Identification and DNA sequence of the mobilization region of the 5-nitroimidazole resistance plasmid pIP421 from Bacteroides fragilis

Abstract

The nucleotide sequence of the DNA mobilization region of the 5-nitroimidazole resistance plasmid pIP421, from strain BF-F239 of Bacteroides fragilis, was determined. It contains a putative origin of transfer (oriT) including three sets of inverted repeats and two sequences reminiscent of specific integration host factor binding sites. The product of the mobilization gene mob 421 (42.2 kDa) is a member of the Bacteroides mobilization protein family, which includes the MobA of pBI143, NBUs, and Tn4555. Sequence similarity suggests that it has both oriT binding and nicking activities. The transfer frequency of pIP421 in a B. fragilis donor strain possessing a Tc r or Tc r Em r -like conjugative transposon was significantly enhanced by tetracycline. Moreover, the mobilization region of pIP421 confers the ability to be mobilized from Escherichia coli by an IncP plasmid.Moderate resistance of Bacteroides spp. to 5-nitroimidazole (5-Ni) has only recently appeared in some clinical isolates (2). The resistance of these strains is due to the presence of specific 5-Ni resistance nim genes (18). Epidemiological data have shown that in France the frequency of 5-Ni-resistant Bacteroides strains is increasing. The spread of the resistance among these significant opportunistic pathogens, which are responsible for various infectious diseases, could be explained by the fact that nim genes are usually found on mobilizable genetic elements, either in non-self-transferable plasmids or on the chromosome. Three such 5-Ni r plasmids (pIP417, pIP419, and pIP421) have already been characterized, and the mobilization properties of one of them, pIP417, has been fully analyzed (25). The mobilization region of plasmid pIP417 is closely related to that of both the erythromycin resistance plasmid pBFTM10 from Bacteroides fragilis (8) and pIP419 but not to that of pIP421. Conjugal transfer of pIP417 is stimulated by tetracycline (TET) in a strain carrying a conjugative transposon of the Tc r Em r DOT family on the chromosome. These elements possess regulatory genes involved in control of their self-transfer activities and can also interfere with the regulation of coresident mobilizable plasmids (22). They could thus be responsible for the rapid spread of plasmid-borne resistance genes. We therefore examined the transfer properties of pIP421 and compared them with those of mobilizable genetic elements previously identified in Bacteroides species. The experimental procedures used in the present study have been previously described (25).The conjugal transfer properties of plasmid pIP421 in B. fragilis. The conjugal transfer properties of pIP421, native to the strain BF-F239 (5-Ni r Tc r Em r ) of B. fragilis, were first investigated through mating experiments in which the 5-Ni s strain BF-2 of B. fragilis was used as the recipient (Table 1). When the donor strain was pregrown in the absence of inducer, pIP421 was transferred at a low frequency (3.5 ϫ 10 Ϫ8 per recipient). The frequency was increased up to 100-fold if TET or chlortetracycline (ClT...

Multiple Gene Products and Sequences Required for Excision of the Mobilizable Integrated Bacteroides Element NBU1

“…MobN1 is a distant relative of the IncP TraI (16,30). Genes similar to mobN1 have also been found on the mobilizable Bacteroides transposon Tn4555, the mobilizable Bacteroides plasmids pBI143 and pIP421, and the mobilizable grampositive bacterial plasmid pMV158 (9,30,31,33,40). All of the small Bacteroides plasmids and the 10-to 12-kbp integrated elements are mobilized not only by Bacteroides conjugative transposons but also by the IncP plasmids of the enterics (15-17, 24, 28, 30, 40, 41).…”

The Transfer Origin for Bacteroides Mobilizable Transposon Tn 4555 Is Related to a Plasmid Family from Gram-Positive Bacteria

“…This region was required in cis for the transfer of pBI143 (29,30). Likewise, in a 217-bp region of pIP421 (bp 450 to 468) known to be required in cis for transfer (34), there a All matings were triparental matings with a strain containing the plasmids indicated, HB101 (1) as the recipient, and the RK231 conjugation helper strain (5). Matings were performed aerobically as described previously except that incubations were for only 4 h prior to plating on selective medium (28).…”

Impact of Dental Plaque Biofilms in Periodontal Disease: Management and Future Therapy

“…Four genes, nimA, nimB, nimC, and nimD, chromosomal or plasmid located, able to confer moderate to high-level metronidazole resistance have been revealed in Bacteroides sp. [117].…”