Molecular Characterisation of Plasmids Encoding blaCTX-M from Faecal Escherichia coli in Travellers Returning to the UK from South Asia.

BACKGROUND The global prevalence of ESBL-producing Escherichia coli is rising and is dominated by blaCTX-M spread by plasmids. Travellers to South Asia from Western Europe have high rates of acquisition of faecal CTX-M-producing E. coli (CTX-M-EC). AIMS We aimed to determine the conjugative ability of CTX-M-EC acquired by healthy volunteers after travel to South Asia, the proportion of travel-acquired CTX-M-EC where blaCTX-M is encoded on a plasmid versus on the bacterial chromosome, and the relatedness of travel-acquired CTX-M-EC plasmids to previously sequenced plasmids. METHODS Faecal samples were collected pre- and post-travel from 23 volunteers who visited South Asia, and the CTX-M-EC were cultured. After short- and long-read sequencing, ten plasmid sequences were identified and compared to previously sequenced plasmids in Genbank. Conjugation to E. coli K-12 was undertaken using filter mating. FINDINGS 35% of CTX-M-EC isolates tested transferred the blaCTX-M plasmid by conjugation. Travel-acquired CTX-M-EC carried blaCTX-M on a plasmid in 62% of isolates, whereas 38% of isolates had blaCTX-M on the chromosome. CTX-M-EC plasmids acquired after travel to South Asia have close homology to previously described epidemic plasmids which are widely disseminated in humans, animals, and the natural environment. CONCLUSION Globally successful epidemic plasmids are involved in the spread of CTX-M-EC. Targeted strategies may be used to displace such plasmids from the host strain as part of efforts in infection prevention and control in healthcare settings. Bacteria with blaCTX-M plasmids were readily acquired by healthy volunteers and were carried on return to the UK, providing opportunities for onward dissemination.