ANALYSIS OF BACTEROIDES SPECIES BY PYROLYSIS MASS-SPECTROMETRY

Two methods for the classification of isolates of the Bacteroides frag ilis group were compared in a study of 133 clinical isolates and 10 re ference strains. There was broad similarity between the pattern of clu sters in pyrolysis mass spectrometry (PyMS), which reflects whole-cell composition, and that in conventional tests, which reflect nutritiona l interactions with the environment. A single large cluster was resolv ed by both approaches; this cluster comprised mainly strains identifie d as B. fragilis and was surrounded by a multiplicity of small cluster s (42 in PyMS and 24 in conventional tests). Individual clusters corre sponding to strains identified as Bacteroides thetaiotaomicron and Bac teroides vulgatus, respectively, were found by both techniques. Howeve r, for the remainder of strains, little correlation was evident betwee n clustering in PyMS and that in conventional tests. Further compariso n with data obtained by sodium dodecyl sulfate-polyacrylamide gel elec trophoresis for this collection of strains showed equal levels of disa greement between classification based on whole-cell proteins and each of the classifications described here. In previous studies of other ge nera, PyMS-based and conventional test-based classifications showed go od agreement. It appears that the B. fragilis group presents intractab le problems in phenotypic characterization.