Penicillin resistant staphylococci inoculum effect

1. Staphylococcus aureus strains have been obtained from blood cultures and kept for further study. 2. All Staphylococcus aureus strains have been bacteriophage typed with no common grouping noticeable. 3, Disk sensitivity testing methods have been used to demonstrate the inoculum effect. Importance to clinical application has been mentioned. 4. A pour plate method of testing for penicillin sensitivity has been described and results of strains tested recorded. 5. An attempt was made to demonstrate a mixed culture of cells with a varying sensitivity to penicillin within a given strain. No appreciable difference in penicillin sensitivity could be demonstrated. 6. A ditch method of penicillin sensitivity testing was used to attempt to demonstrate the protection of a sensitive organism from the action of penicillin by a resistant staphylococcus. No protection could be detected. 7. Sodium azide was incorporated in various concentrations into the culture medium. The azide had an effect on the cell reproduction but results were not obtained in relation to the inoculum effect. 8. A modified pour plate method demonstrated a direct relationship between nximber of organisms in the 86 inoculum and the degree of resistance of an individual strain of Staphylococcus aureus. 9. Combination tube and pour plate methods of penicillin sensitivity testing demonstrated a stasis period after which growth occurs at a normal rate. The length of static period varies indirectly with the number of organisms in the inoculum. 10. Penicillin assays were carried out by using a chemical method. This method was discarded because of its insensitivity in the lower penicillin concentrations. 11. A biological assay method for penicillin was used to assay for remaining penicillin after incubating the penicillin with staphylococci at 37?C. 12. The adsorption of penicillin to stpahylococci was measured using the bio assay method. 13. The effects of Mg++ and Ca++ on penicillin adsorption to staphylococci were studied. 14. Dimethoxyphenyl penicillin was used in the pour plate method of testing for penicillin sensitivity in place of penicillin G, No inoculum effect was observed. 15. The lethal effects of combinations of Dimethoxy-phenyl penicillin and penicillin G on staphylococci was studied in vitro.