MOLECULAR APPROACHES FOR THE IDENTIFICATION AND CHARACTERIZATION OF ANTIMICROBIAL RESISTANCE IN FOODBORNE PATHOGENS
Location: Bacterial Epidemiology and Antimicrobial Resistance
Title: Analysis and comparison of antimicrobial resistance mechanisms and plasmids found in multi-drug resistant (MDR) Salmonella enterica and Escherichia coli
Submitted to: American Society for Microbiology General Meeting
Publication Type: Abstract Only
Publication Acceptance Date: March 8, 2012
Publication Date: June 16, 2012
Citation: Frye, J.G., Hiott, L.M., Barrett, J.B., Glenn, L.M., Englen, M.D., Jackson, C.R. 2012. Analysis and comparison of antimicrobial resistance mechanisms and plasmids found in multi-drug resistant (MDR) Salmonella enterica and Escherichia coli. American Society for Microbiology 112th General Meeting, June 16-19, 2012, San Francisco, California. p. 143.
Background: Salmonella enterica and Escherichia coli are often isolated from food animals and can be multi drug resistant (MDR). While both Salmonella and E. coli can potentially be transmitted to humans via animal food products, Salmonella may cause MDR infections in humans, and E. coli may serve as a reservoir for resistance genes that can be transferred to other bacteria as reported in the literature. We studied the resistance genes and genetic elements that may be mobilized during transfer.
Methods: 33 MDR Salmonella and 30 E. coli isolated from healthy food animals at slaughter were screened by multiplex polymerase chain reaction (PCR) for 18 plasmid replicon types. The isolates were further screened by DNA microarray analysis for 1,269 resistance and plasmid genes. Plasmids from ten isolates of each species with similar plasmid and antimicrobial resistance genes detected were sequenced using 454 technology.
Results: Multiple alleles of resistance genes were found, such as blaCMY-2, blaTEM-1, floR, aac(3), aadA, aphA1, strBA, sulI, sulII, dfrA, dhf, tet(A)(B)(C)(D), and tetR. Plasmid backbone genes were homologous to replication, maintenance, and conjugative transfer genes found in several plasmid replicon groups. Assembled contiguous sequences (up to 30,000 bp long) were up to 100% homologous to antimicrobial resistance and virulence plasmids found in the National Center for Biotechnology Information (NCBI) database. These included members of the IncA/C, I1, HI1, F, and P plasmid replicon types. Comparison of plasmid sequences between species identified several highly homologous regions in common, especially in IncA/C plasmid. The analysis also identified some genetic elements unique to each, indicating that there is also variability within Salmonella and E. coli MDR plasmids.
Conclusions: These data demonstrate that some plasmids carrying resistance genes in Salmonella and E. coli are highly homologous, suggesting a common ancestry. Other plasmids demonstrate diversity in their replicon types, gene content, sequence and overall structure. Sequence analysis of these MDR plasmids improves our understanding of the genetic mechanisms responsible for MDR and its possible transfer between Salmonella and E. coli in animals.