Cullik A, Pfeifer Y, Prager R, von Baum H, Witte W (2010): A novel IS26 structure is surrounding blaCTX-M genes in different plasmids of German clinical isolates of Escherichia coli
J. Med. Microbiol. 59 (5): 580-587. Epub Jan 21. doi:10.1099/jmm.0.016188-0.

This report focuses on the molecular characterization of 22 extended-spectrum beta-lactamase (ESBL) producing E. coli isolates collected in a German university hospital, during a period of nine months in 2006. Relationship analysis of clinical isolates was done via pulsed-field gel-electrophoresis, mulit-locus sequence typing, plasmid profiling and additionally PCR for bla_ESBL detection and phylogroups. After conjugal transfer plasmid isolation and subsequent PCR for bla_ESBL detection and 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) as 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) as well as one new type CTX-M-65 (n=1). In 18 isolates bla_ESBL genes were located on conjugative plasmids in sizes between 40 and 180 kbp belonging to incompatibility groups FII (n=9), N (n=5) andI1 (n=4). Thereby bla_CTX-M were found to be associated with the commonly known 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 composition that have not been described yet. The results reveal the emergence of bla_ESBL, preferentially bla_CTX-M, located on different plasmids harboured by genotypic different E. coli strains. The identical gene arrangement in 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.