Microbiology Chapter 11: Eukaryotic Microbes and Invertebrate Infectious Agents PDF

CHAPTER 11 Eukaryotic Microbes and Invertebrate Infectious Agents Copyright © 2021 W. W. Norton & Company, Inc. Eukaryotic Microbes and Invertebrate Infectious Agents Chapter Objectives ▪ Define the major categories of eukaryotic microbes and invertebrate parasites. ▪ Describe the role of f...

CHAPTER 11 Eukaryotic Microbes and Invertebrate Infectious Agents Copyright © 2021 W. W. Norton & Company, Inc. Eukaryotic Microbes and Invertebrate Infectious Agents Chapter Objectives ▪ Define the major categories of eukaryotic microbes and invertebrate parasites. ▪ Describe the role of fungi in human disease. ▪ Describe the role of protists in human disease. ▪ Outline the infectious cycles of eukaryotic parasites. 2 11.1 Eukaryotes: An Overview – 1 Section Objectives ▪ Explain the processes of asexual (vegetative) reproduction and sexual reproduction. ▪ Distinguish the key traits of fungi, algae, amebas, ciliates, and trypanosomes. ▪ Distinguish between microbial and invertebrate parasites. 3 11.1 Eukaryotes: An Overview – 2 ▪ What is the structure of eukaryotic cells? Nucleus – Linear chromosomes Membranous organelles – ER – Golgi – Vacuoles (granules) Mitochondria Chloroplasts 4 Reproduction of Eukaryotic Cells – 1 ▪ Mitosis is the process of segregating the two copies of all chromosomes evenly into the daughter cells. ▪ Many eukaryotic microbes, such as yeasts, can proliferate indefinitely by mitosis, a process called asexual reproduction or vegetative reproduction. 5 Reproduction of Eukaryotic Cells – 2 ▪ The process of gamete formation requires a special modification of mitotic cell division called meiosis. Zygote (diploid form) 6 ▪ In the haploid form, the protozoa requires fewer resources, resulting in less genetic variation and fewer antigenic changes. ▪ As the protozoa transitions to the diploid form, increased genetic diversity occurs, allowing it to better adapt to new hosts or changing environments. ▪ This genetic variation in the diploid stage enhances the parasite's ability to evade the host's immune system and thrive in different conditions. ▪ Eukaryotes → animal and plant. ▪ Microbial eukaryotes are classified traditionally as fungi, protozoa, and algae. ▪ Fungi: Hyphae and yeast. ▪ Protozoa: amebas and paramecia (microscopic motile life forms that appear more like microscopic animals. Protozoa meaning “first animals.” ▪ Protist: Algae + Protozoa (not animals, plants or fungi) The microscopic forms of fungi, protozoa, and algae are all considered “microbial eukaryotes.” 9 Diversity of Eukaryotic Microbes – 2 Not considered microbes 10 1. Helminths (Parasitic Worms) Many human pathogens. Includes organisms like roundworms (nematodes), tapeworms (cestodes), and flukes (trematodes). They are highly prevalent worldwide and cause diseases such as schistosomiasis, ascariasis, and filariasis. From: https://medizzy.com/feed/33652279 D Despommier, RW Gwadz, PJ Hotez, CA Knirsch Parasitic diseases (5th edn.), Apple Tree Production, New York (2005) 2. Fungi Many human pathogens. Includes yeasts, molds, and dimorphic fungi. Pathogenic fungi include Candida, Aspergillus, and Cryptococcus (athlete’s foot to life-threatening systemic infections). From: https://commons.wikimedia.org/wiki/File:Teigne_tondante_enfant.jpg From: https://dermnetnz.org/topics/tinea-pedis 3. Apicomplexans Many human pathogens. These protozoans include Plasmodium (causes malaria), Toxoplasma gondii, and Cryptosporidium. They are responsible for serious diseases like malaria, toxoplasmosis, and cryptosporidiosis. From: https://www.aapos.org/glossary/toxoplasmosis ▪ 4. Trypanosomes Several human pathogens. Includes species like Trypanosoma brucei (causes African sleeping sickness) and Trypanosoma