Infectivity of Chlamydia psittaci of bovine and ovine origins for cultured cells

The infectivity of 2 strains of Chlamydia psittaci of mammalian origin were studied in mouse L cells. Infectivity was enhanced by centrifuging the chlamydial inoculum onto the cell monolayer. Infectivity increased as force of centrifugation increased. The enhanced infectivity was not caused by centrifugal sedimentation of chlamydiae, since centrifugation longer than 10 minutes and an inoculum dose larger than 0.4 ml did not further enhance infectivity. Centrifuge-enhanced adsorption was temperature dependent, because infection was not detected when stationary or centrifuge-assisted adsorption occurred at less than 15 C. Infectivity was higher in cultures centrifuged at 37 degrees C than in cultures centrifuged at room temperature. Treatments of cells with cycloheximide, colchicine, and hydrocortisone enhanced infectivity of chlamydiae above that of untreated cells. In addition, developing chlamydial inclusions were larger and easier to observe in colchicine-treated cells. Infectivity was thought to be enhanced in colchicine-treated cells, because cells with depolymerized microtubules provided favorable conditions for the early phases of chlamydial multiplication. Treatment of cells with cytochalasin B, carbachol, cGMP, lumicolchicine, or vinblastine did not significantly alter chlamydial infectivity.