The effect of growth temperature on the UV-C sensitivity of E. coli DH5a and L. plantarum BFE 5092 in QSRS is presented in Fig. 2. After incubating E. coli DH5a below the optimum growth temperature of 37 C, cells were more resistant to UV-C at subsequent treatments, which indicates a cross-protecting effect of the cold response and UV-C light in E. coli DH5a (Fig. 2a). The higher growth temperature of 45 C on the other hand led to a synergistic effect between the parameters of the temperature and UV-C irradiation. A higher reduction rate of E. coli DH5a was observed for cells grown at higher temperature when compared to cells grown at 37 C. The effect of growth temperature on the inactivation efficiency of E. coli DH5a may be explained by the differences in cytoplasmic membrane fluidity, which has an essential role in DNA
excision repair. However, no considerable difference in UV-C sensitivity could be observed for L. plantarum BFE 5092 incubated at different temperatures (Fig. 2b)
(Chung et al., 2006; Kolter et al., 1993). Bucheli-Witschel et al.
(2010) reported a dependence of growth rate on UV-C sensitivity
of E. coli K12. Therefore, in batch cultures, the UV-C resistance of
E. coli K12 decreases during the mid-exponential phase and reaches
a maximum resistance just before cells enter the stationary phase