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The author tested parallely 35 Bacteroides fragilis strains by the agar diffusion method and disk technique. A notable discrepancy appears between these two procedures. No regression line can be constructe and the inhibition diameter measurement is unable to class the strain in "susceptible" or "resistant". A literature review on this theme shows that the dissociation between these two techniques were more frequent with anaerobic strains than aerobic for SMX + TMP as others antibiotics. The MIC determination by an agar dilution is the only able to these studies.

The minimum inhibitory concentrations (MIC) of nalidixic acid were determined for thirty-four strains of Clostridium sp. by an agar dilution technique. The MIC range of Clostridium perfringens ran from 0.03 microgram/ml to 64 microgram/ml, according to a bimodal distribution. One half of the strains was inhibited by 0.25 microgram/ml. 64 microgram/ml was able to inhibit all the strains tested. The author suggests a systematic utilization of media with and without 40 microgram/ml nalidixic acid. These two media were parallely inoculated with clinical specimens where anaerobic bacteria were suspected, and allowed the isolation of gram negative anaerobes.

The authors have used two different methods for the identification of 45 strains of stric anaerobic gram negative rods: a study of biochemical characters by the API 20 anaerobic kit, and system proposed by SUTTER and FINEGOLD (susceptibility to discs loaded with antibiotics associated with some simple biochemical characters). A good correlation has been observed between those two techniques. However, a precise diagnostic can be given only by a whole study of biochemical characters, as proposed by the system API 20 Anaerobic.