**2. The Chlamydial developmental life cycle**

*Chlamydiae* are gram-negative obligate intracellular pathogens characterized by their biphasic life cycle [4–6]. *Chlamydiae* primarily infect mucosal epithelial cells and alternate between two morphologic forms. The first, known as the elementary body (EB), is the infectious form that attaches to the cell membrane of a host cell. Shortly after interacting with host cell membrane receptors, the bacterial ligands induce endocytosis of the pathogenic EB, leading to the creation of an EB-containing vacuole known as the inclusion [4]. Once inside the cell, the EB within the inclusion takes around 6–8 hours to transform into the second morphologic subtype, known as the reticulate body (RB). The RB modifies the inclusion's membrane to prevent its degradation, while also prompting migration of the inclusion toward the microtubule-organization center (MTOC) to facilitate movement toward nutrient-rich areas within the host cell (e.g., periphery of the Golgi apparatus) [4].

Due to the parasitic nature of *Chlamydiae,* these pathogens not only rely on essential nutrients from the host cell but also require several metabolic enzymes, which are subsequently hijacked from the host. Thus, approximately 8–16 hours after infection, the mid-cycle begins, where the RB produces effectors that facilitate the looting of nutrients and enzymatic hijacking [2, 4]. Finally, after 24 hours of replication and growth, RBs can revert to EBs via an asynchronous process that allows them to exit the host cell (e.g., cell lysis or extrusion). *Chlamydiae* can also transform into a third morphologic subtype under certain conditions. When *Chlamydiae* experience physiologic stressors, RBs can transform into abnormally large bacteria known as an aberrant body (AB) [4]. ABs are characterized by their non-infectious "hibernating" state, allowing them to re-enter the normal biphasic life cycle once the underlying stressor subsides to continue producing infectious EBs [4].
