were plotted against the time of disinfection. Data were plotted as the means of triplicate biological replicates ±error

Fig. 3

VUV light disinfection against MTB. The experimental sets were conducted on 0.5 McFarland standard inoculum (denoted by MTB 1) and 10-fold diluted 0.5 McFarland standard inoculum (denoted by MTB 10). The log10 (CFU/mL reduction) were plotted against the time of disinfection. Data were plotted as the means of triplicate biological replicates ±error

Fig. 4

VUV light disinfection against H1N1 and H3N2 influenza A viruses. The log10 (TCID₅₀/mL reduction) was plotted against disinfection time