Submitted to: Infection and Immunity
Publication Type: Peer reviewed journal
Publication Acceptance Date: 7/15/2003
Publication Date: 11/1/2003
Citation: ALTHOUSE, C., PATTERSON, S., CRAY, P.J., ISAACSON, R.E. 2003. TYPE 1 FIMBRIAE OF SALMONELLA ENTERICA SEROVAR TYPHIMURIUM BIND TO ENTEROCYTES AND CONTRIBUTE TO COLONIZATION OF SWINE IN VIVO. INFECTION AND IMMUNITY. 71(11):6446-6452. Interpretive Summary: Salmonella are bacteria that often cause food borne illness, particularly in the young, the elderly and those with diseases such as cancer and AIDS that compromise the immune system. However, Salmonella are ubiquitous in nature and most warm blooded animals can harbor Salmonella without causing illness, including food animals such as cattle, swine and poultry. Salmonella strain 798 was obtained from a pig which was ill and could also be harbored by the pig long after the illness had resolved. This strain also is known to exist in two forms, one form adheres to intestinal cells and one form is non-adherent. Interestingly, it appear that strain 798 can readily switch between the two forms. We conducted studies to characterize additional differences between the two forms of strain 798. Bacteria which are adherent are more readily taken up by white blood cells compared to non-adherent bacteria. However, once in the white blood cell, non-adherent cells die while adherent cells survive. We observed that tiny appendages, called fimbriae, located on the outside of adherent cells were missing on non-adherent cells. Infection of mice and pigs indicated that non-adherent bacteria could not attach to the intestine of mice or pigs but could spread throughout the body in mice. These results demonstrated that fimbriae are important for attachment in the intestine and while they are not important for ingestion by white blood cells, they may be important for survival in the host. These data are important for scientists and companies who may be devising ways to interrupt adherence thus limiting the probability that disease will occur.
Technical Abstract: Salmonella typhimurium strain 798 is a clinical isolate from a pig and is known to be able to cause persistent, asymptomatic infections. This strain also is known to exist in two phenotypes (adhesive and non-adhesive to enterocytes) and can switch between the two phenotypes at a rate consistent with phase variation. Cells in the adhesive phenotype are more readily phagocytized by leukocytes compared to non-adhesive cells. Once in a leukocyte adhesive phase cells survive while non-adhesive phase cells die. In the present study non-adhesive mutants were obtained using the transposon TnphoA. A non-adhesive mutant was selected for study and by electron microscopy shown not to produce fimbriae. The gene encoding the adhesin was cloned and sequenced. Based on its sequence, the adhesin was shown to be FimA, the major subunit of type 1 fimbriae. The non-adhesive mutant was attenuated in its ability to colonize both mouse and pig intestines, but remained capable of systemic spread in mice. The non-adhesive mutant was phagocytized to the same extent as parental cells in the adhesive phase and then survived intracellularly. These results demonstrated that type 1 fimbriae were important for attachment to enterocytes and promoted intestinal colonization. However, they were not important in promoting phagocytosis or intracellular survival.