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

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 beta-lactamases (ESBLs) and members of the clinically important O25b:H4-ST131 lineage. 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 (TM) 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. 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 x 10(4)/100 mL and 30 ciprofloxacin-resistant colonies were isolated. Twenty of the 30 colonies belonged to clone ST131; 10 of these had bla(CTX-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. 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.