Transcript Document
Chapter 12 Characterizing and Classifying Eukaryotes 10/1/11 MDufilho 1 General Characteristics of Eukaryotic Organisms • Five major groups – – – – – Protozoa Fungi Algae Water molds Slime molds • Include both human pathogens and organisms vital for human life 10/1/11 MDufilho 2 Protozoa • Diverse group defined by three characteristics – Eukaryotic – Unicellular – Lack a cell wall • Motile by means of cilia, flagella, and/or pseudopodia – Except subgroup, apicomplexans 10/1/11 MDufilho 3 Protozoa • Distribution of Protozoa – Require moist environments – Most live in ponds, streams, lakes, and oceans – Critical members of plankton – Others live in moist soil, beach sand, and decaying organic matter – Very few are pathogens 10/1/11 MDufilho 4 Protozoa • Morphology of Protozoa – Great morphologic diversity – Some have two nuclei – Macronucleus – Contains many copies of the genome – Micronucleus – Variety in number and kinds of mitochondria – Some have contractile vacuoles – All produce trophozoites; some produce cysts 10/1/11 MDufilho 5 Protozoa • Nutrition of Protozoa – Most are chemoheterotrophic – Obtain nutrients by phagocytizing bacteria, decaying organic matter, other protozoa, or the tissues of host – Few absorb nutrients from surrounding water – Dinoflagellates and euglenoids are photoautrophic 10/1/11 MDufilho 6 Protozoa • Reproduction in Protozoa – Most reproduce asexually only – Binary fission or schizogony – Few also have sexual reproduction – Some become gametocytes that fuse with one another to form diploid zygotes – Some utilize a process called conjugation 10/1/11 MDufilho 7 Protozoa • Classification of Protozoa – Based on 18S rRNA and features visible by electron microscopy – One scheme classifies into six taxa 10/1/11 © 2012 Pearson Education Inc. MDufilho 8 Classification of Protozoa Parabasala • lack mitochondria, but each • has a single nucleus and a parabasal body, which is a Golgi-like structure. • Trichomonas, can cause severe inflammation of the human vagina. 10/1/11 MDufilho 9 Protozoan STDs • Trichomoniasis – Signs and symptoms – Females have vaginal discharge and vaginal irritation – Males are typically asymptomatic – Pathogen and virulence factors – Caused by Trichomonas vaginalis – Pathogenesis and epidemiology – Transmission primarily via sexual intercourse – Most common curable STD in women – Trichomoniasis increases risk of infection by HIV 10/1/11 MDufilho 10 Figure 24.14 Trichomonas vaginalis Flagella 10/1/11 Undulating membrane MDufilho 11 Protozoan STDs • Trichomoniasis – Diagnosis, treatment, and prevention – Diagnose by presence of Trichomonas in clinical samples – Treat with a single dose of oral metronidazole – Prevent by avoiding sexual intercourse with infected persons 10/1/11 MDufilho 12 Protozoa • Classification of Protozoa – Diplomonadida – Lack mitochondria, Golgi bodies, peroxisomes – Prominent example is Giardia 10/1/11 MDufilho 13 Protozoan Diseases of the Intestinal Tract • Giardiasis – Signs and symptoms – Often asymptomatic – Diarrhea and associated symptoms can last up to four weeks – Pathogen and pathogenesis – Caused by Giardia intestinalis – G. intestinalis interferes with intestinal absorption, causing flatus and fever 10/1/11 MDufilho 14 Figure 23.16 Trophozoites of Giardia intestinalis Intestinal villi 10/1/11 Ventral adhesive disk Mark left by adhesive disk MDufilho Dorsal surface 15 Protozoan Diseases of the Intestinal Tract • Giardiasis – Epidemiology – Infection results from ingesting cysts in contaminated water – Hikers and campers are at particular risk – Diagnosis, treatment, and prevention – Diagnosed by microscopic observation of Giardia in stool – Treat with metronidazole (adults) or furazolidone (children) 10/1/11 MDufilho 16 Protozoan Diseases Euglenozoa • photoautotrophic, unicellular microbes with chloroplasts • Store food as a unique polysaccharide called paramylon instead of as a starch. • Have a semi-rigid, proteinaceous, helical pellicle to maintain shape. • Some kinetoplastids have a single large mitochondrion that contains a unique region of DNA called a kinetoplast. • Trypanosoma and Leishmania, are pathogenic 