Chromosomally Encoded bla CMY-2 Located on a Novel SXT/R391-Related Integrating Conjugative Element in a Proteus mirabilis Clinical Isolate

Abstract

ABSTRACT Integrating conjugative elements (ICEs) are mobile genetic elements that can transfer from the chromosome of a host to the chromosome of a new host through the process of excision, conjugation, and integration. Although SXT/R391-related ICEs, originally demonstrated in Vibrio cholerae O139 isolates, have become prevalent among V. cholerae isolates in Asia, the prevalence of the ICEs among Gram-negative bacteria other than Vibrio spp. remains unknown. In addition, SXT/R391-related ICEs carrying genes conferring resistance to extended-spectrum cephalosporins have never been described. Here we carried out a genetic analysis of a cefoxitin-resistant Proteus mirabilis clinical isolate, TUM4660, which revealed the presence of a novel SXT/R391-related ICE, ICE Pmi Jpn1. ICE Pmi Jpn1 had a core genetic structure showing high similarity to that of R391 and carried xis and int genes completely identical to those of R391, while an IS 10 -mediated composite transposon carrying bla CMY-2 was integrated into the ICE. A nucleotide sequence identical to the 3′ part of IS Ecp1 was located upstream of the bla CMY-2 gene, and other genes observed around bla CMY-2 in earlier studies were also present. Furthermore, the nucleotide sequences of hot spot 2 and hot spot 4 in ICE Pmi Jpn1 showed high similarity to that of hot spot 2 in SXT MO10 and with a part of the nucleotide sequence found in P. mirabilis ATCC 29906, respectively. ICE Pmi Jpn1 was successfully transferred to Escherichia coli , Klebsiella pneumoniae , Salmonella enterica serovar Typhimurium, and Citrobacter koseri in conjugation experiments. These observations suggest that ICEs may contribute to the dissemination of antimicrobial resistance genes among clinically relevant Enterobacteriaceae , which warrants careful observation of the prevalence of ICEs, including SXT/R391-related ICEs.