Effectiveness of Ultraviolet C Decontamination: Identifying Optimal Exposure Times for Reducing Common Hospital Bacterial Strains

Introduction
To prevent white rooms from contaminants, ultraviolet C (UV-C) light is a promising technology in decontaminating material entering into white rooms. A study was conducted to show bacterial decay per unit of time and determine the necessary cycle time for effective decontamination on selected microorganisms.

Material and methods
Three bacterial-reference strains used (Staphylococcus aureus (S.A.) NCTC 10788, Pseudomonas aeruginosa (P.A.) NCTC 12924, and Escherichia coli (E.Coli) NCTC 12923) were tested. For each one, beads (Bioball^® Biomerieux France) were rehydrated, then cultured to obtain concentration around 6.108 CFU/mL. A volume of 0.5 mL of each suspension were dropped on TSA plates. Plates (n=3) were then exposed to UV-C light for different times (1, 2, 3, 4, and 5 minutes) in a UV-C box (Byola Artemeisa^® B300, Byola France). Agar plates were then incubated at 32°C for 48h and bacteria were numbered at 24h and 48h.

Results
24h post-exposure,
For E.Coli on average, 3 UFC were observed on plates exposed to 1 minute of UV-C light. None were observed for the other periods.
For S.A. on average, 1 UFC was observed on plates exposed to 1 minute of UV-C light. None were observed for the other periods.
For P.A. on average, 0 UFC were observed on plates exposed to 1 minutes of UV-C light. None were observed for the other periods.

Conclusions/Discussion
A log 8 reduction is observed after 1 min for E coli, S.A and P.A. Thus, a one-minute cycle time is efficient to reach our goal.
Further perspectives should be performed such as the study of a yeast (Candida albicans) and a spore-forming bacterium (Bacillus).

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