10/1/11 . MDufilho 17 Protozoan Diseases of the Nervous System • African Sleeping Sickness – Signs and symptoms – Three clinical stages – Site of bite becomes lesion – Parasites in the blood create fever, lymph node swelling, and headache – Meningoencephalitis results when protozoa invade the CNS – Pathogen and virulence factors – Caused by Trypanosoma brucei – Evades immune system by changing surface glycoproteins 10/1/11 MDufilho 18 Figure 20.17 The life cycle of Trypanosoma brucei Trypomastigotes reproduce by binary fission, becoming epimastigotes in midgut of tsetse fly. Epimastigotes migrate to salivary glands. Glossina (tsetse fly) Trypanosoma epimastigote matures into infective trypomastigote within salivary gland of tsetse fly. Trypomastigotes are ingested by tsetse fly during blood meal. Tsetse fly injects trypomastigotes while feeding. Some trypomastigotes invade central nervous system. Trypomastigotes are carried via bloodstream to other sites. Trypomastigotes multiply by binary fission in bodily fluids, including blood, lymph, and spinal fluid. 10/1/11 MDufilho 19 Protozoan Diseases of the Nervous System • African Sleeping Sickness – Diagnosis, treatment, and prevention – Diagnosed by microscopic observation of trypanosomes in blood, lymph, or spinal fluid – Alternatively, tissue biopsy may be done – Treatment based on disease stage – Melarsoprol – if in brain – Pentamidine and suramin – early stages – Insecticide application can help reduce occurrence 10/1/11 MDufilho 20 Protozoan and Helminthic Cardiovascular and Systemic Diseases • Chagas’ Disease – Signs and symptoms – Swelling at infection site in followed by nonspecific symptoms – Chronic manifestations can occur many years after infection – Pathogen and virulence factors – Caused by Trypanosoma cruzi – Endemic throughout Central and South America – Most mammals can harbor T. cruzi 10/1/11 MDufilho 21 Figure 21.21 The life cycle of Trypanosoma cruzi in a South American Epimastigotes transform into trypomastigotes in hindgut of kissing bug. Trypomastigotes form epimastigotes by binary fission in midgut of kissing bug. Triatoma (kissing bug, life size) Trypomastigotes are deposited in feces of kissing bug at bite wound site. Trypomastigotes are ingested by kissing bug during blood meal. Scratching introduces trypomastigotes into blood. Trypomastigotes travel in blood, penetrate cells, and transform into amastigotes. Some amastigotes transform into trypomastigotes in blood. Amastigotes multiply by binary fission in cells and infected tissue. Some amastigotes infect other cells. 10/1/11 MDufilho 22 Protozoan and Helminthic Cardiovascular and Systemic Diseases • Chagas’ Disease – Pathogenesis and epidemiology – Transmitted through the bite of infected Triatoma or transfusion with infected blood – Progresses through four stages over several months – Diagnosis, treatment, and prevention – Diagnosed by microscopic identification of T. cruzi or xenodiagnosis – Prevention involves avoidance of Triatoma bugs 10/1/11 MDufilho 23 Parasitic Infestations of the Skin • Leishmaniasis – Signs and symptoms – Cutaneous: Produces large painless skin lesions – Mucocutaneous: Skin lesions enlarge to encompass mucous membranes – Visceral: Parasite is spread by macrophages throughout body – Pathogen and virulence factors – Leishmania is the causative agent – Protozoan transmitted to humans by female sand flies 10/1/11 MDufilho 24 Figure 19.24 Mucocutaneous leishmaniasis 10/1/11 MDufilho 25 Parasitic Infestations of the Skin • Leishmaniasis – Pathogenesis and epidemiology – Infected macrophages stimulate inflammatory responses – Leishmaniasis endemic in parts of the tropics and subtropics – Diagnosis, treatment, and prevention – Diagnosed by microscopic identification of the protozoa – Most cases heal without treatment – Antimicrobials are needed for severe infections – Prevention involves reducing exposure to the reservoir host 10/1/11 MDufilho 26 Protozoan Diseases Alveolates • have cavities called alveoli beneath their cell surfaces. They include ciliates, which have cilia and two nuclei. Paramecium is a wellknown pond-water ciliate. • The alveolates called apicomplexans