Document Type


Publication Date

Fall 8-14-1950


The purpose of this work was to determine the susceptibility of strains of viridans streptococci and enterococci to sulfathiazole, aureomycin, bacitracin, penicillin, and streptomycin; and to determine whether their susceptibility to these agents was related to other biochemical properties. Since previous work had indicated that trained sulfathiazole-resistant viridans streptococci acquired properties similar to those characteristic of enterococci, it followed that strains trained to resistance to penicillin, streptomycin, aureomycin, and bacitracin should also be compared in biochemical properties to naturally-resistant enterococci. Investigation of cross-resistance among these strains seemed of further importance because of its possible clinical applications. A study of the interrelationship between susceptibility and other biochemical properties commonly used for the identification of the organisms might produce several useful results. Mew and better tests for identification might be discovered, possible agents for trial in treatment of the changed organisms might be indicated, and possible changes in organisms subjected to the chemotherapeutic agents might be anticipated. Finally, it was of interest to compare all changes in both the parent and the trained resistant strains for a possible explanation of the increased resistance. Gale had found larger amounts of free glutamic acid in strains of staphylococci naturally resistant to sulfathiazole than in susceptible strains, if the young cells were examined. Less glutamic acid was found in penicillin-resistant cells. He did not examine cells resistant to other antibiotics. Therefore, the glutamic acid content of cells trained to resistance to sulfathiazole, penicillin, streptomycin, and aureomycin was determined in this study. The work was carried out in two parts. First, the biochemical properties and susceptibility to sulfathiazole, aureomycin, bacitracin, penicillin, and streptoaycin was determined for 40 strains of viridans streptococci and enterococci. Thirty-seven strains of the organisms were isolated from pathological material and 3 strains were used as controls, one Streptococcus fecalis (A.T.C.C. #9790) and two viridans streptococci, Streptococcus "MG" and Streptococcus "SBE", Secondly, the biochemical properties and susceptibility to the chemotherapeutic agents was determined for trained resistant strains to sulfathiazole, aureomycin, penicillin, and streptomycin. No bacitracin-resistant strains were studied, as even after prolonged exposure to bacitracin, no resistant variants developed. The glutamic acid content was determined manometrically for viridans streptococci, enterococci, and resistant variants to sulfathiazole and the antibiotics. The biochemical characteristics best suited for differentiating between viridans streptococci and enterococci, as indicated in this study, area growth in broth incubated at 45°C for 24 hours, the reduction of 0.1% methylene blue milk, growth in 6.5% NaCl broth, and growth on 40% bile agar. The enterococci were more resistant to all of the chemotherapeutic agents used than were the viridans streptococci. The much greater resistance of the enterococci to sulfathiazole and penicillin indicated the possibility of using definite concentrations of these in broth as added criteria for identification. It was found that all of the enterococci and none of the viridans streptococci would grow in concentrations of 10 mg/cc of sulfathiazole in broth and 2 units/cc of penicillin in broth. Results of the in vitro tests for susceptibility to the five agents indicate that infections due to viridans flight respond to all of the chemotherapeutic agents tested, but those due to enterococci might best be treated with bacitracin or aureomycin. The most interesting findings in the development of resistant strains were the cross—resistance and the difference between the streptomycin-resistant variants as compared to the others. Some increase in resistance to all the agents was shown z by the sulfathiaole-resistant variants. Increase in resistance to other agents was also shown by those strains trained to resistance to penicillin and aureomycin, but this was not generally true of the streptomycin-resistant strains. The variant strains selected by sulfathiazole, aureomycin, and penicillin all showed the same biochemical properties as a typical enterococcus. Those selected by streptomycin varied in their biochemical properties and often did not have the properties of enterococci. The results of the glutamic aoid determinations showed that appreciable amounts are found free inside those cells which have acquired sulfathiasole resistance. Whether this resistance has been induced by sulfathiazole or accompanies increased resistance to other agents makes no difference. Whether the resistance is due to the increase in internal glutamic acid or whether this is merely a result of other changes which determine the organism's resistance, is not answered by this study. The viridans streptococci tested, and the streptomycin-resistant variants showed no free glutamic acid at any stage of growth.