Strain differentiation in Bacteroides fragilis by ribotyping and computer-assisted gel analysis

It is important to distinguish between Bacteroides fragilis strains as thei r virulence may vary and as B. fragilis seems to be a heterogeneous species . The aim of our study was to evaluate ribotyping for differentiation of 46 strains of B. fragilis and for assessment of strain heterogeneity within a nd between the two DNA-DNA homology strain groups established in this speci es. Twenty-seven strains belonged to Johnson's DNA homology group 1 and eig ht to group II. Eleven strains had not been assigned to any group (NI group ). DNA from all strains was cut with BglI, EcoRI and HindIII. Restriction f ragment length polymorphisms were investigated using a non-radioactive digo xigenin-labelled cDNA probe transcribed from Escherichia coli 16S + 23S rRN A. Ribotyping with BglI was most discriminatory, revealing a total of 26 di fferent patterns by visual inspection of gels. EcoRI followed with 20 patte rns and HindIII with 13 patterns. The gels from ribotyping were processed u sing the Dendron computer-assisted program. Strain clusters established usi ng Dendron were not always in agreement with homology-based strain groups. Strains of the NI group fell into both homology groups. Ribotyping, as it i s based on a relatively small portion of the genome, is useful for strain d istinction in epidemiological studies with B. fragilis, whereas DNA-DNA hom ology, using the entire genome, is more reliable for taxonomy. The Dendron computer-assisted program, which enabled objective assessment of multiple b anding patterns, increased the reliability of ribotyping.