Presence of two unique genes encoding macrolide-lincosamide-streptogramin resistance in members of the Bacteroides fragilis group as determined by DNA-DNA homology

The relationship of a previously described, plasmid-encoded macrolide-lincosamide-streptogramin (MLS) resistance determinant to Bacteroides fragilis group clinical isolates from 11 different patients with bacteroides infections was assessed using in situ hybridization. Most of the strains were found to have DNA sequences homologous with the bacteroides MLS plasmid, pBF4, but this homology was exclusively to chromosomal DNA. Two organisms isolated from different sites in a single patient did not share homology with the plasmid, and probably represent a second type of MLS gene. The MLS resistance plasmids, pBF4 (from Bact. fragilis) and pE194 (from Staphylococcus aureus), did not share homologous sequences; therefore at least one of the bacteroides MLS genes is different from that found in Gram-positive organisms.