A COMPARISON OF RAT AND RABBIT SERA BACTERICIDINS ACTIVE AGAINST STAPHYLOCOCCI

Abstract

The respiration and growth of 5 strains each of Staphylococcus aureus and Staphylococcus epidermidis in fresh normal rat and rabbit sera were measured. S. aureus grew and oxidized the sera of these animals better than S. epidermidis. Both S. aureus and S. epidermidis grew and respired more actively in rabbit than in rat serum. The antibacterial activity of rat or rabbit serum was stable to heating at 56 °C for 1 h, but its activity was destroyed after heating at 60 °C for 2 h. Treatment of rat and rabbit sera with 0.4 M sodium citrate drastically reduced the antibacterial activity of these sera. Once the sera had been treated with sodium citrate or oxalate, addition of equimolar solutions of calcium chloride or magnesium chloride failed to restore the antibacterial activity of rat and rabbit sera. Addition of ferric ions at concentrations which are not normally found in rat and rabbit sera reversed the inhibitory activity of these sera, thus allowing coagulase-negative strains of staphylococci to grow well in rat and rabbit sera. The antibacterial agent of rat or rabbit serum was absorbed by heat-killed cells of S. aureus and S. epidermidis; treatment with bentonite at a concentration of 100 mg/ml absorbed the antibacterial agent from rabbit serum but only partially from rat serum. The high levels of the antibacterial agent in rat serum may explain the partial removal of this agent by bentonite and may contribute to the marked resistance of the rat to staphylococcal infection.