Identification of diminished tissue culture invasiveness among multiple antibiotic resistant Salmonella typhimurium DT104

Salmonella infections continue to cause gastrointestinal and systemic disea se throughout the world. Salmonella typhimurium further poses a major healt h concern due to its apparent enhanced ability to acquire multiple antibiot ic resistance genes. Currently it is unclear if multiresistant S. typhimuri um are more or less pathogenic than non-resistant counterparts. Using an in vitro invasion assay, we evaluated the relative pathogenicity of over 400 multiresistant S. typhimurium isolates. Our studies failed to identify any "hyperinvasive" isolates. However, we identified 12 isolates exhibiting inv asive phenotypes that were constrained relative to controls. These "hypoinv asive" strains were found in a variety of phagetypes all possessing at leas t a hexaresistant profile. Further studies revealed that the alterations in invasion were not due to changes in adherence. Limited studies exploring i n vivo virulence revealed a mildly decreased ability to cause murine lethal ity for the hypoinvasive strain examined. These results indicate that the a bility to cause disease is not increased but is rather mildly attenuated fo r certain isolates of multiresistant S. typhimurium. (C) 2000 Academic Pres s.