TETRACYCLINE FLUORESCENCE IN PERMEABILITY STUDIES OF MEMBRANES AROUND INTRACELLULAR PARASITES.

Certain protozoa, bacteria, and viruses when phagocytosed by host cells become surrounded by an intracytoplasmic boundary. This membrane prevents the fluorescent antibiotic tetracycline from entering the parasites when it is added to the medium, since they show no fluorescence, whereas extracellular parasites are immediately visible. As soon as the host cell dies, the intracellular parasites also become visible. This indicates that the boundary probably is of host origin. This phenomenon provides a means for selective permeability studies of such boundaries. A similar exclusion of tetracycline from certain extracellular parasites is seen in the presence of whole serum.