SUMMARY. When fimbriate (Fim +) strains of Salmonella typhimurium were grown in static broth, many bacteria were in the fimbriate phase and bore fimbrial mannose-sensitive haemagglutinin (MSHA) that enabled them to adhere to guinea-pig and other erythrocytes and to agglutinate them in rocked tile and static settling tests. When either Fim+ or Fim-strains were grown on phosphate-buffered nutrient agar, the bacteria formed a diffusible, mannose-resistant haemagglutinin (MRHA) that gave dispersed sediments with sheep and pig erythrocytes in static settling tests, but without evidence of bacterial adhesion to the erythrocytes. On exposure, from above or from below, to cultured HEp2 and HeLa cells for 30 or 90 min at 37"C, motile MSHA-rich, MRHA-negative broth-grown bacteria adhered to the cells in large numbers (e.g., 20-100/cell), but motile MSHA-negative, MRHA-negative broth-grown bacteria and non-motile MSHA-negative, MRHA-rich agar-grown bacteria adhered in only small numbers (usually < l/cell). Thus, strong adhesiveness of bacteria for cultured cells in vitro appears to depend upon the presence of MSHA, not MRHA, and as Fim-(MSHA-negative) strains of S. typhimurium are known to be highly infective in animals, a strong-reaction in the in-vitro model does not reflect a property of the bacteria essential for infectivity in vivo. INTRODUCTIONThe critical initial step in infection with salmonellae and shigellae is their association with the surface of, and penetration into, intestinal epithelial cells (Labrec et al., 1964;Takeuchi, 1967). Penetration is by endocytosis, an energy-requiring act of engulfment by the cells, induced by contact with the bacteria, but is also partly dependent on active bacterial metabolism (Kihlstrom and Edebo, 1976; Kihlstrom and Nilsson, 1977;Hale and Bonventre, 1979). It is generally assumed that a firm adhesion of the bacterium to the cell membrane is a prerequisite, if not the stimulant, of endocytosis (Jones, Richardson and Vanden Bosch, 1980), but the mechanism of this adhesion is still unclear. The strongest adhesive property in salmonellae and shigellae is that due to type-1 fimbriae that bind to mannose-like receptors at cell surfaces. Within a few minutes at room temperature, type-1 fimbriate bacteria adhere firmly to epithelial cells in a wet film and agglutinate erythrocytes on a rocked tile, activities that are inhibited by the presence of D-mannose or a-methylmannoside (Duguid and Gillies, 1957;Duguid, Anderson and Campbell, 1966;Duguid and Old, 1980). Thus, the fimbrial adhesive factor is referred to as a mannose-sensitive (MS) adhesin or haemagglutinin (HA).But this fimbrial MSHA is not essential for infection because many strains in different serotypes of Salmonella and Shigella are non-fimbriate, e.g., 14% of Salmonella typhimurium strains (Duguid et al., 1975), and do not adhere to intestinal epithelial cells in short-term tests at room temperature (Duguid and Gillies, 1957;Duguid et al., 1966). Moreover, in mice challenged by mouth with equal inocula of fimbriate and ...
SUMMARY. Type-3 fimbriae isolated from members of five different species of Klebsiella were 4-5 nm in diameter and agglutinated the tannic acid-treated erythrocytes of ox and, in some cases, the untanned erythrocytes of fowl. In sodium dodecyl sulphate-polyacrylamide gel electrophoresis, the type-3 fimbrial proteins had mol. wts in the range 19 500-21 500. Hydrophobic amino acids comprised 39.6% of all the amino acids of the type-3 fimbrial protein of K. oxytoca strain 70/ 1. The type-1 fimbrial protein of Klebsiella had a mol. wt of c. 18 000 and the type-1 fimbriae were serologically distinct from the type-3 fimbriae. Our results for the type-3 fimbriae of Klebsiella were compared with those of others for morphologically similar and serologically related thin fimbriae of Salmonella and Yersinia.
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