PLASMIDS PIP419 AND PIP421 FROM BACTEROIDES - 5-NITROIMIDAZOLE RESISTANCE GENES AND THEIR UPSTREAM INSERTION-SEQUENCE ELEMENTS

The genetic organization of two different 5-nitroimidazole (5-Ni) resi stance genes was investigated: nimC and nimD from Bacteroides plasmids pIP419 and pIP421, respectively. The nimC gene (492 bp) and the nimD gene (495 bp) directed the synthesis of polypeptides with deduced mole cular masses of 18.37 kDa and 18.48 kDa, respectively, The predicted p roteins showed 67-83% identity and 78-91% similarity with the products of two other nimA and nimB genes previously described and could be de rived from a common ancestral gene, An insertion sequence element (IS1 170) was identified upstream of the nimC gene. IS1170 is 1604 bp in le ngth and is flanked by imperfect inverted repeats (15 bp). IS1170 is s imilar to the Bacteroides insertion sequence element IS942 with an ide ntity of 70% at the nucleotide level. The single copy of 151170 presen t on plasmid pIP419 is integrated 24 bp upstream of the initiation cod on of nimC. Similar genetic organization was found on plasmid pIP421. One copy of another insertion sequence (IS1169) was found 4 bp upstrea m of the first ATG codon of the nimD gene, This element (1325 bp) show s a strong homology at the nucleotide level (70% identity) with IS1186 and IS1168 found to be associated with the Bacteroides carbapenem res istance gene cfiA, and the 5-Ni(r)genes nimA and nimB, respectively. T here is strong evidence that, as in the case of the cfiA gene, the tra nscription of the four nim genes so far studied is directed by outward -oriented promoters, carried on the right ends of the different insert ion sequence elements.