Characterization of the genetic environment of bla _ESBL genes, integrons and toxin-antitoxin systems identified on large transferrable plasmids in multi-drug resistant Escherichia coli

摘要

Objectives: Previously 14 conjugative plasmids from multi-drug resistant (MDR) Escherichia coli from healthy humans and food-producing animals in Switzerland were sequenced. The aim of this study was to extend the genetic characterization of these plasmids with a focus on bla _(ESBL)genes including bla _(CTX-M-1)and bla _(TEM), class 1 integrons and toxin-antitoxin (TA) systems contained therein. Methods: The nucleotide sequences and subsequent annotation therein of 14 conjugative plasmids were previously determined from their corresponding transconjugants. The TA loci were confirmed by RASTA-Bacteria. Results: Eight of the conjugative plasmids identified were found to encode genes expressing ESBLs. Structural heterogeneity was noted in the regions flanking both the bla _(CTX-M-1)and bla _(TEM)genes. The bla _(CTX-M-1)genes were associated with the common insertion sequences IS Ecp1 and IS 26 , and uniquely with an IS 5 element in one case; while bla _(TEM)genes were found to be associated with IS 26 and Tn 2 . A new bla _(TEM-210)gene was identified. Seven class 1 integrons were also identified and assigned into 3 groups, denoted as In54, In369 and In501. Sixteen TA loci belonging to 4 of the TA gene families ( relBE , vapBC , ccd and mazEF ) were identified on 11 of these plasmids. Conclusions: Comparative sequence analysis of these plasmids provided data on the structures likely to contribute to sequence diversity associated with these accessory genes, including IS 26 , IS Ecp1 and Tn 2 . All of them contribute to the dissemination of the corresponding resistance genes located on the different plasmids. There appears to be no association between β-lactam encoding genes and TA systems.