![]() ![]() ![]() The reticulate bodies multiply and release more elementary bodies when the cell dies after the Chlamydia uses all of the host cell’s ATP. Once inside the host cell, the elementary bodies turn into active reticulate bodies. Chlamydia begins infection of a host when the metabolically inactive elementary bodies enter an epithelial cell. Figure 2 illustrates the life cycle of Chlamydia.įigure 2. The metabolically and reproductively inactive elementary bodies are the endospore-like form of intracellular bacteria that enter an epithelial cell, where they become active. ![]() Members of this genus are extremely resistant to the cellular defenses, giving them the ability to spread from host to host rapidly via elementary bodies. typhi, causes a less severe disease known as murine or endemic typhus, which is still observed in the southwestern United States during warm seasons.Ĭhlamydia is another taxon of the Alphaproteobacteria. prowazekii infects human endothelium cells, causing inflammation of the inner lining of blood vessels, high fever, abdominal pain, and sometimes delirium. It causes epidemic typhus, a severe infectious disease common during warfare and mass migrations of people. (credit: modification of work by Centers for Disease Control and Prevention)Īnother species of Rickettsia, R. rickettsii, which causes Rocky Mountain spotted fever, is shown infecting the cells of a tick. Rickettsias require special staining methods to see them under a microscope. rickettsii infects ticks and can be transmitted to humans via a bite from an infected tick (Figure 1).įigure 1. rickettsii causes Rocky Mountain spotted fever, a life-threatening form of meningoencephalitis (inflammation of the membranes that wrap the brain). include a number of serious human pathogens. They cannot synthesize their own adenosine triphosphate (ATP), and, therefore, rely on cells for their energy needs. When not growing inside a host cell, Chlamydia and Rickettsia are metabolically inactive outside of the host cell. The unifying characteristic of this class is that they are oligotrophs, organisms capable of living in low-nutrient environments such as deep oceanic sediments, glacial ice, or deep undersurface soil.Īmong the Alphaproteobacteria are two taxa, chlamydias and rickettsias, that are obligate intracellular pathogens, meaning that part of their life cycle must occur inside other cells called host cells. The first class of Proteobacteria is the Alphaproteobacteria. The Proteobacteria are further divided into five classes: Alphaproteobacteria, Betaproteobacteria, Gammaproteobacteria, Deltaproteobacteria, and Epsilonproteobacteria (see Taxonomy of Clinically Relevant Microorganisms). It includes many bacteria that are part of the normal human microbiota as well as many pathogens. This phylum of gram-negative bacteria subsequently received the name Proteobacteria. In 1987, the American microbiologist Carl Woese (1928–2012) suggested that a large and diverse group of bacteria that he called “purple bacteria and their relatives” should be defined as a separate phylum within the domain Bacteria based on the similarity of the nucleotide sequences in their genome. Give an example of a bacterium in each class of Proteobacteria.Describe the unique features of each class within the phylum Proteobacteria: Alphaproteobacteria, Betaproteobacteria, Gammaproteobacteria, Deltaproteobacteria, and Epsilonproteobacteria. ![]()
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