ヒト腸管より分離したBacteroides fragilis菌株による胆汁酸代謝

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Sixty-one strains of Bacteroides fragilis recovered from the human intestinal tract were tested for ability to split conjugates of deoxycholic acid and to attack cholic acid (CA) and chenodeoxycholic acid (CDCA). When classified into subspecies, the isolates consisted of 18 B. fragilis ss. fragilis, 17 B. fragilis ss. thetaiotaomicron, 25 B. fragilis ss. vulgatus, and one B. fragilis ss. ovatus. Three reference strains, two B. fragilis ss. fragilis and one B. fragilis ss. ovatus, were also included in the study.To test for bile acid transformation, microorganisms were cultivated in a modified peptoneyeast extract broth containing one of the bile acids. After anaerobic incubation for 36 hours to six days, bile acids were extracted from the broth with ethyl acetate. After methylation, analysis was done by gas-liquid chromatography on a 3% QF-1 column.All the 64 strains examined deconjugated glycodeoxycholate, though to different extents. Thirty of them dehydrogenated the 7α-hydroxyl group in both CA and CDCA. The percentage of conversion to the respective keto acids was compared between the two bile acids. None of the 25 strains of B. fragilis ss. vulgatus were capable of oxidizing the 7α-hydroxyl group of the two primary bile acids, in contrast to 17 positive strains among the 20 strains of B. fragilis ss. fragilis and 12 among the 17 of B. fragilis ss. thetaiotaomicron. Ursodeoxycholic acid, a 7β-epimer of CDCA, was not affected by any of the 64 strains. No strains were active in the 7α-dehydroxylation of CA or CDCA under the test conditions, where the positive strain, C. sordellii 4709, showed this activity toward the two bile acids.
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ヒト腸管より分離したBacteroides fragilis菌株による胆汁酸代謝

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