Salmonella typhimurium displays cyclical patterns of sensitivity to UV-C killing during prolonged incubation in the stationary phase of growth.

Stationary phase cells of Salmonella typhimurium were more resistant to killing by UV-C irradiation than those from the exponential phase. Analysis of the tolerance of cells taken at different stages of prolonged incubation as batch cultures to 60 or 100 J m(2) doses of UV-C revealed cycles of resistance and tolerance. The possible involvement of rpoS-controlled functions in mediating these cycles could be discounted because they were also detected in an rpoS minus mutant of S. typhimurium. The results are discussed in the context of heterogeneity in cells of stationary phase cultures of S. typhimurium.