Chapter 12: Fungi, Algae, Protozoa, and Multicellular Parasites

Transcription

1 Chapter 12: Fungi, Algae, Protozoa, and Multicellular Parasites

2 Fungi Mycology = Study of Fungi All Fungi are chemoheterotrophs Require organic compounds for energy and carbon Can be aerobic (filamentous, bread mold) or facultative anaerobes (yeast) Most of the 100,000 or more fungal species are decomposers of dead plant material. Very few organisms other than fungi have enzymes that can breakdown hard plant material (cellulose, lignin, pectins) Only about 200 species are implicated in human disease.

3 Table 12.1

4 Table 12.2

5 Fungi: Vegetative Structures (cells involved in catabolism and growth) Multicellular fungi, unlike yeast identification, are identified on the basis of physical appearance, including colony characteristics and reproductive spores. 1. Molds and Flesh Fungi a. Thallus long filaments of cells joined together (called hyphae). Color, consistency of growth. b. Septa cross-walls dividing the hyphae into distinct, uninucleate cell like units (called septate hyphae) c. Vegetative hyphae portion that is used to obtain nutrients (growthbelow surface of media) d. Aerial hyphae projects above media on which fungus is growing and often contains spores e. Mycelium filamentous mass

6 Figure Overview

7 Figure Overview

8 Fungi: Vegetative Structures 2. Yeasts Nonfilamentous unicellular fungi that are spherical or oval Some divide by fission that can either be even or uneven cell division (budding) Candida albicans sometimes produces buds that fail to detach into daughter cells and are called pseudohyphae. These can resemble hyphae and penetrate deeper tissue. Colonies on agar can resemble bacterial colonies, especially staph colonies. Can use oxygen or organic compounds as final electron acceptor (can do aerobic respiration and fermentation)

9 Figure 12.3

10 Figure 21.17: Candidiasis - Overview. Chlamydoconidia Pseudohyphae Blastoconidia (a) Candida albicans 20 mm (b) Oral candidiasis, or thrush

11 Fungi: Vegetative Structures 3. Dimorphic Fungi Some fungi, especially pathogenic fungi, exhibit two forms of growth yeastlike at 37 0 C and moldlike at 25 0 C Examples of human pathogens that are dimorphic Histoplasma capsulatum Coccidioides immitis, Valley Fever

12 Figure 12.4

13 Figure 24.19, steps 4 6: The life cycle of Coccidioides immitis, the cause of coccidioidomycosis. Inhaled arthroconidium enlarges and begins to develop into a spherule. Released endospores spread in tissue each developing into new spherule Human Spherule in tissue (about 30 µm in diameter) Endospores develop within spherule. Spherule releases endospores.

14 Fungi: Life Cycle 1. Can reproduce asexually by fragmentation of hyphae 2. Sexual spores result from fusion of nuclei from two opposite mating strains of the same species of fungi. Not as common as asexual reproduction. Used to classify fungus into 4 divisions.

15 Fungi: Life Cycle 3. Asexual spores upon germination are identical to parent (clones) Used commonly to identify fungus microscopically in laboratories a. Conidiospore A unicellular or multicellular spore that is not enclosed in a sac. Are usually produced in a chain at the end of a conidiophore. (Example: Aspergillis) Another type of conidiospore is an arthrospore formed by fragmentation of a septate hypha into single, slightly thickened cells. (Example: Coccidioides immitis) Another type of conidiospore is a blastospore bud comes off parent cell (Example: Cryptococcus) b. Chlamydospore a thick-walled spore formed by rounding and enlarging within a hyphal segment. Example: Candida albicans c. Sporangiospore A spore formed within a sporangium or sac at the end of aerial hyphae. (Example: Rhizopus)

16 Figure 12.5a

17 Figure 12.5b

18 Figure 12.5c

19 Figure 12.5d

20 Figure 12.5e

21 Fungi: Nutritional Adaptations Differ from bacteria in the following ways: 1. Grow best at ph Almost all molds are aerobic; most yeast are facultative anaerobes 3. Most fungi are more resistant to osmotic pressure (can grow in high sugar or salt concentration) 4. Fungi can grow on substances with low moisture 5. Require less nitrogen than bacteria

