Submitted to: Plasmid Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/8/2011
Publication Date: 4/11/2011
Citation: Chen, C., Strobaugh Jr, T.P., Lindsey, R.L., Frye, J.G., Uhlich, G.A. 2011. Sequence analysis of a group of low molecular-weight plasmids carrying multiple IS903 elements flanking a kanamycin resistance aph gene in Salmonella enterica serovars. Plasmid Journal. 65:246-252.
Interpretive Summary: Foodborne bacterial pathogens that are resistant to multiple antibiotics pose serious public and animal health concerns. The antibiotic resistance genes often reside on mobile genetic elements such as plasmids (circular DNA molecules), bacteriophages (viruses that infect bacteria), and transposable elements (DNA fragments that are able to move from one DNA site to another). A group of small (< 9000 base pairs) plasmids carrying genes responsible for kanamycin resistance in three different Salmonella serovars were characterized. DNA sequence results showed that they were nearly identical, suggesting that they were closely related. This study will increase our understanding of antibiotic resistance gene transfer between bacteria, thus enabling us to design effective strategies to prevent the dissemination of resistance genes and plasmids.
Technical Abstract: A group of low molecular-weight ColE1-like plasmids carrying the aph sequence type aph(ii), from three different Salmonella serovars were sequenced. These plasmids carry 2 or more copies of IS903 elements, with up to 21 bp sequence differences to one another, two of which flank the aph gene. This group of plasmids did not appear to carry any known mobilization genes and instead carry three open reading frames encoding hypothetical proteins of unknown function possibly organized in an operon. The plasmid replication region (RNA I/II - rom) of this plasmid group showed extensive homology to that of pKPN2 of Klebsiella pneumoniae and pCol-let of E. coli. Three plasmids had identical sequences, and the fourth had an extra copy of IS903 with target duplication, suggesting a recent divergence in the different serovars from a common ancestor. These data indicate that this group of ColE1-like plasmids may have been horizontally transferred into Salmonella enterica from K. pneumoniae, where they have become widespread in different Salmonella serovars and have begun to diverge.