A novel IS26 structure is surrounding blaCTX-M genes in different plasmids of German clinical isolates of Escherichia coli

Abstract

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 blaESBL detection and phylogroups. After conjugal transfer plasmid isolation and subsequent PCR for blaESBL detection and incompatibility groups were performed. Using one-primer-walking, up to 3600 bp upstream and downstream of different blaCTX-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 blaESBL 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 blaCTX-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 blaCTX-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 blaESBL, preferentially blaCTX-M, located on different plasmids harboured by genotypic different E. coli strains. The identical gene arrangement in blaCTX-M neighbourhood in plasmids of different incompatibility groups indicates a main role of IS26 in distribution of mobile resistance elements between different plasmids.