Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: March 25, 2011
Publication Date: March 25, 2011
Citation: Frye, J.G., Lindsey, R.L., Glenn, L.M., Cray, P.J., Meinersmann, R.J. 2011. Population genetics of multi-drug resistant (MDR) IncA/C plasmid in Salmonella enterica isolated from animals. Bioinformatics and Science Symposium on Population-Level Genetic Diversity. March 25, 2011. Santa Fe, NM. Technical Abstract: Food animals harboring Multi-Drug Resistant (MDR) Salmonella enterica are a potential source for acquisition of zoonotic pathogens. Plasmids (small, self-replicating, extra-chromosomal DNA) are often associated with antimicrobial resistance and plasmids carrying MDR genes have been found to be a major contributor to antimicrobial resistance in Salmonella. The distribution and genetics of these plasmids is under investigation to determine how MDR plasmids develop and are transmitted to Salmonella. In this study a set of 437 Salmonella isolates obtained from clinically ill animals in 2005 were screened for antimicrobial susceptibility to a panel of 17 antimicrobials. The isolates were also assayed for the presence of 18 different plasmids by multiplex PCR analysis. The plasmid type most often detected was IncA/C (26.3%) which was also associated with the MDR Salmonella isolates. Based upon antimicrobial resistance pheontypes, a representative subset of 216 isolates were analyzed by Pulse Field Gel Electrophoresis (PFGE, “fingerprint”) analysis. Cluster analysis based on these PFGE patterns showed that Salmonella positive for IncA/C plasmids grouped together based on serotype and MDR profile. Cluster analysis also revealed that IncA/C plasmids and MDR has been associated with Salmonella previous to the introduction of the therapeutic use of antimicrobials suggesting that the spread of resistance is likely due to the expansion of resistant clones rather than the accretion of new resistances. A subset of 59 of the MDR isolates containing IncA/C plasmids were analyzed by a DNA microarray constructed of probes designed to detect antimicrobial resistance genes (n = 775) and IncA/C and H1 plasmid genes n = 493). The microarray analysis of IncA/C plasmid genes defined a core “backbone” of these plasmid genes in the isolates. The microarray also identified regions of variability associated with metal resistance that could explain the stability of MDR IncA/C plasmids in the absence of antimicrobial selective pressure. From these results, plasmid preparations from 32 isolates were selected for sequence analysis by 454 shotgun pyrosequencing. Preliminary sequencing data has confirmed the microarray data and analysis has identified and assembled contiguous sequences encoding IncA/C plasmid core genes as well as antimicrobial resistance genes. Analysis of high-throughput DNA sequencing has increased the resolution of this information and will enable an accurate determination of the history, evolution, and population dynamics of IncA/C plasmids and the MDR genes they carry in Salmonella and other bacteria.