Obligate Intracellular Parasites

Obligate intracellular parasites are unable to reproduce outside a host cell. In general, the term only refers to those that infect eukaryotic cells. By living within eukaryotic cells, these bacteria are supplied with a readily available source of compounds they would otherwise need to synthesize for themselves. As a result, most species of these genera have lost the ability to synthesize substances needed for extracellular growth. Bacterial examples include members of the genera Rickettsia, Orientia, Ehrlichia, Coxiella, and Chlamydia, which are all tiny Gramnegative rods or coccobacilli.

The Genera Rickettsia, Orientia, and Ehrlichia

Species of Rickettsia, Orientia, and Ehrlichia are responsible for several serious human diseases that are spread when a bloodsucking arthropod such as a tick or louse that has fed on an infected animal transfers bacteria to a human from whom it takes another blood meal. Rickettsia rickettsii causes Rocky Mountain spotted fever, R. prowazekii causes epidemic typhus, O. tsutsugamushi causes scrub typhus, and E. chaffeenis causes human ehrlichiosis.

The Genus Coxiella

The only species of Coxiella, C. burnetii, is an obligate intracel-lular bacterium that survives well outside the host cell and is transmissible from animal to animal without necessarily involving a blood-sucking parasite. During its intracellular growth, C. burnetii forms sporelike structures that later allow it to survive in the environment, although the structures lack the extreme resistance to heat and disinfectants characteristic of most endospores (figure 11.29). Coxiella burnetii causes Q fever of humans, a disease most often acquired by inhaling bacteria shed from infected animals.

The Genus Chlamydia

Chlamydia species are quite different from the other obligate intracellular parasites. They are transmitted directly from person to person rather than through the bite of a blood-sucking arthropod, and they have a unique growth cycle (figure 11.30). Inside the host cell, they initially exist as a fragile non-infectious form called a reticulate body that reproduces by binary fission. Later in the infection, the bacteria differentiate into a smaller, dense-appearing infectious form called an ele-

Coxiella Burnetii Cell Structure

Figure 11.29 Coxiella Color-enhanced transmission electromicrographs of C. burnetii. The oval copper-colored object is the sporelike structure.

Figure 11.29 Coxiella Color-enhanced transmission electromicrographs of C. burnetii. The oval copper-colored object is the sporelike structure.

Tissue Culture Chlamydia

Figure 11.30 Chlamydia Growing in Tissue Cell Culture The numbers indicate the development from the dividing reticulate body to an infectious elementary body.

Figure 11.30 Chlamydia Growing in Tissue Cell Culture The numbers indicate the development from the dividing reticulate body to an infectious elementary body.

mentary body that is released upon death and rupture of the host cell. The cell wall of Chlamydia species is highly unusual among the Bacteria in that it lacks peptidoglycan, although it has the general appearance of a Gram-negative type of cell wall. Chlamydia trachomatis causes eye infections and a sexually transmitted disease that mimics gonorrhea, C. pneumoniae causes atypical pneumonia, and C. psittaci causes psittacosis, a form of pneumonia. ■ Chlamydia trachomatis, p. 646

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Detox Diet Basics

Detox Diet Basics

Our internal organs, the colon, liver and intestines, help our bodies eliminate toxic and harmful  matter from our bloodstreams and tissues. Often, our systems become overloaded with waste. The very air we breathe, and all of its pollutants, build up in our bodies. Today’s over processed foods and environmental pollutants can easily overwhelm our delicate systems and cause toxic matter to build up in our bodies.

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  • gebre
    What is obligate intracellular parasite?
    3 years ago
  • phillipp
    What is obligate intracelular parasites?
    3 years ago
  • NIKLAS
    What is elementary body of parasite?
    2 years ago
  • Fiorenzo
    What is obligate host?
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  • Eugenia
    How to culture obligate intracellular parasites?
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  • andrea
    What are the obligate intracellular bacteria?
    2 years ago
  • dennis
    Is malara a obligate intracellular organism?
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