A novel IS26 structure surrounds blaCTX-M genes in different plasmids from German clinical Escherichia coli isolates

This report focuses on the molecular characterization of 22 extended-spectrum beta-lactamase-producing Escherichia coli isolates collected in a German university hospital during a period of 9 months in 2006. Relationship analysis of clinical isolates was done via PFGE, multilocus sequence typing, plasmid profiling and additionally PCR for bla(ESBL) detection and determination of phylogroups. After conjugal transfer, plasmid isolation and subsequent PCR for bla(ESBL) detection and determination of incompatibility groups were performed. Using one-primer walking, up to 3600 bp upstream and downstream of different bla(CTX-M) genes could be sequenced. beta-Lactamases found were TEM-1 (n=14), SHV-5 (n=1) and a wide variety of CTX-M types (n=21), i.e. CTX-M-15 (n=12), CTX-M-1 (n=4), CTX-M-14 (n=2), CTX-M-9 (n=1), CTX-M-3 (n=1) and one new type, CTX-M-65 (n=1). In 18 isolates, bla(ESBL) genes were located on conjugative plasmids of sizes between 40 and 180 kbp belonging to incompatibility groups FII (n=9), N (n=5) and I1 (n=4). bla(CTX-M) was found to be associated with the common elements ISEcp1, IS26 and IS903-D, but with unusual spacer sequences for ISEcp1 in two isolates. These insertion sequences, connected to bla(CTX-M) as well as other genes, were located between two IS26 elements in a configuration that has not yet been described. The results reveal the emergence of bla(ESBL), predominantly bla(CTX-M), located on different plasmids harboured by genotypically different E. coli strains. The identical gene arrangement in the bla(CTX-M) neighbourhood in plasmids of different incompatibility groups indicates a main role of IS26 in distribution of mobile resistance elements between different plasmids.