Title: Inc A/C Plasmids in Multidrug resistant Salmonella enterica Authors
Submitted to: American Society for Microbiology
Publication Type: Abstract Only
Publication Acceptance Date: February 20, 2009
Publication Date: May 17, 2009
Citation: Lindsey, R.L., Cray, P.J., Frye, J.G., Meinersmann, R.J. 2009. Inc A/C Plasmids in Multidrug resistant Salmonella enterica [abstract]. American Society for Microbiology. May 17-21,2009. Philadelphia, PA. A-092. Technical Abstract: Bacteria plasmids are fragments of extra-chromosomal double stranded deoxyribonucleic acid (DNA) that can contain a variety of genes beneficial to the survival of the host bacteria. Classification and tracking of plasmids is beneficial because they are potentially a medium of horizontal gene transfer for drug resistance. Plasmids can be classified according to incompatibility (Inc) types which are based on the inability of plasmids with the same replication mechanism to exist in the same cell. In Enterobacteriaceae there are 26 known Inc types or replicon types. Certain replicon types such as Inc A/C are associated with multidrug resistance (MDR). The objective of this study was to characterize a collection of 437 Salmonella enterica isolates from different animal sources for their antimicrobial resistance phenotype, plasmid replicon type and, in some cases, pulsed field gel electrophoresis (PFGE) pattern to learn more about the distribution of MDR in relation to replicon types. A previously developed set of three multiplex PCR-based replicon typing assays was used to distinguish 18 replicon types. Linkage analysis was completed with antimicrobial resistance phenotype, serovars, replicon types, and an Inc A/C subset. Cluster analysis based on PFGE of a subset of 216 isolates from 35 different serotypes show 155 unique types suggesting a variable population. Cluster analysis shows Inc A/C positive strains form groups based on serovar and MDR whereas Inc I1 positive isolates did not appear to be clonally distributed. This probably indicates that Inc A/C plasmids have been stably associated with clones for a very long time while Inc I1 plasmids are much more mobile. Inc A/C plasmids were prevalent in MDR isolates with the notable exception of Salmonella enterica serovar Typhimurium. Our results suggest that some strains, notably serovar Typhimurium and closely related types, may have once carried the plasmid but the resistance genes were transferred to the chromosome with subsequent loss of the plasmid.