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During enterohepatic circulation conjugated steroids are hydrolyzed by intestinal bacteria, further metabolized mainly by anaerobic bacteria, reabsorbed, reconjugated and delivered to the blood for renal excretion. 21-Dehydroxlylation of tetrahydrodeoxycorticosterone (THCOD) to pregnanolone is performed exclusively by Eubacterium lentum, a normal inhabitant of the intestinal flora. The concentration of E. lentum in feces can be determined from the highest dilution of fresh voided stool capable of 21-dehydroxylating THDOC. Such studies revealed that the concentration increases from 106/g wet feces during the first year of life to 108/g feces in the 7th and 8th decade. Colonization appears to be independent of diet since the organisms are present in babies whether breast-fed or on formula, in subjects on a “Western diet” and in Africans consuming a diet low in meat and fat.

Fifty recent clinical isolates of the B.fragilis group were tested to determine their susceptibility to ampicillin, carbenicillin, mezlocillin, azlocillin and piperacillin using an agar dilution technique. The influence of clavulanic acid on the penicillin susceptibility of these strains was determined by incorporating 2 mg/1 of clavulanic acid into test media. The production of beta-lactamase by the strains was determined by the nitrocefin test and their isoelectric points by focusing on Polyacrylamide gel. Piperacillin was generally the most active of the penicillins tested and carbenicillin the least active with MIC50 values of 8 and 32 respectively. Although mezlocillin was slightly more active than piperacillin against highly resistant strains (MIC 64 mg/1 ampicillin) it was less active against strains with moderate resistance (16–32 mg/1 ampicillin). The majority of resistant strains became at least fivefold more susceptible to ampicillin and carbenicillin in the presence of clavulanic acid, while this effect was less marked for the acylureidopenicillins. In 18% of strains the susceptibility to all five penicillins tested was virtually unaffected by the presence of clavulanic acid.