The effect of cultural conditions on the susceptibility of staphylococci to killing by the cationic proteins from rabbit polymorphonuclear leucocytes.

Seventeen strains of and 12 strains of were tested for their susceptibility to killing by the cationic proteins from rabbit polymorphs, when cultured under different conditions. The resistance of the V strain of of Adlam, Pearce and Smith (1970) was confirmed and shown to be independent of the conditions of growth. All other strains were more or less susceptible when grown in brain heart infusion broth or proteose peptone broth, with or without lactate, but were highly resistant when grown in these media supplemented with glucose. The resistance was not due to changes in pH. Susceptibility was restored when the organisms were again grown on broth media without glucose. Since preliminary observations indicate that the cationic proteins inhibit the action of NADH oxidase, it is suggested that the organisms are susceptible only when growth depends on aerobic respiration. If the culture contains an energy source such as glucose which can be utilized by an alternative pathway, the organism loses its susceptibility. After culture in a chemically defined medium, most strains of were resistant and most strains of were susceptible to the cationic proteins. The resistance of was not removed by adding vitamins, purine and pyrimidine bases or serum (from clotted cell free plasma) to the growth medium but was abolished by proteose peptone. The active fraction in proteose peptone was partially excluded by Sephadex G-25, but not by G-10. Some of its activity was lost on acid hydrolysis. The cause of the difference in susceptibility between and after growth in a chemically defined medium or in this medium supplemented with serum is not known. It may be related to the known difference between these organisms in their ability to grow in serum from clotted blood, which contains similar cationic proteins.