are all pathogens of animals. – The name of this group refers to the complex of special intracellular organelles that enables them to penetrate a host cell. – Plasmodium, Cryptosproidium, Toxoplasma 10/1/11 . MDufilho 27 Protozoan and Helminthic Cardiovascular and Systemic Diseases • Malaria – Signs and symptoms – Associated with parasite’s life cycle within erythrocytes – Fever and chills occur on a 2- to 3-day cycle – Anemia, weakness, fatigue – Pathogens – Four Plasmodium species cause malaria – Disease severity depends on the species 10/1/11 MDufilho 28 Figure 21.19 The life cycle of Plasmodium Oocyst forms sporozoites, ruptures, and sporozoites migrate to salivary glands of mosquito. Zygote differentiates into ookinete, which becomes an oocyst in gut wall. Anopheles mosquito Gametocytes become gametes that fuse to form zygote. Oocyst Sporogonic phase Sporozoites Mosquito ingests gametocytes during blood meal. Sporozoites are injected into host during blood meal. Gametocytes in blood cells Some merozoites develop into gametocytes within erythrocytes. Sporozoites invade liver cells and undergo schizogony. Exoerythrocytic phase Erythrocytic cycle A merozoite becomes a trophozoite. 10/1/11 Liver cell ruptures and releases numerous merozoites into blood. Trophozoites undergo schizogony to produce merozoites, which are released. Free merozoites penetrate MDufilho erythrocytes. Merozoites 29 Protozoan and Helminthic Cardiovascular and Systemic Diseases • Malaria – Virulence factors – Reproductive cycle hides parasite from immune surveillance – Malaria secretome injects toxins into host cells – Adhesins allow red blood cells to adhere to certain tissues – Merozoites form within vesicles and avoid detection – Changes in body chemistry attract other mosquitoes 10/1/11 MDufilho 30 Protozoan and Helminthic Cardiovascular and Systemic Diseases • Malaria – Pathogenesis – P. falciparum causes the most severe malaria – Certain genetic traits can increase resistance to malaria – Epidemiology – Endemic throughout tropics and subtropics – Diagnosis, treatment, and prevention – Diagnosis made by identifying Plasmodium in blood – Treatment varies by species and disease severity – Some Plasmodium strains resistant to antimalarial drugs – Prevention requires control of mosquitoes 10/1/11 MDufilho 31 Protozoan and Helminthic Cardiovascular and Systemic Diseases • Toxoplasmosis – Signs and symptoms – Majority of cases have no symptoms – Symptoms in individuals with poor immunity – Fever, malaise, inflammation of the lungs, liver, and heart – Symptoms in the fetus – Stillbirth, epilepsy, mental retardation – Pathogen and virulence factors – Toxoplasma gondii is the causative agent – Cats are the definitive host 10/1/11 MDufilho 32 Figure 21.20 The life cycle of Toxoplasma gondii Pseudocysts are ingested by cat in wild prey or undercooked meat. Sporozoites invade tissue, developing into bradyzoites within cells. Masses of bradyzoites become pseudocysts. Sexual reproduction of parasite occurs in cat’s digestive system, and immature oocysts are shed in cat feces. Oocyst produces internal sporozoites. Oocysts are ingested by rodent, or accidentally by another animal or human. Pseudocysts are ingested by humans in undercooked meat. 10/1/11 Sporozoites invade tissue, developing into bradyzoites and MDufilho forming pseudocysts. 33 Protozoan and Helminthic Cardiovascular and Systemic Diseases • Toxoplasmosis – Pathogenesis and epidemiology – Consumed in undercooked meat containing the parasite – Transmission across the placenta can also occur – Specific mechanism of disease is not yet known – Diagnosis, treatment, and prevention – Diagnosed mainly by detecting organisms in tissues – Treatment needed only in AIDS patients, pregnant women, and newborns – Prevention is difficult because T.gondii has numerous hosts 10/1/11 MDufilho 34 Protozoan Diseases of the Intestinal Tract • Cryptosporidiosis – Signs and symptoms – Severe watery diarrhea with potentially serious complications – Pathogen and pathogenesis – Caused by Cryptosporidium parvum – Pathogenicity of C. parvum unclear – Epidemiology – Infection results from drinking contaminated water – Diagnosis, treatment, and prevention – Treated with fluid and electrolyte replacement – Prevented with proper hygiene 10/1/11 MDufilho 35 Figure 23.17 Oocysts of Cryptosporidum parvum in feces Oocysts 10/1/11 MDufilho 36 Protozoan Diseases Amoebozoa • lobe-shaped pseudopodia and no shells. • The normally free-living amoebae Naegleria and Acanthamoeba can each cause disease of the brains in humans and animals that swim in water containing them. • Entamoeba causes potentially fatal dysentery. 