title: [Use of Autobac system in the study of the bacteriostatic effect of combinations of antibiotics (author's transl)].
abstract: After determining the LSI80 (light scattering index 80) concentration X and Y of two antibiotics for a given bacteria by an automated light scatter photometric method, we use the same process to test the bacteriostatic effect of all the combinations between the values 2X, X, X/2, X/4, X/8 and 2Y, Y, Y/2, Y/4, Y/8. The results read on the light scatter photometer are interpreted: --approximatealy by means of a simplified schematic diagram; --more precisely by drawing three curves: we begin with two inhibiton curves in order to determine the LSI50 concentrations (CLSI50) of each antibiotic, isolted and in the presence of defined concentrations of the complementary antibiotic; then from these CLSI50 we draw the bacteriostatic effect curve of the combination. When the LSI50 effect of the combination occurs with less than 50% of the CLSI50 of each isolated antibiotic, the combination is synergistic. It is antagonist if the bacteriostase is obtained with more than 100% of the CLSI50 of each isolated antibiotic. The intermediate percentages determine the indifferent effects. The additive effects come to an equilateral hyperbola passing through the points 50%-50%, 25%-75%. The Autobac system allows inoculum standardization, very simplified handlihg and automatic reading. It takes only 9 h to handle the complete process, including the determinations of the CLSI80 and the study of the combination. There is a high correlation between the results obtained and those given by the Patte and Chabbert "carre method".
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D001419:Bacteria / Q000187:drug effects*; D004338:Drug Combinations; D004926:Escherichia coli / Q000187:drug effects; D007711:Klebsiella pneumoniae / Q000187:drug effects; D008826:Microbial Sensitivity Tests / Q000295:instrumentation*; D011511:Proteus / Q000187:drug effects; D013211:Staphylococcus aureus / Q000187:drug effects
chemical_list: D000900:Anti-Bacterial Agents; D004338:Drug Combinations
vernacular_title: Application du système Autobac à l'étude de l'activité bactériostatique des associations d'antibiotiques.