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. 2025 Jul 22:16:1570334.
doi: 10.3389/fmicb.2025.1570334. eCollection 2025.

Assessment of the anti-biofilm effect of UV-C irradiation (254 nm) against healthcare associated infections related microorganisms

Francesco Palma  1 , Marta Díaz-Navarro  2   3 , Andrés Visedo  2   3 , Pablo Sanz-Ruíz  3   4   5 , Giorgio Brandi  1 , Giuditta Fiorella Schiavano  6 , María Guembe  2   3
Affiliations

Assessment of the anti-biofilm effect of UV-C irradiation (254 nm) against healthcare associated infections related microorganisms

Francesco Palma et al. Front Microbiol. .

Abstract

Introduction: Biofilm-related Multidrug Resistance (MDR) is a major problem in healthcare-associated infections (HAI). Hospital surface decontamination is essential to ensure the safety of patients and to eliminate the dissemination of MDR pathogens. New eco-friendly decontamination technologies, such as UV-C irradiation, are only gaining popularity now, but their use against the biofilm of common microorganisms causing HAI has not been properly assessed. We aimed to assess the efficacy of UV-C irradiation (254 nm) in a 2-phase study by assessing its anti-biofilm effect against sessile cells from microorganisms of hospital interest.

Methods: The following strains were tested: methicillin-susceptible Staphylococcus aureus (MSSA) (ATCC 29213), methicillin-resistant Staphylococcus aureus (MRSA) (ATCC 43300), Escherichia coli ATCC 25922, Pseudomonas aeruginosa ATCC 15442, and Candida albicans (ATCC 14053), and a clinical strain of methicillin-resistant Staphylococcus epidermidis. First, the tested strains' UV-susceptibility was evaluated through irradiation tests on plates using different UV doses, considering both planktonic and 24 h-biofilm states. Second, the anti-biofilm effect of UV-C was evaluated on stainless steel discs contaminated with a 24 h-biofilm of each strain.

Results: With a UV dose of 946.7 mJ/cm2, the UV-C irradiation on MSSA ATCC 29213, MRSA ATCC 43300, and MRSE biofilm showed a log10 reduction of 4.34 ± 0.70, 4.70 ± 0.60, and 4.85 ± 0.98, respectively, while C. albicans ATCC 14053 showed higher UV-resistance in 24 h-biofilm state, being the log10 reduction of 3.17 ± 0.08. Against Gram negative bacteria biofilm, a UV dose of 467.8 mJ/cm2 was enough to achieve a microbial titer <1 CFU/mL. Regarding the 24 h-biofilm on discs, a log10 reduction >3 logs was achieved with all microorganisms applying a UV dose of 946.7 mJ/cm2.

Conclusion: The application of UV-C irradiation could be a valid additional approach in the management of biofilm HAI.

Keywords: UV-C; biofilm; disinfection; healthcare-associated infection; hospital surface.

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Conflict of interest statement

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Figures

Six bar graphs display the effect of different UV doses (0, 12.8, 37.4, 83.8 mJ/cm2) on CFU/mL values. Each graph shows a decreasing trend in Log10 CFU/mL with increasing UV dose, signifying UV's efficacy in reducing microbial load. Statistical significance is indicated with asterisks above the bars. R-squared values range from 0.7238 to 0.9256 across the graphs.
Figure 1
Log10 microbial load (CFU/mL) of MSSA, MRSA, MRSE, E. coli, P. aeruginosa, and C. albicans strains obtained onto solid medium applying a UV-dose of 0 (control), 12.8, 37.4, and 83.8 mJ/cm2. Bar charts are shown as mean ± standard deviation (SD). Mean values ± SD from three independent experiments (n = 3, for each experimental condition) (3 independent experiments). 2way ANOVA, *p < 0.05; **p < 0.01; ***p < 0.001.
Bar charts demonstrate the effect of increasing UV doses (0, 228.6, 467.8, 946.7 mJ/cm2) on log10 CFU/mL across six different groups. Each chart shows a significant decrease in microbial load with higher UV doses, indicated by asterisks for statistical significance (***). R-squared values range from 0.8772 to 0.995, indicating strong correlations. Error bars represent variability within data.
Figure 2
Survival of MSSA, MRSA, MRSE, E. coli, P. aeruginosa, and C. albicans cells grown in a 24 h-biofilm after exposure to UV-C irradiation applying a UV-dose of 0 (control), 228.6, 467.8, and 946.7 mJ/cm2. The tests were performed on dry biofilm in 96-well cell culture microtiter plates. Bar charts are shown as mean ± standard deviation (SD) from three independent experiments (n = 3, for each experimental condition) (3 independent experiments). 2way ANOVA, ***p < 0.001.
Six bar graphs displaying the effects of varying UV doses (0, 228.6, 467.8, and 946.7 mJ/cm2) on bacterial concentration measured in log10 CFU/mL. All graphs show a decrease in bacterial concentration with increased UV dose, with statistical significance indicated by asterisks. Each graph has a different R-squared value, ranging from 0.85 to 0.9907.
Figure 3
Survival of MSSA, MRSA, MRSE, E. coli, P. aeruginosa, and C. albicans cells grown in a 24h-biofilm on stainless steel discs after exposure to UV-C irradiation applying a UV-dose of 0 (control), 228.6, 467.8, and 946.7 mJ/cm2 on each disc side. Bar charts are shown as mean ± standard deviation (SD) from three independent experiments (n = 3, for each experimental condition) (3 independent experiments). 2way ANOVA, **p < 0.01; ***p < 0.001.
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