J. Breuil

Insertion of a novel DNA sequence, IS 1186, 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 carbapenem‐resistance 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 41.2kDa (ORF1) and a 22.5 kDa (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 cfiA gene.

Multidrug-Resistant Human and Animal Salmonella typhimuvium Isolates in France Belong Predominantly to a DT104 Clone with the Chromosome- and Integron-Encoded β-Lactamase PSE-1

Epidemiologic relationships were investigated in 187 ampicillin-resistant Salmonella typhimurium strains (86 human, 101 animal) from >2000 strains isolated in 1994. Of 23 resistance patterns, the most frequent (ampicillin [Am], chloramphenicol [Cm], tetracycline [Tc], streptomycin and spectinomycin [Sm], and sulfonamides [Su]) was found in 69.5% of human and 64.8% of animal isolates. Four beta-lactamase genes were identified, blaTEM (24%), blaPSE-1 (78%), and blaSHV and oxa-2 (each <3%). blaPSE-1 and the integrase gene, intI1, but not blaTEM, blaSHV or oxa-2, were chromosomeborne and found almost exclusively in the AmCmTcSmSu strains. In these, polymerase chain reaction mapping revealed two distinct integrons carrying blaPSE-1 or aadA2. Lysotypes, plasmid profiles, and restriction fragment length polymorphisms (IS200) were determined for 50 representative isolates and for 3 DT104 strains from the United Kingdom (UK). The phage type of the PSE-1-producing AmCmTcSmSu strains was 12 atypic, indistinguishable from that of the DT104 strains. The combined data indicate that the same multiresistant clone has spread through human and animal ecosystems in the UK and France.

Fluoroquinolone resistance linked to GyrA, GyrB, and ParC mutations in Salmonella enterica typhimurium isolates in humans.

We report two cases of infection with clonally unrelated, high-level ciprofloxacin-resistant, β-lactamase–producing strains of Salmonella enterica Typhimurium. Resistance was caused by four topoisomerase mutations, in GyrA, GyrB, and ParC and increased drug efflux. Ciprofloxacin treatment failed in one case. In the second case, reduced susceptibility to third-generation cephalosporins occurred after initial treatment with these drugs and may explain the treatment failure with ceftriaxone.

Multiple Mobile Promoter Regions for the Rare Carbapenem Resistance Gene of Bacteroides fragilis

Two novel insertion sequences (IS), IS1187 and IS1188, are described upstream from the carbapenem resistance gene cfiA in strains of Bacteroides fragilis. Mapping, with the RACE procedure, of transcription start sites of cfiA in these and two other previously reported IS showed that transcription of this rarely encountered gene is initiated close to a variety of B. fragilis consensus promoter sequences, as recently defined (D. P. Bayley, E. R. Rocha, and C. J. Smith, FEMS Microbiol. Lett. 193:149-154, 2000). In the cases of IS1186 and IS1188, these sequences overlap with putative Esigma(70) promoter sequences, while in IS942 and IS1187 such sequences can be observed either upstream or downstream of the B. fragilis promoters.