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Abstract
Kim Bennett

Fellow – Kim Bennett

Mentor – Noah Cohen

Project – Transfer of virulence plasmids between Rhodococcus equi strains

Objective – To evaluate the transfer of the Rhodococcus equi virulence-associated plasmid between multiple donor strains to a single recipient strain at a variety of biologically relevant temperatures.

Sample Population – 2 virulent strains (01-098 and 01-103) and 1 avirulent strain (RE123).

Procedure – The virulent and avirulent strains were grown together on a fixed filter system at 37 C, 20 C and 4 C to allow for plasmid transfer. Using antibiotic media, virulent organisms were selectively eliminated from the quantitative culture of avirulent and transconjugate organisms. Plasmid transfer was detected using a colony immunblot technique.

Results – The virulence-associated plasmid was best transferred at 37 C (estimated efficiency = 14%-24%), moderately at 20 C (estimated efficiency = 8%-19%), and rarely at 4 C (estimated efficiency = 2%-6%).

Conclusions and Clinical Relevance – The results in this study demonstrate that plasmid sharing can occur at temperatures encountered in the intestinal tract and soil where virulent and avirulent organisms may co-exist. Management strategies to reduce the virulent R. equi in the environment must contend with the transfer of the virulence-associated plasmid. Warmer temperatures appear to facilitate the efficiency of plasmid transfer.