title: Characterization of Salmonella enterica serovar Typhimurium isolates harboring a chromosomally encoded CMY-2 beta-lactamase gene located on a multidrug resistance genomic island.
abstract: Since 2004, extended-spectrum cephalosporin (ESC)-resistant Salmonella enterica serovar Typhimurium (S. Typhimurium) isolates have been detected from cattle in the northern major island of Japan, Hokkaido. Resistance to ESCs was found to be mediated by CMY-2 type β-lactamase among 22 epidemiologically unrelated isolates showing indistinguishable pulsed-field gel electrophoresis patterns. Southern blot analysis using I-CeuI-digested genomic DNA demonstrated that the CMY-2 β-lactamase gene (bla(CMY-2)) was integrated in a 2.5-Mb chromosomal fragment. Genetic analysis of S. Typhimurium isolate L-3553 indicated that bla(CMY-2) was located on a unique 125-kb genomic island, GI-VII-6, which consists of 140 open reading frames. Pairwise alignment of GI-VII-6 and Escherichia coli plasmid pAR060302 (size, 167 kb) revealed that a large proportion of GI-VII-6 (99%) shows a high sequence similarity (>99%) with pAR060302. GI-VII-6 contains 11 antimicrobial resistance genes including sul1, qacEΔ1, aadA2, and dfrA12 in the aadA2 region; sugE1 and bla(CMY-2) in the bla(CMY-2) region; and sul2, strA, strB, tet(A), and floR in the floR region. Two directly repeated IS26 copies were present at both ends of GI-VII-6. Junction regions of GI-VII-6 were flanked by an 8-bp direct repeat, indicating that GI-VII-6 was acquired by transposition involving IS26 transposase. PCR scanning revealed that the overall structure of GI-VII-6 was almost identical in the 22 isolates. Phylogenetic analysis suggested that S. Typhimurium isolates harboring GI-VII-6 belong to a different genomic lineage than other whole-genome-sequenced S. Typhimurium strains. These data indicate that a particular clone of S. Typhimurium harboring GI-VII-6 has spread among the cattle population in Hokkaido, Japan.
authors.affiliation: Safety Research Team, National Institute of Animal Health, 3-1-5 Kannondai, Tsukuba, Ibaraki 305-0856, Japan.
authors.forename: Francis
authors.initials: F
authors.lastname: Shahada
authors.forename: Tsuyoshi
authors.initials: T
authors.lastname: Sekizuka
authors.forename: Makoto
authors.initials: M
authors.lastname: Kuroda
authors.forename: Masahiro
authors.initials: M
authors.lastname: Kusumoto
authors.forename: Daiki
authors.initials: D
authors.lastname: Ohishi
authors.forename: Atsuko
authors.initials: A
authors.lastname: Matsumoto
authors.forename: Hizuru
authors.initials: H
authors.lastname: Okazaki
authors.forename: Kiyoshi
authors.initials: K
authors.lastname: Tanaka
authors.forename: Ikuo
authors.initials: I
authors.lastname: Uchida
authors.forename: Hidemasa
authors.initials: H
authors.lastname: Izumiya
authors.forename: Haruo
authors.initials: H
authors.lastname: Watanabe
authors.forename: Yukino
authors.initials: Y
authors.lastname: Tamamura
authors.forename: Taketoshi
authors.initials: T
authors.lastname: Iwata
authors.forename: Masato
authors.initials: M
authors.lastname: Akiba
mesh_terms: D000818:Animals; D000900:Anti-Bacterial Agents / Q000494:pharmacology; D015139:Blotting, Southern; D002417:Cattle; D002876:Chromosomes, Bacterial / Q000235:genetics*; D024901:Drug Resistance, Multiple, Bacterial / Q000235:genetics*; D044404:Genomic Islands / Q000235:genetics*; D010802:Phylogeny; D010957:Plasmids / Q000235:genetics; D016133:Polymerase Chain Reaction; D012486:Salmonella typhimurium / Q000187:drug effects / Q000235:genetics*; D001618:beta-Lactamases / Q000145:classification / Q000235:genetics*
chemical_list: D000900:Anti-Bacterial Agents; C103022:beta-lactamase CMY-2; D001618:beta-Lactamases