Determining the rate of deactivation of staphylococcus aureus and escherichia coli by ultraviolet light

Abstract

Ultraviolet C light is commonly used as an effective decontaminant in the laboratory, healthcare, and industrial settings. However, one major limitation of Ultraviolet C light is the ability of some microorganisms such as bacteria to efficiently repair their DNA after Ultraviolet C treatment. The bacteria repair their DNA through mechanisms known as photoreactivation and dark repair. This poses a potential risk of bacterial re-emergence, contamination, and infection after Ultraviolet C treatment. To address this problem, the rate of deactivation of the bacteria Staphylococcus aureus and Escherichia coli by Ultraviolet C light and the minimum exposure time required for their complete deactivation were determined. The bacteria were plated on selective and differential media and exposed to Ultraviolet C light at different durations of time in increments of five minutes. The plates were then incubated for a period of 24 hours and the number of bacteria colonies formed thereafter were counted. This was done until the exposure time that corresponded with no bacteria colony formation was reached. The number of bacteria colonies counted were used to calculate the overall rate of deactivation of Staphylococcus aureus which was 6 %min-1 of Ultraviolet C exposure and that of Escherichia coli which was 8 %min-1 of Ultraviolet C exposure. These deactivation rates can be used to calculate the killing capacity of Ultraviolet C at any duration of exposure to the bacteria. This is essential in achieving a particular decontamination goal in any setting where Ultraviolet light is used as a decontaminant.