cruzi (Chagas disease). These protozoa are transmitted by insects and cause severe systemic diseases. ▪ 5. Amebas Several human pathogens. Includes Entamoeba histolytica (amoebiasis), and free-living amoebae like Naegleria fowleri (primary amoebic meningoencephalitis). Most amebas are not pathogenic to humans. From: https://radiopaedia.org/articles/amoebic-hepatic-abscess ▪ 6. Metamonads Some human pathogens. Includes Giardia lamblia (giardiasis) and Trichomonas vaginalis (trichomoniasis). From: https://www.amboss.com/us/knowledge/vulvovaginitis ▪ 7. Arthropods Few direct human pathogens, but many are vectors. Some arthropods (e.g., scabies mites, lice) directly infect humans. Most arthropods (like mosquitoes, ticks, and fleas) are vectors for other pathogens. ▪ 8. Ciliates Few human pathogens. The primary human pathogen is Balantidium coli (balantidiasis). ▪ 9. Microsporidia Few human pathogens. These are obligate intracellular parasites that can cause disease, especially in immunocompromised individuals (e.g., Enterocytozoon bieneusi), but they are relatively rare compared to other eukaryotic pathogens. ▪ 10. Algae Few human pathogens. Algae are mostly non-pathogenic to humans. However, some species, like Prototheca (a rare algal pathogen), can cause protothecosis in immunocompromised individuals. Toxic algal blooms (typically cause poisoning rather than infection). 11.2 Fungi and Microsporidians Section Objectives ▪ Describe the diseases caused by yeast. ▪ Describe the structure of the fungal mycelium. ▪ Describe how different types of fungi and microsporidians cause disease. 19 Yeasts Are Single-Celled Fungi ▪ Single-celled fungi are known as yeasts. ▪ They are capable of sexual and asexual reproduction. ▪ Yeasts have the advantage of rapid growth and dispersal in aqueous environments. Candida albicans Pneumocystis jirovecii (yeast-form ascomycete). Cryptococcus neoformans (yeast-form basidiomycete). 20 ▪ Some yeasts are asexual, whereas others alternate between diploid (2n) and haploid (n) forms, a life cycle known as alternation of generations (“dimorphic” fungi) → C. albicans an example. ▪ Hyphae have tough cell walls → chitin (acetylated amino- polysaccharide) stronger than steel (multiple hydrogen bonds between fibers) → is often combined with other polymers such as glucans, mannans, and proteins (vary in composition and structure among different types of fungi). ▪ Septate or non-septate: ▪ Mycelium: ▪ Specialized hyphae: Mitotic division → Filamentous fungi → run out of nutrients? → Meiosis to form gametes → turn into spores From: https://www.ahmadcoaching.com/2023/03/structure-of-the-fungi-hyphae-mycelium-spores-septa-rhizoids.html  Cholesterol? Triazoles? Garcia-Rubio, R. et al., 2020 Case History: Fungus Growing in the Lung – 1 ▪ Frank, a 45-year-old man, visited the hospital with respiratory distress and a high fever. Frank had diabetes mellitus and had smoked for 25 years. His white blood count was 24,000/µl and his C-reactive protein was 24 mg/ml, both signs that his immune system was fighting an infection. ▪ His chest X-ray showed an abnormal shadow, and his chest CT scan showed thickened bronchial walls. He was coughing up black sputum. ▪ The physician prescribed an antibiotic, cefotiam hydrochloride, but Frank’s condition worsened. 26 Case History: Fungus Growing in the Lung – 2 ▪ By the tenth day he was producing 100 ml of sputum a day, and the CT scan of his lung showed multiple lesions (clouded regions). Since antibacterial antibiotics had failed, Frank was tested for fungi. A culture of his sputum and PCR amplification of fungal DNA revealed the fungus Aspergillus fumigatus. Frank was treated with the antifungal agents itraconazole, meropenem trihydrate, and amphotericin B, but he died on the 25th day. 27 Questions?