Figure 6. Serum susceptibility of B. petrii 1 and B. petrii 3.

Bacterial colonies grown on SBA were resuspended in 1% proteose peptone - phosphate-buffered saline (PP-PBS) to a concentration of 1×10⁷ CFU/ml. A 100-µl aliquot was then combined with an equal volume of 10% normal human serum (NHS) diluted in 1% PP-PBS. A 1% PP-PBS (0% serum) solution and heat-inactivated (56°C for 1 hour) normal human serum (HI-NHS) served as controls. Samples were incubated for 2 hours at 37°C with shaking. After incubation, samples were serially diluted, plated onto sheep blood agar plates, and grown 24–48 h at 37°C to determine the number of CFU and calculate % of survival.