Selective Pressure Potential of Antimicrobial Agents to Facilitate Spread of Resistance Plasmid (pp. 209-222)
Authors: (Keri E. Powell, Maria C. Garcia, Aaron M. Lynne, Department of Biological Sciences, Sam Houston State University, Huntsville, Texas, USA)
Abstract: Salmonellosis is of public health concern, accounting for about a quarter of all bacterial foodborne infections. According to the CDC, Salmonella enterica serovar Typhimurium is the most common Salmonella serotype reported. Of great concern is the possession and dissemination of antimicrobial resistance among Salmonella strains. Many antimicrobial resistance genes associated with Salmonella are found on conjugative plasmids. The misuse of antimicrobials in medical and animal-production settings may provide selective pressures that contribute to the proliferation of antimicrobial resistance, primarily by plasmid transfer. This study aims to present a selective pressure (i.e., varying antibiotic concentrations of four antibiotics) on the plasmid transfer rates of Salmonella via conjugation in-vitro. The four antimicrobials were selected for their plasmid-encoded resistance genes, activity against gram negative bacteria, and FDA approval for use in animal production. Successful conjugation pairs of S. Typhimurium isolates were mated under varying pressure conditions, plated on double antibiotic plates to select for transconjugants, and then conjugation rates were calculated. Preliminary results indicate a difference in conjugation rates across the four antimicrobials and within antimicrobials of varying concentration. Final results of the study may be useful in identifying antibiotics that may be more or less likely to initiate plasmid transfer between S. Typhimurium isolates in-vitro.