FIG. 4.

BP536 resistance to naïve serum after mouse infection with and without divalent cation chelation. Liquid culture BP536 samples were grown to mid-log phase in SS broth (open bars). BP536 samples were generated by intranasal inoculation of four BALB/c mice with 5 × 10⁵ CFU, followed by recovery and homogenization of the lungs in PBS at 5 days postinoculation (solid bars). The bacteria were diluted to a concentration of 1 × 10⁴ CFU/ml and treated with 90% naïve rabbit serum alone, serum with EDTA, or serum with EGTA plus MgCl₂ for 1 h at 37°C. Serum resistance is expressed as the percentage of bacteria that survived; the error bars indicate standard deviations. All samples were run in triplicate. Two asterisks indicate that the P value was <0.001 when the data were compared to the data for a control sample without a chelator present.