title: Susceptibility testing of anaerobic bacteria. Regression lines for six antibiotics determined with and without prediffusion.
abstract: The relationship between susceptibility testing by an agar dilution test and a tablet diffusion test was studied for 60 anaerobic bacteria (20 B. fragilis, 20 anaerobic cocci, 20 Clostridium species). For cefoxitin, no prediffusion and prediffusion times of one h, three h, 12 h, 24 h and 48 h were examined. For metronidazole, erythromycin, clindamycin, penicillin and imipenem, only 24 h prediffusion and no prediffusion were studied. Measurements were made after incubation for 24 h and 48 h. Prediffusion improved the correlation for all antibiotics tested, and 24 h prediffusion gave the best results. The slope of the regression line increased and the influence of the individual growth parameters on zone size was reduced. Prediction of susceptibility based on three zone breakpoints to estimate MIC was also better with 24 h prediffusion. However, the variation about the regression line for many of the antibiotics was still extremely high. Measurements after 24 h and 48 h incubation times showed almost identical regression equations, except for erythromycin, where the regression lines differed.
authors.affiliation: Department of Clinical Microbiology, Frederiksberg Hospital, University Hospital of Copenhagen, Denmark.
authors.forename: J E
authors.initials: JE
authors.lastname: Jansen
authors.forename: A
authors.initials: A
authors.lastname: Bremmelgaard
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology* / Q000592:standards; D001421:Bacteria, Anaerobic / Q000187:drug effects* / Q000254:growth & development / Q000502:physiology; D002440:Cefoxitin / Q000494:pharmacology / Q000592:standards; D002981:Clindamycin / Q000494:pharmacology / Q000592:standards; D015169:Colony Count, Microbial; D004917:Erythromycin / Q000494:pharmacology / Q000592:standards; D015378:Imipenem / Q000494:pharmacology / Q000592:standards; D008795:Metronidazole / Q000494:pharmacology / Q000592:standards; D008826:Microbial Sensitivity Tests; D010406:Penicillins / Q000494:pharmacology / Q000592:standards; D012044:Regression Analysis; D013997:Time Factors
chemical_list: D000900:Anti-Bacterial Agents; D010406:Penicillins; D008795:Metronidazole; D002981:Clindamycin; D004917:Erythromycin; D002440:Cefoxitin; D015378:Imipenem