Cellular events and intracellular survival of Campylobacter jejuni during infection of HEp-2 cells

Abstract

Invasion and intracellular survival of Campylobacter jejuni in HEp-2 cells were analyzed by transmission electron microscopy and by viable counts after killing of extracellular bacteria by gentamicin. During the first 30 min after challenge, no bacteria were seen in association with the host cell. After 1 h, campylobacters apparently attached to the cell membrane, with areas of close appositions. In these areas, an intracellular network of actin-like filaments was seen beneath the plasma membrane. Other bacteria were included into endocytic vacuoles. After 3 h, an intense lysosomal response was observed in the host cells, as determined by the presence of myelinic forms and acid phosphatase activity. After 9 h, bacteria still contained in vacuoles showed signs of degradation with a change from spiral to coccal forms. Morphological evidence of phagosome-lysosome fusion was also seen, and these observations by transmission electron microscopy correlated well with a decrease in bacteria viability 9 h after challenge, as determined from separate kinetics studies. Inhibitors of phagocytosis were observed to reduce markedly the entry of C. jejuni into the cells at concentrations which apparently did not affect bacterial viability. These results suggest that the campylobacters were successively attached to the HEp-2 cell membrane, internalized by a phagocytic-like mechanism, and digested after phagosome-lysosome fusion.