Molecular epidemiology of fluoroquinolone-resistant ST131 Escherichia coli producing CTX-M extended-spectrum beta-lactamases in nursing homes in Belfast, UK.

Objectives: Between January 2004 and May 2006 Escherichia coli producing extended-spectrum β-lactamases (ESBLs) were isolated from the faeces of 118/294 residents from 16 nursing homes in Belfast. Of these, 58 isolates belonged to UK strain A, a variant of the international ST131 clone. Here we investigated the remaining 60 ESBL producers.

Methods: MICs were determined and interpreted using BSAC methodology. Isolates were characterized by phylogenetic typing, real-time PCR and PFGE. Plasmids were rep typed by PCR and their similarity to IncI1 reference plasmid pEK204 was investigated by restriction fragment length polymorphism analysis. The molecular environments surrounding bla(CTX-M) were determined by DNA sequencing and PCR.

Results: Fifty-nine of 60 isolates belonged to the B2, ST131 lineage; of these 28 belonged to the previously defined UK strain C, while the other 31 were clustered into five groups by PFGE. Forty-nine isolates harboured bla(CTX-M-3) on plasmids of five different rep types (I1, FIA, FIA-FIB, N and Y) and 11 harboured bla(CTX-M-15) on F-type plasmids (FIA and FIA-FIB). All CTX-M-3 ESBL producers and three with CTX-M-15 ESBL had an intact copy of ISEcp1 immediately upstream of bla(CTX-M); the remaining eight with CTX-M-15 ESBL had a truncated ISEcp1.

Conclusions: Gut colonization among nursing home residents in Belfast with ciprofloxacin-resistant E. coli producing ESBLs almost entirely involves clonal spread of ST131 variants, with similar genetic environments for bla(CTX-M-3) or bla(CTX-M-15) as in pEK204 and pEK499. Such diversity indicates dissemination of both plasmids and ESBL genes among a single commonly multiresistant clone.