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Title: Analysis of antimicrobial resistance mechanisms in MDR bacteria by microarray and high-throughput sequencing

item Frye, Jonathan

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 10/26/2012
Publication Date: 11/1/2012
Citation: Frye, J.G. 2012. Analysis of antimicrobial resistance mechanisms in MDR bacteria by microarray and high-throughput sequencing. International Conference of the Korean Society of Veterinary Science. November 1-2, 2012. Seoul, Republic of Korea.

Interpretive Summary:

Technical Abstract: Antimicrobial resistance in pathogenic bacteria is a major concern in human and animal health. The National Antimicrobial Resistance Monitoring System (NARMS) was designed by the CDC, FDA, and USDA to monitor antimicrobial resistance in the U.S. The Bacterial Epidemiology and Antimicrobial Resistance research unit analyzes antimicrobial resistance in bacteria isolated from animals by NARMS. Multi drug resistance (MDR) in the foodborne pathogen, Salmonella enterica, has increased during the first 11 years of the NARMS program. To investigate this, microarray methods were developed to identify the mechanisms of resistance in Salmonella. In a study of diagnostic isolates collected from clinically ill animals in 2005, MDR in Salmonella was associated with the presence of IncA/C plasmids. Genomic analysis with microarrays determined that there were two major lineages. On-going studies involve sequencing these plasmids to determine how they evolved and possibly spread in Salmonella and other bacteria. Another study was initiated to investigate MDR in Salmonella isolated from healthy food animals that could potentially lead to MDR foodborne human infections. This focused on Salmonella serovar Typhimurium as it is the most prevalent penta-resistant (Ampicillin, Chloramphenicol, Streptomycin, Sulfametoxizolw, and Tetracycline, aka ACSSuT) serovar isolated from animals. To explore this, one isolate each from cattle, poultry, and swine with at least the ACSSuT phenotype were selected for each year of NARMS from 1997-2007 (n=33). These isolates were also analyzed by microarray, which detected resistance and plasmid genes in all isolates. Cluster analysis based on this data separated the isolates into two major groups. The resistance genes detected in group 1 were similar to those usually present in the class I integron found in Salmonella Genomic Island I (SGI1) of Salmonella Typhimurium DT104. Isolates in group 2 exhibited genes that were usually associated with IncA/C plasmids encoding the MDR-AmpC phenotype. Linkage Disequilibrium detected significant associations between plasmid Inc type, phage type, and animal source. These data suggest that MDR in Salmonella Typhimurium is associated with DT104/SGI1 or IncA/C MDR-AmpC encoding plasmids. Additionally, these genetic elements are largely similar throughout the first 11 years of NARMS animal surveillance suggesting a high degree of stability among AR genes associated with this serotype.