22 Fungi: Medically Important Division of Fungi 4 groups: 3 sexual (perfect fungi), 1 asexual (imperfect fungi) 1. Anamorphs (Deuteromycota, fungi imperfecti) Placed here if they have not been found to produce sexual spores (telomorph); produce asexual chlamydospores, arthrospores, conidiospores, or budding. Have septate hyphae. Most are anamorph (asexual) phases of Ascomycota and a few are Basidiomycota. Example: Coccidioides immitis 2. Zygomycota Saprophytic molds that have nonseptate hyphae and produce sporangiospores (asexual) and zygospores (sexual) Life cycle: Sexual spores are zygospore A large spore enclosed in a thick wall. Examples: Mucor and Rhizopus

23 Figure Overview

24 Fungi: Medically Important Division of Fungi 3. Ascomycota Includes molds with septate hyphae and some yeast. Life cycle Asexual spores are usually conidiospores produced in long chains from the cinidiophore. Sexual spore = ascus with ascospores Examples: Aspergillus and Histoplasma capsulatum 4. Basidiomycota Mushrooms Life cycle: Have septate hyphae and produce basidiospores; some produce conidiospores. Example: Cryptococcus neoformans (anamorph)

25 Figure Overview

26 Figure Overview

27 Figure Overview

28 Fungi: Fungal Diseases 1. Systemic mycoses are fungal infections deep within the body and affect many tissues and organs. Examples: Histoplasmosis and Coccidioidomycosis 2. Subcutaneous mycoses are fungal infections beneath the skin. Example: Sporothrix schenckii (rose thorns) 3. Cutaneous mycoses (dermatophytes) affect keratin-containing tissues such as hair, nails, and skin. Example: Microsporum (ringworm) 4. Opportunistic mycoses are caused by normal microbiota or fungi that are not usually pathogenic. Mucormycosis (Rhizopus and Mucor) Aspergillosis (Aspergillis) Candidiasis (Thrush) Candida albicans

29 Fungi: Economic Effect of Fungi Undesirable effects 1. Spoilage of food. Grow where bacteria cannot. Fruit, grains, vegetables, jams/jellies 2. Plant pathogens Benefits Dutch elm disease carried by bark beetles devastated US tree population Chestnut blight imported from China (1904) killed nearly all chestnut trees in US 3. Saccharomyces cerevisiae Used to make bread, wine and beer. Genetically engineered protein products e.g. Hepatitis B vaccine Biological control of pests. Medications such as anticancer drug taxol.

30 Protozoa A. Definition Unicellular, eukaryotic, chemoheterotrophic organisms that belong to the Kingdom Protista. Usually inhabit water and soil. About 20,000 known species. B. Characteristics 1. Life Cycle reproduce asexually by fission, budding, or schizogony Schizogony is a form of division where the nucleus divides many times before the cell divides. Then a small portion of the cytoplasm forms around each nuclei. This is typical in malaria. 2. Encystment some produce a cyst for protection during adverse environmental conditions. Loss of moisture in feces transforms trophozoite to a cyst. Sometimes you don t see troph in feces, just cyst. The cyst form allows for survival outside the host organism. 3. Nutrition Usually aerobic heterotrophs (may be anaerobic in gut) and the vegetative stage (trophozoite) feeds upon bacteria and small particulate nutrients. Digestion takes place in membrane-enclosed vacuoles.

31 Protozoa C. Medically Important Phyla Phyla classification based on rrna sequencing 1. Phylum Archaezoa: eukaryotes that lack mitochondria. Often spindle shaped with 2 or more flagella acting as a whip projecting from front end for locomotion. Many live as symbionts in animal guts. Examples: Trichomonas vaginalis Has no cyst so must be transmitted quickly and shows undulating membrane. Found in vagina and male urinary tract. Transmitted sexually. Giardia lamblia Found in small intestine of humans and other animals. Causes giardiasis Chilomastix found in human intestine. Mildly pathogenic to symbiont.

