UV-C inactivation of Cronobacter sakazakii

The purpose of this research was to study the effect of different factors on the resistance of Cronobacter sakazakii NCTC 9238 to UV-C light (which includes germicidal ultraviolet light at 254 nm) and to determine whether a combined treatment with heat would produce a synergistic effect for its inactivation. Growth temperature between 10°C and 37°C did not change the UV-C resistance of C. sakazakii. On the contrary, cells in the logarithmic phase of growth were more sensitive to UV-C light than in the stationary phase. The lethality of UV-C was independent of pH (between 3.0 and 7.0) and a(w) (between 0.94 and > 0.99) of the treatment media, but it exponentially decreased with the absorption coefficient (α). When applying a UV-C treatment of 27.1 J/mL at 25°C to C. sakazakii suspended in vegetable soup and apple juice, 1 and 2 log10 cycles of inactivation were barely achieved, respectively. However, the bactericidal effect of UV-C light increased with temperature. The lethality of the combined process was the result of a synergistic effect that was maximum at 52.5°C for apple juice and 55°C for vegetable soup. In conclusion, these results indicate that UV-C efficacy may be influenced by microbial growth conditions and food characteristics, and that its combination with heat may act synergistically against C. sakazakii.