Evaluation of invasion-conferring genotypes and antibiotic-induced hyperinvasive phenotypes in multiple antibiotic resistant Salmonella typhimurium DT104

Antibiotic resistance in pathogenic bacteria is a problem in both industria lized and developing countries. This is especially evident in Salmonella ty phimurium, a foodborne pathogen that causes gastrointestinal and systemic d isease throughout the would. S. typhimurium DT104 further poses a major hea lth concern due to its apparent enhanced ability to acquire multiple antibi otic resistance genes and its putative hypervirulent phenotype. Recently, w e demonstrated that multiresistant S. typhimurium do not appear to be more invasive than non-resistant cohorts. In the present study, we evaluated the presence of Salmonella pathogenicity island 1 (SPI1) flanking and internal sequences in over 400 isolates of multiresistant S. typhimurium. With thes e same isolates, we also used a tissue culture invasion assay to evaluate a potential relationship between antibiotic exposure and a hyperinvasive phe notype. Our studies revealed that SPI1 flanking sequences are similar in mu ltiresistant and non-resistant S. typhimurium. Furthermore, we failed to id entify any isolates that were hyperinvasive in the presence of any of the 1 4 antibiotics evaluated. These results further indicate that the putative h ypervirulence of multiresistant S. typhimurium is not likely to occur at th e level of invasion.