Insertion of a novel DNA sequence, 1S1186, upstream of the silent carbapenemase gene cfiA, promotes expression of carbapenem resistance in clinical isolates of Bacteroides fragilis.
A small number of isolates of Bacteroides fragilis, an anaerobic pathogen of the human intestinal flora, carries a copy (or copies) of the carbapenemresistance gene, cfiA, which may be silent or expressed. We have studied the mechanism of activation of the frequently silent gene in in vitro-selected mutants and in clinical isolates. In both types of strains, activation was observed as the consequence of the insertion, at several possible sites, of a novel 1.3 kb insertion sequence, IS1186, immediately upstream of the carbapenemase gene. IS1186 has two open reading frames, on opposite strands, with coding capacities for a 41.2 kDa (ORF1) and a 22.5kDa (ORF2) protein. The 41.2kDa protein has homology with some proteins predicted from open reading frames of IS elements or DNA direct repeats of aerobic, but not anaerobic, Gram-negative bacteria. Upon insertion, transcription of cfiA was found to be driven from a promoter identified on the right end of IS1186. In one instance, insertion occurred into the putative ribosome-binding site of cfiA, leaving intact the tetranucleotide AGAA which is concluded to be a fully functional ribosome-binding site. Between 3 and 14 copies of IS1186 were detected per genome and the element was found, within the species B. fragilis, almost exclusively in the subgroup carrying the cifA gene.
Podglajen
I
I
Laboratoire de Microbiologie Médicale, Université Paris VI, France.
Breuil
J
J
Collatz
E
E
D001426:Bacterial Proteins / Q000096:biosynthesis* / Q000235:genetics; D001441:Bacteroides fragilis / Q000187:drug effects / Q000235:genetics*; D001483:Base Sequence; D015780:Carbapenems / Q000494:pharmacology*; D003001:Cloning, Molecular; D004251:DNA Transposable Elements; D004352:Drug Resistance, Microbial / Q000235:genetics; D004790:Enzyme Induction; D015964:Gene Expression Regulation, Bacterial; D008969:Molecular Sequence Data; D016133:Polymerase Chain Reaction; D011401:Promoter Regions, Genetic; D012270:Ribosomes / Q000378:metabolism; D014158:Transcription, Genetic; D001618:beta-Lactamases / Q000096:biosynthesis* / Q000235:genetics
D001426:Bacterial Proteins; D015780:Carbapenems; D004251:DNA Transposable Elements; D001618:beta-Lactamases; C063912:carbapenemase