Isolation of fluoroquinolone-resistant O25b:H4-ST131 Escherichia coli with CTX-M-14 extended-spectrum β-lactamase from UK river water

Objectives: We analysed water sampled from the River Thames in London for Escherichia coli resistant to oxyimino-cephalosporins and/or fluoroquinolones, particularly seeking isolates with CTX-M extended-spectrum β-lactamases (ESBLs) and members of the clinically important O25b:H4-ST131 lineage. Methods: River water was collected from three urban sites on the River Thames by the City of London Port Health Authority on two occasions 1 week apart. Coliforms and E. coli were identified by the Quanti-Tray™ method. Disc susceptibility tests were performed and MICs were determined for E. coli isolates resistant to either ciprofloxacin or cefpodoxime and genetic relatedness was determined by PFGE and real-time PCR. PCR was used for phylogenetic and plasmid typing, to detect antibiotic resistance genes and to detect ISEcp1 upstream of bla_CTX-M genes. bla_CTX-M alleles were identified by sequencing. Results: The mean E. coli count, as the most probable number, from the first river samples, taken on a falling tide on 23 March 2010, was 4.7×10⁴/100 mL and 30 ciprofloxacin-resistant colonies were isolated. Twenty of the 30 colonies belonged to clone ST131; 10 of these had blaCTX-M-14 whereas the remaining 10 lacked ESBLs. The ST131 isolates represented two different PFGE types. No ciprofloxacin-or cefpodoxime-resistant E. coli were isolated from the second river sample taken at low tide. CTX-M-15, the most common ESBL in clinical E. coli, was not detected in the river samples. Conclusions: Water from the River Thames in West London is contaminated, perhaps transiently, with antibiotic-resistant E. coli belonging to the clinically important O25b:H4-ST131 lineage.