Effects of UVC Treatment on Biofilms of Escherichia coli Strains Formed at Different Temperatures and Maturation Periods

In the present study, the biofilm formation and ultraviolet-C (UVC) resistance characteristics of <i>Escherichia coli</i> isolated from an occluded biliary stent were compared with those of four <i>E. coli</i> O157:H7 strains (ATCC 35150, 43889, 43890, and 43895). To evaluate biofilm formation, the <i>E. coli</i> isolated from a stent and four <i>E. coli</i> O157:H7 strains were incubated at 37, 25, and 15 °C for 7 days, revealing that peak biofilm formation occurred at 37 °C (day 1), 25 °C (day 3), and 15 °C (day 5), with the stent-isolated strain consistently exhibiting significantly higher biofilm cell counts than the others (<i>p</i> < 0.05). The UVC treatment was less effective at reducing viable biofilm cells as the formation temperature decreased, with the stent-isolated <i>E. coli</i> biofilm formed at 15 °C showing the lowest reduction levels. Exopolysaccharide quantification revealed that all <i>E. coli</i> strains produced more extracellular polymeric substances (EPSs) at lower temperatures, with the stent-isolated <i>E. coli</i> biofilm formed at 15 °C showing significantly higher EPS levels than the other strains (<i>p</i> < 0.05), potentially explaining its greater UVC resistance. Based on these results, it was confirmed that the biofilm formed by the <i>E. coli</i> isolated from the stent at 15 °C exhibited the highest resistance to UVC, which can be attributed to its elevated exopolysaccharide production. This study demonstrates that both temperature and maturation period significantly influence <i>E. coli</i> biofilm characteristics and provides valuable insights into <i>E. coli</i> isolated from the stent, which may pose a risk of cross-contamination in food-related environments.