The effect of silver nanoparticles, non-ionizing (Ultraviolet), and ionizing radiation (X-rays) on macroscopic, bacterial single-species biofilms

Luna Hendrickx, Rob Van Houdt

Research output


A microbial biofilm is a dense, organized multidimensional object composed of multiple layers of the cells of microorganisms, which are encased in a secreted matrix of extracellular polymeric substances (EPS) often located on a substratum. The presence of biofilms in water-based systems is common and can cause problems (e.g. system damage and failure, biological and chemical contamination of fluent) in various sectors such as food processing, health care, space research and industrial sites. Since biofilms are reported to have increased resistance against stressors, the currently used antimicrobial treatments are much less effective. Therefore, our study aims to investigate the antimicrobial effects of several treatments: silver nanoparticles (AgNPs), non-ionizing ultraviolet (UV-C254 nm), ionizing X-rays, and two combined treatments (AgNPs exposure followed by UV-C or X-ray radiation) on agar-grown macroscopic (macroscopically visible biomasses) single-species bacterial biofilms of Cupriavidus metallidurans CH34 and Ralstonia pickettii SSH1. Additionally, the susceptibility of the CH34 biofilms against a stressor (UV-C254) was investigated relative to dispersed biofilms and planktonic cultures. A drastically decreasing susceptibility to UV-C254 radiation was observed as follows: planktonic cells > dispersed biofilms >>> biofilms. A side activity of the study was the selection of representative fluorescently tagged transconjugants of CH34 and SSH1 created by random transposon mutagenesis and no defects were observed based on growth rate and sensitivity to AgNPs relative to the wildtypes. The longest UV-C254 (60 minutes ≈ 255 kJ/m2) exposure and highest concentration of AgNPs (100 mg/L) were evaluated on CH34 biofilms and no significant reductions in cell survival number were observed. The combined treatment of AgNP (100 mg/L) exposure followed by 60-minute UV-C254 radiation resulted in a low but significant decrease in cell survival number (average log10 reduction of 1.0) relative to the untreated and single-treatment exposed CH34 biofilms. X-ray irradiation with 100 and 200 Gy was effective against both species biofilms since significant average log10 cell survival number reductions of 2.9 and 4.9 for CH34, and 1.7, and 4.0 for SSH1 were observed, respectively. AgNPs (50 mg/L) exposure followed by X-rays irradiation significantly reduced the cell survival number of both CH34 and SSH1 biofilms relative to the untreated biofilms. However, no significant reductions were observed relative to biofilms that were only X-ray irradiated, indicating no proof of synergistic radio-sensitizing effects between AgNPs and ionizing X-rays. For the single and combined ionizing radiation treatments, additional scanning electron microscopy analyses indicated cellular distress in both species.
Original languageEnglish
Awarding Institution
  • Avans university of applied sciences
  • Van Houdt, Rob, SCK CEN Mentor
  • Slotman, Michel, Supervisor, External person
  • Abdeljelil, Nissem, SCK CEN Mentor
Date of Award10 Mar 2023
StatePublished - 10 Mar 2023

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