[The combination effect of ampicillin and dicloxacillin on the strains of Bacteriodes fragilis isolated from clinical specimens (author's transl)].

The antimicrobial activities of ampicillin (ABPC) and dicloxacillin (MDIPC) alone were tested in 100 strains of B. fragilis isolated from clinical specimens, and combined activity of ABPC and MDIPC was investigated employing a chequer board titration method (Box method) with agar plates and liquid media. The following results were obtained. 1. Of the 100 strains tested, approximately 33% were shown to have MICs of ABPC greater than 100 mcg/ml, whereas 92% of strains were greater than 100 mcg/ml to MDIPC. 2. In the combination, antimicrobial activities were demonstrated additive or synergistic action in almost strains tested. 3. A combined effect of these drugs was proved by agar dilution method for the strains, for which the same effect was shown by the tube dilution method. 4. For ABPC-resistant strains, no increase in antibacterial activity of these drugs by combination was demonstrated.