Differentiation of Bacteroides fragilis species by gas chromatographic detection of phenylacetic acid.

Of 382 strains tested, 261 strains of the species Bacteroides fragilis, B. thetaiotaomicron, B. ovatus, and B. distasonis produced phenylacetic acid; the remaining strains, belonging exclusively to the species B. vulgatus, failed to do so. This differentiation characteristic may be useful in routine clinical bacteriology.