4: The Eukaryotes of Microbiology
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- 4.1: Characteristics of Eukaryotic Cells
- Eukaryotic cells are defined by the presence of a nucleus containing the DNA genome and bound by a nuclear membrane (or nuclear envelope) composed of two lipid bilayers that regulate transport of materials into and out of the nucleus through nuclear pores. Eukaryotic cell morphologies vary greatly and may be maintained by various structures, including the cytoskeleton, the cell membrane, and/or the cell wall The nucleolus in the nucleus of eukaryotic cells is the site of ribosomal synthesis.
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- 4.2: Classifying Eukaryotic Microbes and Examples
- Protists are a diverse, polyphyletic group of eukaryotic organisms. Protists may be unicellular or multicellular. They vary in how they get their nutrition, morphology, method of locomotion, and mode of reproduction. Important structures of protists include contractile vacuoles, cilia, flagella, pellicles, and pseudopodia; some lack organelles such as mitochondria. Taxonomy of protists is changing rapidly as relationships are reassessed using newer techniques.
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- 4.3: Mycoses of the Skin and Eyes
- Mycoses can be cutaneous, subcutaneous, or systemic. Common cutaneous mycoses include tineas caused by dermatophytes of the genera Trichophyton, Epidermophyton, and Microsporum. Tinea corporis is called ringworm. Tineas on other parts of the body have names associated with the affected body part. Aspergillosis is a fungal disease caused by molds of the genus Aspergillus. Primary cutaneous aspergillosis enters through a break in the skin, such as the site of an injury or a surgical wound.
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- 4.4: Protozoan and Helminthic Infections of the Eyes
- The protozoan Acanthamoeba and the helminth Loa loa are two parasites that can breach the skin barrier, causing infections of the skin and eyes. Acanthamoeba keratitis is a parasitic infection of the eye that often results from improper disinfection of contact lenses or swimming while wearing contact lenses. Loiasis, or eye worm, is a disease endemic to Africa that is caused by parasitic worms that infect the subcutaneous tissue of the skin and eyes. It is transmitted by deerfly vectors.
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- 4.5: Respiratory Mycoses
- Fungal pathogens are ubiquitous in the environment. Serological studies have demonstrated that most people have been exposed to fungal respiratory pathogens during their lives. Yet symptomatic infections by these microbes are rare in healthy individuals. This demonstrates the efficacy of the defenses of our respiratory system. In this section, we will examine some of the fungi that can cause respiratory infections.
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- 4.6: Fungal Infections of the Reproductive System
- Candida spp. are typically present in the normal microbiota in the body, including the skin, respiratory tract, gastrointestinal tract, and female urogenital system. Disruptions in the normal vaginal microbiota can lead to an overgrowth of Candida, causing vaginal candidiasis. Vaginal candidiasis can be treated with topical or oral fungicides. Prevention is difficult.
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- 4.7: Protozoan Infections of the Reproductive System
- Trichomoniasis is a common STI caused by Trichomonas vaginalis. T. vaginalis is common at low levels in the normal microbiota. Trichomoniasis is often asymptomatic. When symptoms develop, trichomoniasis causes urinary discomfort, irritation, itching, burning, discharge from the penis (in men), and vaginal discharge (in women). Trichomoniasis is treated with the antiflagellate drugs tinidazole and metronidazole.
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- 4.8: Protozoan Infections of the Gastrointestinal Tract
- Like other microbes, protozoa are abundant in natural microbiota but can also be associated with significant illness. Gastrointestinal diseases caused by protozoa are generally associated with exposure to contaminated food and water, meaning that those without access to good sanitation are at greatest risk. Even in developed countries, infections can occur and these microbes have sometimes caused significant outbreaks from contamination of public water supplies.
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- 4.9: Parasitic Infections of the Circulatory and Lymphatic Systems
- Some protozoa and parasitic flukes are also capable of causing infections of the human circulatory system. Although these infections are rare in the US, they continue to cause widespread suffering in the developing world today. Malaria, toxoplasmosis, babesiosis, Chagas disease, leishmaniasis, and schistosomiasis are discussed in this section.
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- 4.10: Helminthic Infections of the Gastrointestinal Tract
- Helminths are widespread intestinal parasites. These parasites can be divided into three common groups: round-bodied worms also described as nematodes, flat-bodied worms that are segmented (also described as cestodes), and flat-bodied worms that are non-segmented (also described as trematodes). The nematodes include roundworms, pinworms, hookworms, and whipworms. Many of these parasites are so well adapted to the human host that there is little obvious disease.
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- 4.11: Neuromycoses and Parasitic Diseases of the Nervous System
- Fungal infections of the nervous system, called neuromycoses, are rare in healthy individuals. However, neuromycoses can be devastating in immunocompromised or elderly patients. Several eukaryotic parasites are also capable of infecting the nervous system of human hosts. Although relatively uncommon, these infections can also be life-threatening in immunocompromised individuals. In this section, we will first discuss neuromycoses, followed by parasitic infections of the nervous system.
Thumbnail: Mold growing on a clementine . (CC SA-BY 3.0; ).