Insertion sequence ISEcp1B is involved in expression and mobilization of a bla(CTX-M) beta-lactamase gene.
The genetic structures (ca. 10-kb DNA fragment) surrounding the plasmid-borne extended-spectrum beta-lactamase bla(CTX-M-19) gene in a Klebsiella pneumoniae clinical isolate were determined. This beta-lactamase gene was part of a 4,797-bp transposon inserted inside orf1 of Tn1721. Inside this transposon, bla(CTX-M-19) was bracketed upstream and downstream by insertion sequences ISE cp1B and IS903D, respectively, and further downstream by a truncated gene encoding an outer membrane protein for iron transport. The single-copy ISEcp1B element was probably involved alone in the mobilization process that led to a 5-bp duplication at the target site of the transposed fragment. This mobilization event probably involved one inverted repeat of ISE cp1B and a second sequence farther away, resembling its second inverted repeat. Additionally, ISEcp1B provided -35 and -10 promoter sequences, contributing to the high-level expression of the bla(CTX-M-19) gene. Southern blot analysis failed to identify a reservoir of ISEcp1-like sequences among a series of gram-negative and gram-positive bacterial species usually found in the skin and intestinal human floras. The ability of ISEcp1-like elements to mobilize and to promote the expression of beta-lactamase genes may explain, in part, the current spread of CTX-M-type enzymes worldwide.
Poirel
Laurent
L
Service de Bactériologie-Virologie, Hôpital de Bicêtre, Assistance Publique/Hôpitaux de Paris, Faculté de Médecine Paris-Sud, 94275 Le Kremlin Bicêtre cedex, France.
Decousser
Jean-Winoc
JW
Nordmann
Patrice
P
D000900:Anti-Bacterial Agents / Q000494:pharmacology; D001483:Base Sequence; D003001:Cloning, Molecular; D004251:DNA Transposable Elements / Q000235:genetics*; D015964:Gene Expression Regulation, Bacterial / Q000235:genetics*; D015971:Gene Expression Regulation, Enzymologic / Q000235:genetics*; D006090:Gram-Negative Bacteria / Q000201:enzymology / Q000235:genetics; D006094:Gram-Positive Bacteria / Q000201:enzymology / Q000235:genetics; D017403:In Situ Hybridization; D007711:Klebsiella pneumoniae / Q000201:enzymology* / Q000235:genetics*; D008826:Microbial Sensitivity Tests; D008969:Molecular Sequence Data; D010957:Plasmids / Q000235:genetics; D012329:RNA, Bacterial / Q000096:biosynthesis; D020133:Reverse Transcriptase Polymerase Chain Reaction; D001618:beta-Lactamases / Q000235:genetics*
D000900:Anti-Bacterial Agents; D004251:DNA Transposable Elements; D012329:RNA, Bacterial; D001618:beta-Lactamases