Ultraviolet (UV)-C irradiation is a promising method for microbial eradication on surfaces. Major developments have taken place in UV-C light-emitting diodes (LEDs) technology. In this study, we examined the suitability of UV-C LED-based surface disinfection in hospitals. We tested the efficacy of UV-C LED surface treatment on different microorganisms dried on a carrier surface or in a liquid solution. The influences of soiling, shading, surface material, radiation wavelength, microbial load and species on the disinfection performance were investigated. UV-C LED caused a reduction of >5 log₁₀ levels of E. coli, S. aureus and C. albicans, whereas 3 log₁₀ reduction was observed for G. stearothermophilus spores. The components of the medium led to a reduced UV-C LED efficiency compared to buffered solutions. We observed that the microbial load and the roughness of the carrier surface had a major influence on the UV-C LED disinfection efficiencies, whereas shading had no impact on inactivation. This study showed that UV-C is suitable for surface disinfection, but only under certain conditions. We showed that the main factors influencing microbial inactivation through UV-C light (e.g., intrinsic and extrinsic factors) had a similar impact when using a UV-C LED radiation source compared to a conventional UV-C lamp. However, the potential of LEDs is contributed by their adjustable wavelength and customizable geometry for the decontamination of medical devices and surfaces, and thereby their ability to overcome shading effects.

Single substitutions or combinations of them alter the hydrolytic activity towards specific β-lactam-antibiotics and β-lactamase inhibitors of TEM-β-lactamases. The sequences and phenotypic classification of allelic TEM variants, as provided by the NCBI National Database of Antibiotic Resistant Organisms, does not attribute phenotypes to all variants. Some entries are doubtful as the data assessment differs strongly between the studies or no data on the methodology are provided at all. This complicates mathematical and bioinformatic predictions of phenotypes that rely on the database. The present work aimed to prove the role of specific substitutions on the resistance phenotype of TEM variants in, to our knowledge, the most extensive mutagenesis study. In parallel, the predictive power of extrapolation algorithms was assessed. Most well-known substitutions with direct impact on the phenotype could be reproduced, both mathematically and experimentally. Most discrepancies were found for supportive substitutions, where some resulted in antagonistic effects in contrast to previously described synergism. The mathematical modelling proved to predict the strongest phenotype-relevant substitutions accurately but showed difficulties in identifying less prevalent but still phenotype transforming ones. In general, mutations increasing cephalosporin resistance resulted in increased sensitivity to β-lactamase inhibitors and vice versa. Combining substitutions related to cephalosporin and β-lactamase inhibitor resistance in almost all cases increased BLI susceptibility, indicating the rarity of the combined phenotype.

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. 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 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. 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.