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Abstract
Salmonella Typhimurium is an important pathogen of humans and animals. Recently, Salmonella strains have arisen that are resistant to multiple antimicrobials including third generation cephalosporins. It is unclear whether these multiple resistant isolates have a selective advantage for transmission between hosts and whether antimicrobial selective pressure adds to this advantage. This study was designed to investigate the transmissibility of a resistant strain and a sensitive strain of S. Typhimurium with and without antimicrobial selective pressure in a poultry model. The data from these studies indicated that multiple antimicrobial resistance in Salmonella isolates do lead to increased transmissibility under antimicrobial selective pressure, the sensitive Salmonella strain survived and was transmitted efficiently between animals even with antimicrobial selective pressure at MIC levels, and the sensitive Salmonella strain is capable of acquiring genes for resistance in as little as 7 days with or without exposure to antimicrobials.