10/1/11 . MDufilho 37 Protozoan Diseases of the Nervous System • Primary Amebic Meningoencephalopathy – Signs and symptoms – Same as those of meningitis and encephalitis caused by other microbes – Pathogen, pathogenesis, and epidemiology – Caused by Acanthamoeba and Naegleria – Enter host through abrasions on the skin or the eyelid or by inhalation of contaminated water – Diagnosis, treatment, and prevention – Drugs have limited success – Prevented by avoiding possibly contaminated water supplies 10/1/11 MDufilho 38 Protozoan Diseases of the Intestinal Tract • Amebiasis – Signs and symptoms – Luminal amebiasis is asymptomatic – Invasive amebic dysentery causes severe diarrhea, colitis, appendicitis – Invasive extraintestinal amebiasis causes necrotic lesions in various organs – Pathogen, virulence factors, and pathogenesis – Caused by Entamoeba histolytica – Trophozoites in the peritoneal cavity or blood cause symptoms 10/1/11 MDufilho 39 Disease at a Glance 23.9a Amebiasis: course of infection Person consumes cysts of Entamoeba histolytica, usually from contaminated water. Excystment in small intestine releases trophozoites. Trophozoites multiply in large intestine and attach to intestinal lining, causing luminal amebiasis. They may invade the peritoneum to cause amebic dysentery. They may invade the bloodstream to be carried throughout the body. They cause invasive extraintestinal amebiasis when they infect the liver, lungs, spleen, kidneys, or brain, and they may cause death. Cysts are shed in stool. 10/1/11 MDufilho 40 Protozoan Diseases of the Intestinal Tract • Amebiasis – Epidemiology – Transmitted by consumption of contaminated food or water, from contaminated hands, or oral-anal intercourse – Majority of individuals develop luminal amebiasis – Diagnosis, treatment, and prevention – Diagnosed by microscopic observation of Entamoeba in stool or intestinal biopsy – Treat with oral rehydration therapy and antiamebic drugs – Prevent with proper hygiene and safe sex practices 10/1/11 MDufilho 41 Fungi • Chemoheterotrophic • Have cell walls typically composed of chitin • Do not perform photosynthesis – Lack chlorophyll • Related to animals 10/1/11 MDufilho 42 Fungi • The Significance of Fungi – Decompose dead organisms and recycle their nutrients – Help plants absorb water and minerals – Used for food and in manufacture of foods and beverages – Produce antibiotics – Serve as important research tools – 30% cause diseases of plants, animals, and humans – Can spoil fruit, pickles, jams, and jellies 10/1/11 MDufilho 43 Figure 12.15 Fungal morphology-overview 10/1/11 MDufilho 44 Fungi • Nutrition of Fungi – Acquire nutrients by absorption – Most are saprobes – Haustoria allow some to derive nutrients from living plants and animals – May use ionizing radiation as energy source – Most fungi are aerobic – Many yeasts are facultative anaerobes 10/1/11 . MDufilho 45 Fungi • Reproduction in Fungi – All have some means of asexual reproduction involving mitosis and cytokinesis – Most also reproduce sexually – Budding and asexual spore formation – Yeasts bud in manner similar to prokaryotic budding – Pseudohypha – Series of buds that remain attached to one another and to parent cell – Filamentous fungi produce lightweight spores that disperse over large distances 10/1/11 MDufilho 46 Figure 12.18 Representative asexual spores of molds-overview 10/1/11 MDufilho 47 Fungi • Classification of Fungi – – – – Division Zygomycota Division Ascomycota Division Basidiomycota Deuteromycetes 10/1/11 MDufilho 48 Fungi Division Zygomycota • Most are saprobes. • Form rough-walled sexual structures called zygosporangia • Microsporidia are zygomycetes that are obligate intracellular parasites, some of which are known to cause disease in immunocompromised persons. 