A new dawn for chlamydia research: These important and challenging pathogens are finally yielding to modern analytic techniques

The chlamydiae are members of a diverse group of bacteria that replicate exclusively within eukaryotic cells. These pathogens cause various illnesses, including preventable blindness and urogenital infections in humans, spontaneous abortions in livestock, and fatal respiratory infections in birds. Chlamydiae shift from an infectious to a replicative form when they contact and invade host cells, and then replicate within specialized vacuoles. Until recently microbiologists studying chlamydiae relied on indirect approaches to study gene functions in these bacteria. During the past 5 years, several technical breakthroughs have led to genuine opportunities for practical genetic manipulations of these organisms. The earliest reports of what were likely chlamydial infections can be found in ancient texts, where diseases of the eye are documented. Early efforts to study the etiology of chlamydial disease trace to Czech scientists Ludwig Halberstädter and Stanislaus von Prowacek, who examined the transmissibility of the infectious agent of trachoma as early as 1907 (historical descriptions of chlamydial research can be found at www.chlamydiae.com). More information about the pathogenic nature of chlamydial organisms started to emerge in the 1920s, when doctors began associating contact with psittacine birds from Africa among Europeans and Americans who developed fatal pneumonias. Subsequent researchers carefully documented the developmental cycle of these bacteria and portrayed what they observed by microscopy in detailed pen-and-ink drawings (Fig. 1). Early chlamydial research was both challenging and fascinating, and many of the original assumptions about the organism reflected the technological limits and biases of the era. For instance, in 1934, British microbiologists Samuel Bedson and J.W. Bland described it as a virus "with affi{dotless}nities to the bacteria" when they wrote: In our opinion this virus is a micro-organism with bacterial affi{dotless}nities which is essentially an intracellular parasite and which in the early stages of multiplication produces forms much larger than normal.... in our experience, when the elementary bodies gain access to a suitable cell, either in the animal or in tissue culture, they are soon and invariably replaced by large forms. These large forms apparently multiply for a short time without much change in size, but subsequently there is a progressive decrease in size as multiplication proceeds until the stage of the elementary bodies is reached again. © 2009 American Society for Microbiology. All Rights Reserved.

Duke Scholars

Author Raphael H. Valdivia Integrative Immunobiology