title: Evaluation of antimicrobial susceptibility testing of bacterial mixtures using agar dilution technique.
abstract: Antimicrobial susceptibilities of artificially created bacterial mixtures were investigated using an agar dilution technique with a standardized inoculum. Three types of combinations, ie, mixtures containing a susceptible and a resistant organism, and those containing two susceptible or two resistant organisms were tested. Organisms used in the study were previously isolated from a variety of clinical specimens. Both gram-positive and gram-negative organisms were included in the evaluation. Of the 42 combinations containing a susceptible and a resistant organism, 30 (73.8 percent) appeared as resistant, and 12 (26.2 percent) as susceptible. Of the 50 susceptible-susceptible combinations, 8 (16 percent) appeared as resistant and 42 (84 percent) as susceptible. However, in the case of 17 resistant-resistant combinations, 16 (94.2 percent) appeared as resistant and only 1 (5.8 percent) as susceptible. "Direct" or "primary" antimicrobial susceptibility testing of the clinical specimens, which are likely to contain a variety of microorganisms, can be unreliable and should not be used as a guide to antimicrobial therapy.
mesh_terms: D000362:Agar; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D001419:Bacteria / Q000187:drug effects*; D004755:Enterobacteriaceae / Q000187:drug effects; D007201:Indicator Dilution Techniques; D008826:Microbial Sensitivity Tests / Q000379:methods*; D013210:Staphylococcus / Q000187:drug effects; D013291:Streptococcus / Q000187:drug effects
chemical_list: D000900:Anti-Bacterial Agents; D000362:Agar