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

The global prevalence of ESBL-producing E. coli is rising and is dominated by blaCTX-M spread by plasmids. Travelers to South Asia from Western Europe have high rates of acquisition of CTX-M-producing E. coli (CTX-M-EC). We determined the proportion of travel-acquired CTX-M-EC strains where blaCTX-M is encoded on a plasmid compared to the bacterial chromosome, the relatedness of acquired plasmids to previously sequenced plasmids and their in vitro conjugative ability. Faecal samples were collected pre and post-travel from twenty-three volunteers who visited South Asia, and CTX-M-EC were cultured. After short and long-read sequencing, ten plasmid sequences were identified using a hybrid assembly. BLAST, RAST, and BRIG were used to identify and characterise plasmids, and to generate plasmid sequence comparisons. Conjugation to E. coli K-12 was undertaken using filter mating and confirmed using CTX-M multiplex PCR and PFGE.Contigs including a blaCTX-M ORF were identified as of plasmid-origin in 17/30 (57%), chromosomal in 11/30 (37%), or origin indistinguishable in 2/30 (6%).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. Travel-acquired plasmids either contained the classical transfer operon (80%) or were bacteriophage-like plasmids (20%). CTX-M-EC transferred the blaCTX-M plasmid by conjugation in 5/11 volunteer E. coli tested (45%). Globally successful epidemic plasmids are involved in the spread of CTX-M-EC. Bacteria with such plasmids were readily acquired by healthy volunteers and were carried on return to the UK, providing opportunities for onward dissemination.