32 Figure 12.17b

33 Figure 12.17c

34 Figure 12.17d

35 Figure 12.17a

36 Protozoa: Medically Important Phyla 2. Phylum Microsporans Like Archaezoa they lack mitochondria. They are obligate intracellular parasites that have microtubules. Causes chronic diarrhea and keratoconjunctivitis usually in AIDS patients. 3. Phylum Rhizopoda Amoeba that move by extending blunt, lobe-like projections of cytoplasm called pseudopods. Exampel: Entamoeba histolytica (Amoebic dysentery) Example: Acanthamoeba Grows in tap water and infects cornea and may cause blindness

37 Figure Overview

38 Cornea clouding due to Acanthamoeba Acanthamoeba in corneal scraping

39 Protozoa: Medically Important Phyla 4. Phylum Apicomplexa Apicomplexans are non-motile in mature forms and are obligate intracellular parasites. Have organelles at the tips of their cells that contain enzymes that allow them to enter the host s tissues. Have complex life cycle with transfer between multiple hosts. Examples: Plasmodium vivax Causes malaria via a mosquito vector. Babesia microti Causes fever and anemia in immunosuppressed individuals via a tick vector. Toxoplasma gondii Life cycle involves domestic cat. Dangerous to pregnant women as it can cause congenital infection of fetus in utero. Cryptosporidium Newly recognized. Found in AIDS and other immunocompromised individuals where it can cause respiratory or gallbladder infections or possibly death. Cause mild intestinal illness in immunocompetant individuals. Water borne transmission. Cyclospora similar to Cryotosporidium Causes diarrhea. An emerging pathogen.

40 Figure Overview

41 Cerebral T. gondii encephalitis in a patient with AIDS Unstained oocysts of Toxoplasma in stool

42 Protozoa: Medically Important Phyla 5. Ciliates (Phylum ciliophora) Have cilia arranged on precise rows that are shorter than flagella and move in unison to propel the cell Example: Paramecium, a common puddle dweller Example: Balantidium coli causative agent of severe dysentery 6. Phylum Euglenozoa: flagellated cells with disk-like mitochondria and absence of sexual reproduction. Hemoflagellates: Transmitted by the bites of blood-feeding insects and are found in the circulatory system of the bitten host. They have long slender bodies and an undulating membrane suited to life in a viscous fluid. Genus Trypanosoma T. brucei gambiense transmitted by tsetse fly, causes African Sleeping sickness T. cruzi transmitted by the kissing bug and is causative agent of Chagas disease Naegleria fowleri Infects brain of humans swimming in infested warm water via mucous membrane exposure

43 Figure Overview

44 Figure 12.16

45 Figure 23.22: Trypanosoma cruzi, the cause of Chagas' disease (American trypanosomiasis). 2.5 µm

46 Naegleria trohpozoites in experimentally infected mouse brain

47 Helminths A. Characteristics Multicellular, eukaryotic animals that generally possess digestive, circulatory, nervous, excretory, and reproductive systems. Following generalizations distinguishes parasitic helminths from free-living relatives: May lack a digestive tract. Absorb nutrients from host. Reduced nervous system (don t need it) Reduced or lack locomotion system Reproductive system is complex with production of large numbers of eggs B. Life cycle Very complex Adult stage (sexual) is found in the definitive host Each larval stage requires an intermediate host Helminths can be monoecious (hermaphroditic) or dioecious (separate sexes)

48 Helminths: Platyhelminthes Phylum Platyhelminthes Flattened worms, front to back 2 classes: trematodes and cestodes 1. Class Trematodes Flukes Have an oral and ventral sucker which attaches to host Given common names according to tissue in which they live.» Example: Clonorchis sinensis Liver fluke Occurs in Asia

49 Helminths: Phylum Platyhelminthes: Class trematodes Trematode life cycle example: Clonorchis sinensis, the liver fluke Eggs of trematodes hatch into free-swimming miracidia that enter the first intermediate host Two generations of rediae (molting) develop in the first intermediate host The rediae become cercariae that bore out of the first intermediate host and penetrate the second intermediate host Cercariae encyst as metacercariae in the second intermediate host After they are ingested by the definitive host, the metacercariae develop into adults.

50 Clonorchis senensis life cycle

51 Helminths: Phylum Platyhelminthes: Class trematodes Trematode life cycle example #2 Paragonimus westermani Lung fluke Occurs throughout the world including US and Canada» Life cycle Eggs of trematodes hatch into free-swimming miracidia that enter the first intermediate host Two generations of rediae develop in the first intermediate host The rediae become cercariae that bore out of the first intermediate host and penetrate the second intermediate host Cercariae encyst as metacercariae in the second intermediate host After they are ingested by the definitive host, the metacercariae develop into adults Lab diagnosis made by finding fluke eggs in sputum and feces

52 Paragonimus westermani (lung fluke) life cycle Figure Overview

53 Helminths: Phylum Platyhelminthes 2. Class Cestodes Tapeworms The head (scolex) has suckers (hooks) for attaching to host Body consists of segments called proglottids which are continuously produced at the neck region. Each contains male and female reproductive organs The ones farthest from the neck are the mature ones which contain fertilized eggs» These eggs infect the proper intermediate host Humans become definitive hosts after eating an intermediate host with larval infestations.

