CONJUGAL TRANSFER OF THE 5-NITROIMIDAZOLE RESISTANCE PLASMID PIP417 FROM BACTEROIDES-VULGATUS BV-17 - CHARACTERIZATION AND NUCLEOTIDE-SEQUENCE ANALYSIS OF THE MOBILIZATION REGION

Three small 5-nitroimidazole (5-Ni) resistance plasmids (pIP417, pIP41 9, and pLP421) from Bacteroides clinical isolates are transferable by a conjugative process during homologous or heterologous matings. The m obilization properties of pIP417 originated from strain BV-17 of Bacte roides vulgatus were studied. The plasmid was successfully introduced by in vitro conjugation into different strains of Bacteroides and Prev otella species and could be transferred back from these various strain s to a plasmid-free 5-Ni-sensitive Bacteroides fragilis strain, indica ting that in vivo spread of the resistance gene may occur. The transfe r of plasmid pIP417 harbored by the Tc-r strain BF-2 of B. fragilis wa s stimulated by low concentrations of tetracycline or chlorotetracycli ne. This suggests a possible role for coresident conjugative transposo ns in the dissemination of 5-Ni resistance among gram-negative anaerob es. The nucleotide sequence of the 2.1-kb DNA mobilization region was determined. It contains a putative origin of transfer (oriT) in an A+T -rich-region, including three inverted repeats, and two integration ho st factor binding sites. The two identified mobilization genes (mobA a nd mobB) are organized in one operon and were both required for effici ent transfer, Southern blotting indicated that the mobilization region of plasmid pIP417 is closely related to that of both the erythromycin resistance plasmid pBFTM10 and the 5-Ni resistance plasmid pIP419 but not to that of the 5-Ni resistance plasmid pIP421.