Far-UV-C radiation demonstrated germicidal activity against Escherichia coli and Staphylococcus sp.

Abstract

Background: Bacteria are ubiquitous microorganisms with economic and public health impacts [1, 2]. Proper disinfection of public spaces minimizes bacterial contamination, spread, and associated diseases [3, 4]. Ultraviolet radiation (UV) is an effective and inexpensive approach for bacterial control and eradication [5-7]. Objective: This study aimed to evaluate the bactericidal potential of far-UV-C (222 nm) – an irradiation technology requiring scientific validation. Methods: The bactericidal effect of far-UV-C (from 104.6 μW/cm² to 918.0 μW/cm²; 222 nm; 1 and 5 min), against adhered cells of Escherichia coli and Staphylococcus sp., was determined. Ultrasounds (for 1 min), as well as sodium hypochlorite, N-alkyl-N,N-dimethyl-N-benzyl-ammonium chloride, pentapotassium bis (peroxymonosulfate) bis(sulfate)), and perillyl alcohol (at sub-bactericidal concentrations for 5 min) were also tested. In addition, irradiation was combined with ultrasounds and each of the four compounds. Finally, the effect of the treatment UV + ultrasound + free chlorine was assessed. The effectiveness of each treatment was evaluated through the calculation of the percentage of reduction. Results: For 1 min of exposure to UV-C, percentages of reduction were between 42% and 94% for E. coli, while for Staphylococcus sp. these percentages ranged from 30% to 91%. For 5 min of exposure to radiation, percentages of reduction were from 79% to 100% for E. coli and were between 51% and 99% for Staphylococcus sp. Interestingly, the combinations were successful: UV + ultrasound showed synergism and the combinations of UV with each compound resulted in percentages of reduction equal to 100% for E. coli and higher than 96% for Staphylococcus sp. The triple combination resulted in a percentage of reduction of 100% for both bacteria. Conclusions: Far-UV-C reduces microbial contaminations successfully. In particular, combinatorial approaches were more effective than individual treatments, making these treatments adequate for disinfecting public spaces.