Fusion of inclusions following superinfection of HeLa cells by two serovars of Chlamydia trachomatis.

We used a double-label immunofluorescence assay to examine the ability of Chlamydia trachomatis serovar F to infect and develop within HeLa 229 cells previously infected with serovar E. No exclusion to superinfection occurred for up to 24 h following infection by serovar E. The percentage of HeLa cells infected in cultures inoculated with both strains was identical to that of cells in cultures inoculated with one strain as a control. Organisms of both serovars were located within the same intracellular inclusion in 88 to 95% of HeLa cells infected with both serovars. The proportion of superinfected HeLa cells containing both strains in separate inclusions increased when there was exposure to inhibitors of cytoskeletal structure and transport. We used this inhibition to demonstrate that fusion of C. trachomatis phagosomes occurs throughout the developmental cycle.