FIG. 1.

(A) Levels of cytoplasmic nucleosomal fragments in macrophages infected with S. enterica serovar Typhimurium strains χ3306 (clpPX⁺) and CS2007 (ΔclpPX). RAW264.7 cells were infected with bacteria at a multiplicity of infection of 10. At 6 h after infection, the levels of histone-associated cytoplasmic DNA fragments were measured by quantitative enzyme-linked immunosorbent assay using an antihistone antibody as described in Materials and Methods. The data are the means and standard derivations for each strain tested in triplicate. (B) Invasion efficiency of strains χ3306 (clpPX⁺) and CS2007 (ΔclpPX). Cultured Intestine-407 cells were used to assess invasiveness as described in Materials and Methods. The data are the means and standard derivations for each strain tested in triplicate. Invasion efficiency was expressed as the ratio of the number of intracellular bacteria to the number of bacteria adhering to the cultured cells.