Abstract
Guinea pig cell monolayer-grown chlamydiae (CGO) differed from [chicken] egg-grown organisms (EGO) in their increased spontaneous infectivity relative to centrifuge assisted infectivity for monolayers. For each population spontaneous:centrifuge-assisted infectivity ratios were constant over a wide dose range. Spontaneous infection increased linearly with time and could not be exhausted from either population by prolonged adsorption; there was no change in infectivity ratios in residual supernatants. One passage of EGO through monolayers gave CGO with stable infectivity properties not increased by further cell passage yet reverting on a single passage in eggs. Spontaneous infection of monolayers with EGO gave progeny with the same infectivity ratios as monolayers infected with EGO by cnetrifugation. The change in properties following EGO infection of monolayers occurred prior to natural release from cells. EGO and CGO are 2 phenotypically distinct, homogeneous populations. The 2 infection modes are not properties of subpopulations within EGO and CGO. The relationship of these observations on chlamydiae to other possible host-imposed phenomena is considered.