The Cassettes and 3′ Conserved Segment of an Integron from Klebsiella oxytoca Plasmid pACM1

Abstract

pACM1 is a conjugative multiresistance plasmid from Klebsiella oxytoca that encodes SHV-5 extended-spectrum β-lactamase (ESBL) and has two integrons. The first is a type I (sul type); the second, detected by hybridization with an intI gene probe, has been putatively identified as a defective type I integron. The cassette region of the first integron has now been fully sequenced and contains three aminoglycoside resistance determinants (aac(6′)-Ib, aac(3)-Ia, and ant(3")-Ia) and two open reading frames of unknown function. In addition, sequencing of a region downstream from the qacEΔ1–sulI–ORF 5 gene cluster of the first integron revealed a copy of insertion sequence IS6100 flanked by inverted copies of sequence from the 11.2-kb insert (In2) of Tn21. This arrangement is similar to that found in In4 of Tn1696. The coincidence of an ESBL gene and mobile elements on a conjugative plasmid has potential implications for the spread of ESBL-mediated drug resistance, though evidence of bla(SHV-5) movement mediated by these elements has not been found.