Title: Distribution of ColE1-like KAN-resistance plasmids in a population of Salmonella enterica from animal diagnostic samples Authors
Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: March 3, 2010
Publication Date: May 23, 2010
Citation: Chen, C., Lindsey, R.L., Strobaugh Jr, T.P., Frye, J.G., Meinersmann, R.J. 2010. Distribution of ColE1-like KAN-resistance plasmids in a population of Salmonella enterica from animal diagnostic samples [abstract]. 1:1. Technical Abstract: Background: Previous studies showed that some Salmonella isolates may harbor ColE1-like plasmids that carry a single aph gene responsible for kanamycin resistance (KAN-R). However the distribution of these plasmids is unknown. Methods: KAN-R Salmonella isolates (n=102) collected through the 2005 National Antimicrobial Resistance Monitoring System (NARMS) were screened by PCR using 2 ColE1 primer sets. Plasmids from ColE+ isolates were transformed into E. coli DH5alpha and characterized by restriction mapping and sequencing. Nucleotide and amino acid sequence similarity was determined using BLAST against NCBI GenBank. Linkage disequilibrium (LD) was calculated using ARLEQUIN. Results: Thirty of the 102 KAN-R Salmonella isolates screened were PCR positive for ColE1; KAN-R ColE1-like plasmids from 23 isolates propagated in E. coli. All KAN-R ColE+ isolates carried the aph(3’)-I gene encoding an aminoglycoside phosphotransferase. Restriction mapping and sequencing revealed three major plasmid groups, two of which were similar to previously sequenced KAN-R ColE1 plasmids pU302S (group A, 47.8% of the 23 plasmids) and pSN11/00Kan (group B, 30.4%), and a novel sequence group (group C, 21.7%). The aph genes in group A and B plasmids were identical, and the aph gene in the novel group C plasmids differed by 11 nucleotides resulting in 4 amino acid changes. Group A plasmids were found in serotypes Typhimurium (6) and Newport (5) isolated from a variety of sources; group B plasmids were distributed mainly in Newport (5) and Heidelberg (2); group C plasmids were in Typhimurium (1), Newport (3), and Bardo (1), all isolated from cattle/dairy cattle. Pairwise LD between the ColE1 plasmid groups showed linkage (P value of 0.05) to DT104 and the aph sequence. Conclusion: The KAN-R ColE1-like plasmids were widely spread among different Salmonella serotypes and sources, and appear to have come from different lineages. Due to their high copy number and mobility, monitoring of this plasmid group illustrates an important mechanism of transmission of antimicrobial resistance genes.