Early morphological changes of intracellular bacteria in Salmonella typhimurium infection of the guinea pig conjunctival epithelium.

Conjunctival epithelium of the guinea pig was incubated with a virulent strain of Salmonella typhimurium 395 MS for 1 h. Intracellular bacteria were observed in superficial and intermediate cell layers, but not in basal cells. The majority of the bacteria were located within primary or secondary phagosomes; a few were seen free in the cytoplasm. A number of intraphagosomal bacteria showed morphological signs of degradation. Ultrastructurally, the initial phases of Salmonella typhimurium infection of the guinea pig conjunctival epithelium appear to be consistent with endocytic uptake of bacteria by the epithelial cells, followed by their degradation in secondary phagosomes. The conjunctival epithelial cells seem able to inactivate a certain number of virulent bacteria and thus, to a degree, to control the infection in its early phase with defence mechanisms pertaining to the cells themselves, without support from the professional phagocytic cells.