Comparison of the ultrastructure of small dense forms of chlamydiae and Coxiella burnetii

In the course of passaging of Coxiella burnetii (C.b.) in Alveonasus lahorensis ticks, the haemocytes contained cell forms with electrodense cytoplasm, intracytoplasmic lamellar membranes, and a peculiar limiting membrane-25 to 30 nm thick 'envelope complex'. Similar small forms occurred when C.b. had been cultured in the yolk sack of chick embryos. The dense forms of C.b. were similar to those of Rickettsiella cells. Dense forms (elementary bodies) surrounded by an 'envelope complex' were found also in some chlamydiae cultured in yolk sacs of chick embryos.