To assess the antimicrobial effect of a commercial UV-C system, knives inoculated with Escherichia coli and Staphylococcus aureus as well as naturally contaminated and collected from the wet and clean area of a slaughterhouse knives were examined. For inoculated knives, UVC treatment for 30 s reduced mean E. coli counts by 5.1 log CFU cm-2 and mean S. aureus counts by 4.5 log CFU cm-2. The presence of blood lowered mean reductions to 3.4 log CFU cm-2 for E. coli and to 2.5 log CFU cm-2 for S. aureus. The presence of fat had a greater negative impact on the efficacy of the UV-C treatment resulting in mean reductions <1.8 log CFU cm-2. For naturally contaminated knives from a slaughterhouse, total viable counts (TVC) before UV-C treatment varied considerably (wet area: 2.0-6.0 log CFU cm-2, clean area: 1.0-3.0 log CFU cm-2). UV-C treatment for 30s reduced mean TVC by 0.8 log CFU cm-2 (wet area) and 0.6 log CFU cm-2 (clean area), but the effect varied greatly between individual knives. Thus, under commercial conditions, the antibacterial effect of UV-C for the decontamination of knives is affected by the presence of additional contaminations like blood or fat. The adequate cleaning of the knives prior to UV-C decontamination is therefore of central importance.
Keywords: Inoculation; Knives; Natural contamination; Slaughterhouse; UV-C decontamination.