Table 1

 Direct microscopic assessment of the cytopathic effect of chlamydia EBs on McCoy cell monolayers

Time after inoculation (hours)Level of visual cytotoxicity seen in McCoy cell monolayers after infection with chlamydia EBs at the indicated MOI*
Chlamydia muridarumSerovar DSerovar HSerovar L2
*Confluent McCoy cell monolayers were infected at MOIs of 1.5–100 and incubated at 37°C in the presence of 10 µg/ml of rifampicin and 5 µg/ml of doxycycline. The cytopathic effect was evaluated immediately after infection and at 1, 2, 4, and 6 hours post-infection, and was subjectively scored from negative (–) to positive using a scale of 1 to 4, on the basis of the degree of loss in cell membrane integrity and apparent lysis compared with non-infected control monolayers: 4, complete disruption with apparent lysis; 3, significant perturbation, with some level of apparent lysis; 2, significant membrane perturbation; 1, slight but noticeable affect; –, same as control. Immediately after centrifugation, all monolayers inoculated at MOIs of 25 and 100 contained cells with multiple intracellular vacuoles that were not seen at lower MOIs or in uninoculated monolayers. No difference in degree of vaculation was seen among the strains and no cytopathic score was assigned to this observation because over the course of the experiment these vacuoles disappeared in surviving cells, being completely absent in L2 inoculated cells by 4 hours.
EB, elementary body; MOI, multiplicity of infection.