Comparison of hyperinfectious and conventionally virulent salmonellae cytocidal activity upon infection of cultured macrophages.

aHyperinfectious S. Choleraesuis χ3246 and S. Bovismorbificans 158 as well as conventionally virulent S. Typhimurium reference strain 14028 were derived from stationary phase cultures under permissive (LPM pH 5.5 medium) or nonpermissive (LB medium) conditions for the hypervirulent phenotype. Cultured RAW264.7 murine macrophage cells were infected with bacteria at a multiplicity of infection (MOI) of 10∶1 or 100∶1 At 20 h post-infection, macrophages were stained with crystal violet, and bacterial cytocidal activity was quantified spectrophotometrically (577 nm) as described in Materials and Methods; high cytocidal activity is associated with low dye retention. Data given are representative absorbance values derived from each condition performed in triplicate. Standard error of triplicate means is <20%.
*Designates statistical significance for changes in cytocidal activity of hyperinfectious strains grown in LB versus LPM pH 5.5 medium relative to that found with reference strain S. Typhimurium 14028. Cytocidal activity was analyzed using analysis of variance; the change in cytocidal activity of the hyperinfectious S. Choleraesuis and S. Bovismorbificans were individually contrasted to the change in cytocidal activity of S. Typhimurium 14028 at each dose level. A significance level (P) of less than 0.05 was considered to be statistically significant.