Mobilization of qnrB2 and ISCR1 in plasmids

Abstract

The DNA sequences of two IncHI2 plasmids, pEC-IMP and pEC-IMPQ, from metallo-beta-lactamase-producing Enterobacter cloacae clinical isolates were determined. The two conjugative plasmids are almost identical, but pEC-IMPQ carries an additional segment containing an orf513 (ISCR1), a truncated 3' conserved sequence, and a qnrB2. Comparative analyses provide support for the proposed ISCR1-mediated gene mobilization.

FIG. 1.

(a) Schematic diagram of the plasmids pEC-IMPQ and pEC-IMP. The qnrB2-containing region in pEC-IMPQ is depicted in a white box. The inversion is indicated by dotted lines. The five nucleotide substitutions are indicated by black arrowheads. The four class 1 integrons are depicted in gray boxes. The other features indicated are as follows: repHIA and repHI2, replication origins; ter, tellurite resistance gene cluster; pbr, lead resistance gene cluster; mer, mercury resistance gene cluster; ars, arsenic resistance gene cluster; aph, putative aminoglycoside phosphotransferase gene; ereA2*, erythromycin esterase pseudogene; and arr, putative rifampin ADP-ribosyl transferase gene. The ISCR1-containing regions are detailed in panel b. (b) The genetic contexts near the extra region found in pEC-IMPQ. The repeats of the redundant ISCR1 in pEC-IMPQ are marked. The dotted line indicates the 5.8-kb region identical to a previously reported plasmid from a Salmonella enterica serovar Keurmassar. The proposed circular intermediate of an aberrant RC replication carrying the qnrB2-truncated qacEΔ1-sul1 is shown above. The proposed integration event between this intermediate and pEC-IMP are marked (the big ×). The intI1 integrase genes of the class 1 integrons are crosshatched. The resistance genes that comobilized with the ISCR1 are shown in gray. Other resistance genes are shown in white. The single nucleotide differences of the sul1 genes are indicated (T and A) at the positions of variation. Truncated orf genes are marked with an asterisk after the gene name. The str genes encode streptomycin resistance proteins.