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Volume 7, Number 3—June 2001

Dispatch

Expanding Drug Resistance through Integron Acquisition by IncFI Plasmids of Salmonella enterica Typhimurium

Alessandra Carattoli*Comments to Author , Laura Villa*, Cristina Pezzella*, Eugenio Bordi†, and Paolo Visca†‡
Author affiliations: *Istituto Superiore di Sanità, Rome, Italy; †National Institute for Infectious Diseases Lazzaro Spallanzani, Rome, Italy; ‡Università di Roma Tre, Rome, Italy

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Figure 1

Structural organization of integrons carried by IncFI plasmids. Numbers above each lane indicate plasmid reference numbers as defined (Table). Lane C shows the plasmidless E. oli K-12 strain CSH26 (11). A: agarose (0.8%) gel electrophoresis in 1x Tris-borate-EDTA buffer of plasmid DNA extracted from E. coli K-12 exconjugants. DNA was stained with ethidium bromide and visualized under UV light. B: Southern blot hybridization of plasmids shown in panel A with the intI1 probe. C: Southern blot hybr

Figure 1. . Structural organization of integrons carried by IncFI plasmids. Numbers above each lane indicate plasmid reference numbers as defined (Table). Lane C shows the plasmidless E. oli K-12 strain CSH26 (11). A: agarose (0.8%) gel electrophoresis in 1x Tris-borate-EDTA buffer of plasmid DNA extracted from E. coli K-12 exconjugants. DNA was stained with ethidium bromide and visualized under UV light. B: Southern blot hybridization of plasmids shown in panel A with the intI1 probe. C: Southern blot hybridization with the intI1 probe of PvuII-BamHI double-digested DNA from E. coli K-12 exconjugants. The DNA was extracted as described (7). The intI1 probe was amplified with primers corresponding to nt 4680-4700 and nt 5252-5232 of the released Tn21 sequence (GenEMBL accession no. AF071413). Plasmid pACYC184::Tn21 (10) was used as the template. The probe was labeled with [-32P]dCTP by using a random priming kit (GibcoBRL). Chromosomal DNA fluoresced because of weak trapping of partially degraded plasmids. D: schematic representation of In-t2 and In-t1 integrons. The thick bars above each structure represent the DNA fragments recognized by the intI1 probe. The 4.0-kb PvuII-BamHI fragment (In-t2) encompasses the intI1 gene segment downstream of the conserved PvuII site (0.6 kb), the oxa1 and aadA1 gene cassettes (2.2 kb), and the 3'-CS comprising the sul1 gene upstream of the BamHI site (1.2 kb) (7,8). The 1.2-kb PvuII-BamHI fragment (In-t1) encompasses the intI1 gene segment and part of the aadB gene cassette (7).

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