Osmotic and desiccation tolerance in Escherichia coli O157:H7 requires rpoS (σ(38))

The contribution of RecA, Dps, and RpoS to survival of Escherichia coli O157:H7 during desiccation and osmotic stress was determined in Luria-Bertani broth with 12 % NaCl (LB-12) at 30 and 37 °C, on filter disks at 23 and 30 °C, and in sterile bovine feces at 30 °C. RecA did not significantly contribute to survival in any condition or temperature. The contribution of Dps to survival was only significant in LB-12 at 37 °C. RpoS was necessary for survival during desiccation and osmotic stress, and survival of the RpoS mutant was significantly less than the parent in all conditions and temperatures. The RpoS mutant survived up to 21 days in bovine feces, <4 days on filter disks, and >8 and <4 days in LB-12 at 30 and 37 °C, respectively. The parent, ΔrecA, dps, and dps/ΔrecA mutant strains survived >8 days in LB-12, >28 days on filter disks, and >28 days in bovine feces. Increased incubation temperatures were associated with decreased survival. E. coli O157:H7 can persist in desiccating and osmotically challenging environments, especially sterile feces, for an extended period time.