10/1/11 MDufilho 49 Fungi Division Ascomycota • Form haploid ascospores within sacs called asci. • Ascomycetes include – most of the fungi that spoil food, as well as – plant pathogens - Dutch elm disease – Many human pathogens( Aspegillosis in humans and many others). • Beneficial in baking and brewing(Saccharomyces), research, and pharmaceuticals (penicillium). 10/1/11 MDufilho 50 Mycoses of the Hair, Nails, and Skin • Mycoses are diseases caused by fungi • Most are opportunistic pathogens • Mycoses are classified by infection location – Superficial – occur on the hair, nails, and outer skin layers; most common fungal infections – Subcutaneous – in the hypodermis and muscles – Systemic – affect numerous systems 10/1/11 MDufilho 51 Mycoses of the Hair, Nails, And Skin • Superficial Mycoses – Signs and symptoms – Piedra – Irregular nodules on the hair shaft – Pathogens and virulence factors – Piedraia hortae causes black piedra – Trichosporon beigelii causes white piedra 10/1/11 MDufilho 52 Figure 19.17 Black piedra 10/1/11 MDufilho 53 Mycoses of the Hair, Nails, And Skin • Superficial Mycoses – Pathogenesis and epidemiology – Superficial fungi produce keratinase, which dissolves keratin – Fungi often transmitted via shared hair brushes and combs – Diagnosis, treatment, and prevention – Piedra diagnosed by appearance and treated by shaving infected hair 10/1/11 MDufilho 54 Mycoses of the Hair, Nails, And Skin • Cutaneous Mycoses – Some fungi that grow in the skin manifest as cutaneous lesions – Dermatophytoses are cutaneous infections caused by dermatophytes – Cell-mediated immune responses damage deeper tissues – Called tineas by location 10/1/11 MDufilho 55 Figure 19.20 Athlete’s foot 10/1/11 MDufilho 56 Figure 19.19 Dermatophytosis (ringworm) 10/1/11 MDufilho 57 Table 19.5 Common Dermatophytoses 10/1/11 MDufilho 58 Mycoses of the Hair, Nails, And Skin • Cutaneous Mycoses – Diagnosis, treatment, and prevention – Diagnosed by clinical observation – KOH preparation of skin or nail samples confirms diagnosis – Limited infections treated with topical agents – Widespread infections treated with oral drugs 10/1/11 MDufilho 59 Mycoses of the Hair, Nails, and Skin • Wound Mycoses – Some fungi grow in deep tissues but do not become systemic – Fungi eventually grow into the epidermis to produce skin lesions 10/1/11 MDufilho 60 Mycoses of the Hair, Nails, and Skin • Wound Mycoses – Chromoblastomycosis – Caused by four species of ascomycete fungi – Painless lesions that progressively worsen – Phaeohyphomycosis – Caused by over 30 genera of fungi – Acquired when spores enter wounds 10/1/11 MDufilho 61 Figure 19.21 A leg with extensive lesions of chromoblastomycosis 10/1/11 MDufilho 62 Mycoses of the Hair, Nails, and Skin • Wound Mycoses – Mycetomas – Caused by several genera of soil fungi – Tumorlike lesions on skin, fascia, and bones – Treatment combines surgery and antifungal therapy with ketoconazole for one to three years 10/1/11 MDufilho 63 Figure 19.22 A mycetoma of the ankle 10/1/11 MDufilho 64 Mycoses of the Hair, Nails, and Skin • Wound Mycoses – Sporotrichosis – gardener’s disease – Caused by a dimorphic ascomycete – Subcutaneous infection usually limited to the arms and legs – Occurs as fixed cutaneous or lymphocutaneous sporotrichosis 10/1/11 MDufilho 65 Figure 19.23 Lymphocutaneous sporotrichosis on the arm 10/1/11 MDufilho 66 Mycoses of the Nervous System • Mycoses of the Nervous System – Spread from the lungs to the CNS via the blood – Mushroom toxins can produce hallucinations and neurological problems – May also produce fungal meningitis 10/1/11 . MDufilho 67 Mycoses of the Nervous System • Cryptococcal Meningitis – Systemic – Signs and symptoms – Similar to those of bacterial meningitis – Pathogen and virulence factors – Cryptococcus neoformans is causative agent – Two variants of the yeast found worldwide – Resists phagocytosis by defensive cells 10/1/11 MDufilho 68 Mycoses of the Nervous System • Cryptococcal Meningitis – Pathogenesis and epidemiology – Infections follows