Expansion of the IncX plasmid family for improved identification and typing of novel plasmids in drug-resistant Enterobacteriaceae

Timothy J. Johnson, Eliza M. Bielak, Daniela Fortini, Lars Hestbjerg Hansen, Henrik Hasman, Chitrita Debroy, Lisa K. Nolan, Alessandra Carattoli

Research output: Contribution to journalArticlepeer-review

220 Scopus citations


IncX plasmids are narrow host range plasmids of Enterobactericeae that have been isolated for over 50. years. They are known to encode type IV fimbriae enabling their own conjugative transfer, and to provide accessory functions to their host bacteria such as resistance towards antimicrobial agents and biofilm formation. Previous plasmid-based replicon typing procedures have indicated that the prevalence of IncX plasmids is low among members of the Enterobacteriaceae. However, examination of a number of IncX-like plasmid sequences and their occurrence in various organisms suggests that IncX plasmid diversity and prevalence is underappreciated. To address these possible shortcomings, we generated additional plasmid sequences of IncX plasmids of interest and compared them to the genomes of all sequenced IncX-like plasmids. These comparisons revealed that IncX plasmids possess a highly syntenic plasmid backbone, but that they are quite divergent with respect to nucleotide and amino acid similarity. Based on phylogenetic comparisons of the sequenced IncX plasmids, the IncX plasmid group has been expanded to include at least four subtypes, IncX1-IncX4. A revised IncX plasmid replicon typing procedure, based upon these sequences and subtypes, was then developed. Use of this revised typing procedure revealed that IncX plasmid occurrence among bacterial populations is much more common than had previously been acknowledged. Thus, this revised procedure can be used to better discern the occurrence of IncX type plasmids among enterobacterial populations.

Original languageEnglish (US)
Pages (from-to)43-50
Number of pages8
Issue number1
StatePublished - Jul 2012

Bibliographical note

Funding Information:
The authors wish to thank the University of Minnesota Veterinary Diagnostic Laboratory and Simone Oliveira for providing strains for this study. This work was carried out in part using computing resources at the University of Minnesota Supercomputing Institute. This work was supported in part by the Minnesota Pork Board (TJJ), National Science Foundation Grant EFO062666 (LKN and TJJ), Italy-USA cooperation project – Italian Ministry of Health Grant DRE 29/12/2010-0001090 (AC), FøSu Grant Number 2101-07-0046 (HH) and by the Dean’s Office in the College of Veterinary Medicine at the University of Minnesota (TJJ).


  • Genomics
  • IncX
  • Plasmid
  • Replicon typing
  • Resistance


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