Background Ultraviolet (UV) light irradiation is used in a variety of applications, such as food, air and water purification. The mechanism of UV disinfection differs considerably from chemical disinfectants: UV is mutagenic to bacteria, viruses and other microorganisms by damaging nucleic acids and preventing replication. However, the effectiveness of UV disinfection depends on a number of factors: time of UV exposure; power of the UV source; presence of UV barriers like airborne particles; microorganism resistance.
Purpose To study the effectiveness of UV disinfection inside APOTECAchemo, the robot for preparing antitumour drugs in use at the University Hospital of Ancona. The Killing Rate (KR) and optimal exposure time were determined.
Materials and Methods 5 different microorganisms were chosen for the study in order to cover all the most common families of microbes: Candida albicans; Escherichia coli; Bacillus subtilis; Staphylococcus aureus; Pseudomonas aeruginosa. Different concentrations of each organism (from 107 CFU/ml to 0.5 CFU/ml) were subjected to UV radiation for different exposure times. The plates were located inside the APOTECAchemo compounding room, using the robot’s UV equipment. The KR (logarithmic ratio of the concentration of microorganisms after and before irradiation) was plotted against the exposure time in order to chart the inactivation curves.
Results With a four-hour exposure, the UV irradiation kills all microorganisms at the highest concentrations. The location of the plates inside the system showed only a slight effect on the killing rate, probably thanks to the mirror effect of the stainless steel surfaces. Bacillus subtilis confirmed the strongest UV resistance, indeed 4-hour exposure was necessary to kill 107 CFU/ml. The least resistant microorganism was Escherichia coli, which required 2 hours of UV irradiation.
Conclusions UV radiation is a fundamental step in the sterilisation of workplaces. In fact, 4-hour exposure showed an effective sterilisation (KR < 7) outcome, even for very resistant microorganisms (Bacillus subtilis).
No conflict of interest.
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