Imaging of Chlamydia and host cell metabolism.

Chlamydial infections cause a wide range of acute and chronic diseases. Chlamydia trachomatis is the most common sexually transmitted bacterium while Chlamydia pneumoniae causes infections of the upper and lower respiratory tract. Chlamydia are obligate, intracellular bacteria with a biphasic developmental cycle that involves unique metabolic changes. Aside from entering an actively replicating state, Chlamydia may also implement persistent infections depending on different microenvironmental factors. In addition, changes in local oxygen availability and the composition of surrounding host microbiota are suggested to affect chlamydial growth and metabolism. Both bacteria and host cells endure characteristic metabolic changes during infection. Technical developments in recent years enable us to separately characterize chlamydial and host cell metabolism in living cells. This article focuses on novel approaches to analyze chlamydial metabolism such as NAD(P)H fluorescence lifetime imaging by two-photon microscopy. In addition, we provide an overview regarding promising future possibilities to further elucidate host-pathogen metabolic interactions.