Chromosomal Integration of the Extended-Spectrum β-Lactamase Gene bla CTX-M-15 in Salmonella enterica Serotype Concord Isolates from Internationally Adopted Children

Abstract

ABSTRACT We report the emergence of Salmonella enterica isolates of serotype Concord (and its monophasic variant 6,7:l,v:-) producing the extended-spectrum β-lactamases (ESBLs) SHV-12 and CTX-M-15 in France and Norway between 2001 and 2006 (43 in France and 26 in Norway). The majority of these isolates were from adopted children from Ethiopia, most of whom were healthy carriers. Several symptomatic secondary cases were found in the adoptive families and health care facilities in France. Serotype Concord isolates collected before 2003 produced SHV-12 encoded on a 340-kb conjugative plasmid of replicon IncI1. Isolates collected after 2003 produced CTX-M-15. We detected two conjugative plasmids carrying bla CTX-M-15 . One plasmid, approximately 300 kb in size, was positive for the IncHI2 replicon and the plasmid-mediated quinolone resistance gene qnrA1 . The other plasmid, from one of the earliest CTX-M-15-producing isolates collected, was a fusion plasmid with IncY and IncA/C 2 replicons and was 200 kb in size. However, we showed, using Southern hybridization of I-CeuI-digested chromosomal DNA and S1 nuclease analysis of plasmid DNA, that most isolates had a bla CTX-M-15 gene located on chromosomal DNA. Analysis of the flanking regions of the chromosomally located bla CTX-M-15 gene by cloning revealed an IS Ecp1 truncated by an intact IS 26 upstream from the bla CTX-M-15 gene and a truncated orf477 gene downstream from bla CTX-M-15 . We found regions beyond the IS 26 and the orf477 genes that were derived from IncA/C 2 plasmids, suggesting the chromosomal integration of part of the bla CTX-M-15 -carrying IncY and IncA/C 2 fusion plasmid from early CTX-M-15-producing isolates.