Molecular and ecological aspects of antibiotic resistance in the Bacteroides fragilis group.

Current problems of antibiotic resistance in the Bacteroides fragilis group are reviewed. The original susceptibility (before 1976) of this group of strict anaerobic microorganisms to some beta-lactams, tetracyclines and lincosamides is presently severely damaged, and new mechanisms of resistance, such the enzymatic inactivation of chloramphenicol, seem to arise. Conjugative transfer of chromosomal resistance genes appears to be the main strategy for the spread of resistance and in various cases plasmids are involved. The origin of such resistance genes remains obscure. There is a possibility of gene exchange between Bacteroides and Enterobacteriaceae, but there are problems of plasmid maintenance and/or gene expression. In some cases a striking homology of the Bacteroides resistance determinants with those of Gram-positive organisms can be documented.