Irradiation with Ultraviolet-C Light-Emitting Diodes: Evaluation of the potential and limitations in controlling the spread of mobile genetic elements

Background: Recent reports of multispecies outbreaks show that, in addition to multidrug-resistant bacteria, the accumulation and spread of antibiotic resistance-conferring genes (ARGs) in clinical settings is a growing concern. Ultraviolet-C (UV-C) technology is an effective method for inactivating microorganisms. This study aims to investigate whether it also offers a potential method to inactivate mobile genetic elements that confer antibiotic resistance by examining the effects of UV-C irradiation on plasmid-encoded resistance genes, focusing on DNA degradation and whether sublethal doses impact bacterial competence. Method: We examined the effects of UV-C on the plasmids pCR™-Blunt II-TOPO and pUC19, focusing on DNA integrity and functionality post-irradiation. DNA concentration measurements and gel electrophoresis were used to assess plasmid integrity, while transformation assays evaluated gene functionality and the impact of sub- inhibitory UV-C doses on bacterial competence in Escherichia coli and Citrobacter freundii. Results: Results showed a dose-dependent change in plasmid integrity and transformation efficiency. Significant DNA damage was observed at higher UV-C doses, particularly in the TOPO plasmid, which exhibited more pronounced structural damage compared to pUC19. This damage led to a loss of gene functionality, as evidenced by reduced transformation efficiency. Sub-inhibitory doses of UV-C irradiation did not enhance transformation frequency in Escherichia coli or Citrobacter freundii, indicating that UV-C does not promote bacterial competence. Conclusion: UV-C irradiation effectively damages plasmid DNA, reducing the functionality of ARGs. The study confirms that sub-inhibitory single doses of UV-C do not promote bacterial transformation through increased competence.