Multilocus sequence typing of IncN plasmids

OBJECTIVES: Incompatibility group N (IncN) plasmids have been associated with the dissemination of antimicrobial resistance and are a major vehicle for the spread of blaVIM-1 in humans and blaCTX-M-1 in animals. A plasmid multilocus sequence typing (pMLST) scheme was developed for rapid categorization of IncN plasmids.

METHODS: Twelve fully sequenced IncN plasmids available at GenBank were analysed in silico for selecting the loci for the IncN-specific pMLST. A total of 58 plasmids originating from different reservoirs (human, pig, poultry, cattle and horses) and geographic regions (Italy, Greece, Denmark, UK and The Netherlands) were classified by DNA sequencing of the amplicons obtained for the repA, traJ and korA loci.

RESULTS: Eleven sequence types (STs) were defined on the basis of allele sequences of the three selected loci. Most plasmids carrying blaCTX-M-1 (24/27) isolated in different countries from both animals and humans belonged to ST1, suggesting dissemination of an epidemic plasmid through the food chain.

Fifteen of 17 plasmids carrying blaVIM-1 from Klebsiella pneumoniae and Escherichia coli, isolated during a 5year period in Greece were assigned to ST10, suggesting that spread and persistence of this particular IncN-carrying blaVIM-1 lineage in Greece. CONCLUSIONS: This study proposes the use of pMLST as a suitable and rapid method for identification of IncN epidemic plasmid lineages.

The recent spread of blaCTX-M-1 among humans and animals seems to be associated with the dissemination of an epidemic IncN plasmid lineage.