Chromosomal restriction endonuclease analysis and ribotyping of Bacteroides fragilis

We have analysed the restriction fragment length patterns of chromosomal DNA and of ribosomal RNA (rRNA) genes in order to investigate the clonal distribution within Bacteroides fragilis isolates. Eighteen blood culture isolates from 18 patients and 4 faecal isolates from 4 subjects were examined. Chromosomal restriction endonuclease analysis (REA) was performed by separating BamHI-generated DNA fragments using polyacrylamide gel electrophoresis (PAGE). Ribotyping was accomplished by hybridizing EcoRI-treated genomic DNA subjected to conventional REA on agarose to a radiolabelled probe obtained from 16+23S rRNA of E. coli. All 22 isolates could be differentiated by their REA patterns with a varying percentage of similar fragments. Analysis of the rRNA gene patterns displayed heterogeneity, and revealed 14 ribotypes among the 18 blood culture isolates and 3 among the 4 faecal isolates. The predominant ribotype among the clinical isolates was also shared by one faecal isolate. The results suggest that no particular clones are predominantly responsible for systemic infection.