Chlamydia species are immortal bacteria that live and replicate inside a host cell. An elementary body is the infectious form, which has a rigid outer membrane. A reticulate body is the non-infectious form, which replicates by division, inside the cell. An elementary body invades the host cell, becomes a reticulate body, replicates by division to create new elementary bodies, and within forty-eight to seventy-two hours, new elementary bodies are released to infect new host cells. Penicillin causes the reticulate body to change shape and become larger, make more elementary bodies, and extends the life cycle of chlamydia from thirty hours to seventy-two hours.