EFFECTS OF MULTIPLICITY OF INFECTION, BACTERIAL PROTEIN-SYNTHESIS, AND GROWTH-PHASE ON ADHESION TO AND INVASION OF HUMAN CELL-LINES BY SALMONELLA-TYPHIMURIUM

Monolayers of intestine 407 (Int-407) cells were infected with the vir ulent Salmonella typhimurium strain C52, and the adhesion to and invas ion of these cells were studied. The effects of the multiplicity of in fection and growth phase of the bacteria (logarithmic versus stationar y) on the interaction with eukaryotic cells were investigated. In cont rast to other reports, we found no differences in the adhesive and inv asive capacities of bacteria derived from logarithmic- or stationary-p hase cultures. Invasion by S. typhimurium required bacterial protein s ynthesis and live Int-407 cells. Bacteria adhered equally well to dead or live Int-407 cells, which indicates that adhesion does not require metabolically active cells. Adhesion of S. typhimurium followed satur ation kinetics, with a maximum of 10 adhesive bacteria per cell. This indicates that there is a limited number of bacterial adhesion sites ( receptors) available on the surface of the host cell. Killed and live bacteria adhered equally well and competed with each other for cellula r adhesion sites. This and adhesion experiments performed in the prese nce of chloramphenicol showed that bacterial protein synthesis is not required for adhesion. The general validity of the results obtained wi th S. typhimurium C52 was confirmed by comparing the invasion and adhe sion data with those of the frequently used SL1344 and SR11 strains. I n addition, we assayed the adhesion and invasion of S. typhimurium C52 , SL1344, and SR11 and 27 S. typhimurium field isolates with Int-407, HeLa, and HEp-2 cells.