Insertion Sequence IS Ecp1B Is Involved in Expression and Mobilization of a bla CTX-M β-Lactamase Gene

Abstract

ABSTRACT The genetic structures (ca. 10-kb DNA fragment) surrounding the plasmid-borne extended-spectrum β-lactamase bla CTX-M-19 gene in a Klebsiella pneumoniae clinical isolate were determined. This β-lactamase gene was part of a 4,797-bp transposon inserted inside orf1 of Tn 1721. Inside this transposon, bla CTX-M-19 was bracketed upstream and downstream by insertion sequences IS E cp1B and IS 903D, respectively, and further downstream by a truncated gene encoding an outer membrane protein for iron transport. The single-copy IS Ecp1B 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 IS E cp1B and a second sequence farther away, resembling its second inverted repeat. Additionally, IS Ecp1B 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 IS Ecp1 -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 IS Ecp1 -like elements to mobilize and to promote the expression of β-lactamase genes may explain, in part, the current spread of CTX-M-type enzymes worldwide.