inhalation of spores or dried yeast cells – Occurs in terminal AIDS patients and in transplant recipients – Diagnosis, treatment, and prevention – Diagnosed by detection of fungal antigen in CSF – Treated with intravenous antifungal drugs 10/1/11 MDufilho 69 Mycoses of the Lower Respiratory System • Coccidioidomycosis – (valley fever, desert fungus) – Signs and symptoms – Resembles pneumonia or tuberculosis – Can become systemic in immunocompromised persons – Pathogen and virulence factors – Caused by Coccidioides immitis – Pathogen assumes yeast form at human body temperature – Pathogenesis – Arthroconidia from the soil enter the body through inhalation 10/1/11 MDufilho 70 Figure 22.18 Coccidioidomycosis lesions in subcutaneous tissue 10/1/11 MDufilho 71 Figure 22.19 Spherules of Coccidioides immitis Spherule 10/1/11 MDufilho Spores 72 Mycoses of the Lower Respiratory System • Coccidioidomycosis – Epidemiology – Almost exclusively in southwestern U.S. and northern Mexico – Diagnosis, treatment, and prevention – Diagnosed by presence of spherules in clinical specimens – Treat with amphotericin B – Protective masks can prevent exposure to arthroconidia 10/1/11 MDufilho 73 Mycoses of the Lower Respiratory System • Blastomycosis – Signs and symptoms – Flulike symptoms – Systemic infections can produce lesions on the face and upper body or purulent lesions on various organs – Pathogen – Caused by Blastomyces dermatitidis – Pathogenic yeast form at human body temperature 10/1/11 MDufilho 74 Figure 22.20 Cutaneous blastomycosis in an American woman 10/1/11 MDufilho 75 Mycoses of the Lower Respiratory System • Blastomycosis – Pathogenesis and epidemiology – Enters body through inhalation of dust carrying fungal spores – Incidence of human infection is increasing – Diagnosis, treatment, and prevention – Diagnosis based on fungus identification in clinical samples – Treated with amphotericin B – Relapse common in AIDS patients 10/1/11 MDufilho 76 Mycoses of the Lower Respiratory System • Histoplasmosis – Signs and symptoms – Asymptomatic in most cases – Symptomatic infection causes coughing with bloody sputum or skin lesions – Pathogen – Caused by Histoplasma capsulatum – Pathogenic yeast form at human body temperature 10/1/11 MDufilho 77 Mycoses of the Lower Respiratory System • Histoplasmosis – Pathogenesis and epidemiology – Humans inhale airborne spores from the soil – Prevalent in the eastern U.S. – Diagnosis, treatment, and prevention – Diagnosis based on fungus identification in clinical samples – Infections in immunocompetent individuals typically resolve without treatment 10/1/11 . MDufilho 78 Mycoses of the Lower Respiratory System • Pneumocystis Pneumonia (PCP) – Signs and symptoms – Difficulty breathing, anemia, hypoxia, and fever – Pathogen – Caused by Pneumocystis jirovecii – Pathogenesis and epidemiology – Transmitted by inhalation of droplets containing the fungus – Common disease in AIDS patients – Diagnosis, treatment, and prevention – Diagnosis based on clinical and microscopic findings – Treat with trimethoprim and sulfamethoxazole – Impossible to prevent infection with P. jirovecii 10/1/11 MDufilho 79 Figure 22.21 Cysts of Pneumocystis jirovecii in lung tissue Cyst 10/1/11 MDufilho 80 Figure 22.17 The geographic distributions of three systemic fungal diseases endemic to North America Coccidioidomycosis 10/1/11 Blastomycosis MDufilho Histoplasmosis 81 Fungi Division Basidiomycota • Mushrooms and other fruiting bodies of basidiomycetes, produce projections called basidia, the ends of which produce sexual basidiospores. • Most basidiomycetes decompose cellulose and lignin in dead plants and return nutrients to the soil. • Many produce hallucinatory chemicals or toxins • Cryptococcus neoformans – human pathogen 10/1/11 MDufilho 82 Fungi Division Deuteromycetes • The deuteromycetes, formerly classified in the division Deuteromycota, are an informal grouping of fungi having no known sexual stage. • Recently, the analysis of rRNA sequences has revealed that most deuteromycetes belong in the division Ascomycota, • and thus modern taxonomists have abandoned Deuteromycota as a formal taxon. 10/1/11 MDufilho 83