[Inapparent persistent chlamydial infection in McCoy cells].

We have studied the phenomena of inapparent chlamydial infections in vitro using McCoy cells in culture as hosts and low doses of Chlamydia psittaci (GP-IC) as infecting agents. The results indicate that GP-IC can persist undetected at least 220 hrs in McCoy cells previously inoculated with 0.2 mL of a GP-IC preparation containing 30 ifu/mL, using the centrifuge-assisted inoculation technique. These cells were maintained in complete MEM medium supplemented with 2% v/v of foetal bovin serum (FBS). These inapparent chlamydial infections did not follow active infections (detectable chlamydial multiplication); however, they could be induced to active infections (formation of intracytoplasmic inclusions) by transfering the infected McCoy cells in complete MEM medium supplemented with 5% v/v of FBS and 1 microgram/mL of cycloheximide. Transfer of these cells in complete MEM medium supplemented with 5% v/v of FBS but without cycloheximide did not induce active infections indicating that nutritional competition was not implicated in these inapparent chlamydial infections since that medium usually support chlamydial multiplication.