Attachment and infectivity of C. trachomatis (serovar L2) for CHO-K1, heparan sulfate-deficient CHO-224, and glucuronosyltransferase I-complemented CHO-224.GOO. At approximately 24 h postinfection, chlamydial inclusions were detected by immunofluorescence and enumerated by counting inclusions (IFU). Similar data were obtained in at least three independent experiments. Real-time quantitative PCR was used to determine the numbers of EB genome equivalents (GE) in wells containing cell monolayers after 2 h postinfection (HPI) at room temperature and washing, representing the number of chlamydiae attached to the monolayer (Attachment), and at 24 HPI, representing the amount of chlamydial growth (Infectivity).