could not culture C. felis using the available culturing methods of the time, so for a while thought that the causative agent might be a virus. Baker did find the causative agent when he spun the infected mouse lungs in a centrifuge. He found the elementary bodies (see Characterization sub-heading) of C. felis that had been separated from the mouse lungs, confirming that they were the causative agent of the disease. Characterization C. felis is a Gram negative (also known as diderm), microaerophilic bacterium, whose cell wall seems to lack peptidoglycan. Its morphology is that of a coccobacillus. C. felis is also an obligate intracellular pathogen that infects eukaryotic cells, specifically cats, but has zoonotic potential. The bacterium like many in its phylum, has evolved to have two distinct life stages: the elementary body (EB) and the reticulate body (RB). The EB is the infectious phase of the pathogen and is characterized by reduced metabolic activity and the inability to replicate. The exact morphology of the EB varies among species within the Chlamydiota phylum. The RB is the replicative phase of the pathogen's life cycle and has a higher metabolic activity compared to the EB. When the extracellular phase (EB) infects the host eukaryotic cell via endocytosis the bacteria transforms into the replicative phase (RB) while remaining in a membrane-bound vesicle called an inclusion. Within the inclusion the RB cells will avoid the host cell's defenses, such as lysosomes, grow, and divide by binary fission. This method of infection and replication is common among the Chlamydia genus. It is currently unknown how the bacteria receive their nutrients from the host while residing in the inclusion. Metabolism Many metabolic processes and genes are highly conserved among Chlamydia. Due to C. felis's, and Chlamydia in general, small genome, it is missing the genes for several essential enzymes for metabolic pathways, such as glycolysis and the citric acid cycle. It cannot synthesize nucleotides, nor many cofactors or amino acids. However, the bacteria's ability to synthesize and/or scavenge amino acids and nucleotides varies from species-to-species and from strain-to-strain, as shown by C. felis's ability to synthesize the tryptophan. In order to survive, C. felis will take various metabolites, such as phosphorylated sugars, and other essential molecules from the host cell. It is currently unknown exactly how the bacteria receive these molecules while residing in the inclusion. It is thought that the bacteria receive host