54 General anatomy of an adult cestode (tape worm) Figure Overview (1 of 3)

55 Helminths: Phylum Platyhelminthes: Class Cestodes Tapeworms Example: Taenia saginata Beef tapeworm Humans are the definitive host Organism can reach 6m Cattle are intermediate hosts As mature proglottids (with eggs) are excreted from humans they wiggle away and are ingested by cattle The larvae hatch and bore through the intestinal wall and then migrate to muscle and then are ingested by humans again Lab diagnosis is made by seeing mature proglottids and eggs in feces

56 Helminths: Phylum Platyhelminthes: Class Cestodes Tapeworms Example: Taenia solium Pork tapeworm Adult worms living in human intestines produce eggs which pass in the feces Eggs are then eaten by pigs, where they hatch and become larvae that are encysted in pig s muscle In U.S. transmission is mainly from human to human Humans can be intermediate host too!! Much more dangerous to be an intermediate host!

57 Helminths: Phylum Platyhelminthes: Class Cestodes Tapeworms Humans as Intermediate Hosts for Tapeworms Example: Echinococcus granulosus Dogs and coyotes are definitive hosts Usual intermediate hosts: sheep, deer but can be humans Causes a generalized invasion of the soft tissues of the body.

58 Figure Overview

59 Helminths Phylum NematodaNematodes: Roundworms 1. Characteristics Cylindrical and tapered at each end Have a complete digestive system mouth, intestine, and anus Most are dioecious Males are smaller than females and have one or two hardened spicules on their posterior ends (used to guide sperm to the female s genital pore).

60 Enterobius vermicularis, the pinworm Figure Overview

61 Helminths: Nematodes (phylum Nematoda) Roundworms 2. Infections : 2 Categories First category: Eggs infective for humans Example: Enterobius vermicularis (pinworm)» Entire life spent in humans. Found in large intestine. Scotch tape prep (Graham sticky tape method) used in diagnosis. See eggs stuck to tape Example: Ascaris lumbricoides» Adult lives in humans and domestic animals. Transmitted by eggs being eaten. Can make lab diagnosis with eggs or adult worms.

62 Figure 25.25: Ascaris lumbricoides, the cause of ascariasis.

63 Helminths: Nematodes (phylum Nematoda) Roundworms 2. Infections 2 Categories Second category: Larvae infective for humans Example: Necator americanus (Hookworm)» Hookworms found in small intestine of humans. Diagnosis is made on basis of eggs in feces. See hooked shaped adult and cutting plates in mouth used for attachment in gut. Example: Trichinella spiralis» Come from eating encysted larvae in undercooked pork. Diagnosis is made by larvae in muscle biopsy.

64 Figure Overview (1 of 4)

65 Figure 25.26: The life cycle of Trichinella spiralis - Overview. Trichinella spiralis adults develop, invade intestinal wall of pig, and produce larvae that invade muscles. Capsule Garbage, including undercooked or raw pork Section showing T. spiralis larvae encysted in pig s muscle tissue. Meanwhile, other animals are infected by eating infected meat that has been dumped. Undercooked pork Human eats undercooked pork containing cysts. 0.5 mm Section of T. spiralis. (a) In human intestine, cyst walls are removed, and T. spiralis adults develop. Adults produce larvae that encyst in muscles. Life cycle of Trichinella spiralis, the causative agent of trichinellosis (b) T. spiralis adult 0.1 mm

66 Arthropods as Vectors Arthropods are the largest phylum in animal kingdom Some inadvertently act as a mechanical vector for disease transmission Example: houseflies transfer enteric pathogens Others diseases require a biological vector for transmission Example: mosquitoes transfer malaria(plasmodium) after a mandatory development life cycle in the mosquito Control strategies of vector borne diseases usually focus on eliminating the vector Example: mosquitoes abatement programs

67 Mosquitoes are a biologic vector for malaria Figure Overiview

68 The tick, Ixodes pacificus is a biologic vector of Lyme Disease on the Pacific Coast Figure 12.32

69 Other examples of arthropod biological vectors Figure Overview