Association of IS26-composite transposons and complex In4-type integrons generates novel multidrug resistance loci in Salmonella genomic island 1.
OBJECTIVE
Clinical isolates of Salmonella enterica serovar Haifa and Newport, which displayed extended multidrug resistance phenotypes, were investigated for the presence of Salmonella genomic island 1 (SGI1) and the genetic organization of its antibiotic resistance gene clusters.


METHODS
The S. enterica strains were isolated from humans in France in 2003 and 2004. Antibiotic susceptibility tests and various molecular techniques were used for detection and characterization of SGI1.


RESULTS
We identified SGI1 integrated in the 3' end of the chromosomal thdF gene in six multidrug-resistant serovar Haifa and Newport strains. Two strains, of serovar Haifa and Newport, harboured the previously described SGI1-H variant. A new variant of the novel SGI1-Ks group, named SGI1-K6, revealed IS26-mediated rearrangements of the antibiotic resistance gene cluster in two serovar Newport strains. Two other serovar Newport strains harboured the SGI1-L complex class 1 integron containing the dfrA15 and bla(PSE-1) resistance gene cassettes. In addition, these variants of SGI1 also contained large IS26-composite transposons inserted by a transposition event in the SGI1 backbone. These IS26-composite transposons showed a similar genetic structure to the SGI1-K variants containing an In4-type integron, a mercury resistance operon and parts of Tn1721 and Tn5393. These extended resistance gene clusters containing up to 10 antibiotic resistance genes were named SGI1-L1 and -L2.


CONCLUSIONS
The serovar Haifa represents the 16th S. enterica serovar in which SGI1 has been identified. The genomic island SGI1 appears to be a hotspot of acquisition of antibiotic resistance genes by the transposition of In4-type integrons and large IS26-composite transposons.
Doublet
Benoît
B
Institut Pasteur, Centre National de Référence des Salmonella, Laboratoire des Bactéries Pathogènes Entériques, 28 rue du Docteur Roux, 75724 Paris Cedex 15, France. benoit.doublet@tours.inra.fr
Praud
Karine
K
Weill
François-Xavier
FX
Cloeckaert
Axel
A
D000900:Anti-Bacterial Agents / Q000494:pharmacology; D004251:DNA Transposable Elements; D004269:DNA, Bacterial / Q000737:chemistry / Q000235:genetics; D024901:Drug Resistance, Multiple, Bacterial; D005602:France; D015321:Gene Rearrangement; D005798:Genes, Bacterial; D044404:Genomic Islands; D006801:Humans; D032023:Integrons; D008826:Microbial Sensitivity Tests; D008969:Molecular Sequence Data; D005810:Multigene Family; D011995:Recombination, Genetic; D012480:Salmonella Infections / Q000382:microbiology; D019779:Salmonella enterica / Q000187:drug effects* / Q000235:genetics*; D017422:Sequence Analysis, DNA
D000900:Anti-Bacterial Agents; D004251:DNA Transposable Elements; D004269:DNA, Bacterial