Genetic Analysis of Clindamycin Resistance in Bacteroides Species

Abstract

The genetic basis of clindamycin and tetracycline resistance in species of Bacteroides was studied in 13 resistant clinical isolates; 10 isolates were resistant to high levels of clindamycin (>160 µg/ml) and three were resistant to low levels of clindamycin (5–20 µg/ml). All of the isolates were resistant to tetracycline. None of the strains with low level clindamycin resistance could transfer resistance to either antibiotic. Three isolates resistant to high levels of clindamycin transferred tetracycline resistance to a sensitive Bacteroides fragilis recipient, and one of these (strain 1126) also transferred high-level clindamycin resistance. None of the transfer-proficient strains of Bacteroides contained plasmid DNA. However, DNA homology was detected by hybridization between the clindamycin resistance plasmid pBF4 isolated in France and sequences in our high-level clindamycin-resistant strains from California. A common homologous 4.8 megadalton EcoR1 fragment was identified in the whole cell DNA of the transfer-proficient strain 1126 of B. fragilis and two other species of the B. fragilis group.