Changes in Salmonella enterica serovar Oranienburg viability caused by NaCl-induced osmotic stress is related to DNA relaxation by the H-NS protein during host infection.

The NaCl sensitivity of Salmonella enterica serovar Oranienburg strains depends on their origin. We found previously that food- and patient-origin isolates in an outbreak were, respectively, NaCl-resistant and NaCl-sensitive, and the NaCl-resistant strain of food-origin isolates became NaCl-sensitive after passage of the strain through mice [FEMS Microbiol. Lett. 212 (2002) 87]. Here, we report that this phenotypic difference is mainly dependent on topological changes regulated by H-NS, a bacterial histone-like nucleoid protein that binds non-specifically to DNA. That is, this phenotypic difference was caused by changes in DNA topology during infection of the host. Based on these findings, we propose this mechanism has a key role in promoting the survival of Salmonella under osmotic stress.