Fungi, Protozoa, and Helminths

• The slides summarise key facts about Fungi, Protozoa and Helminths

Fungi

• Fungi are eukaryotic
• Fungi are non-motile
• Fungi have cell walls composed of chitin
• Fungi are absorptive heterotrophs
• They secrete exoenzymes into the environment
• They absorb digested nutrients

Fungi - Saprophytes and Parasites

• Most fungi are saprophytes and decompose dead organic matter
• Some fungi are parasites of plants, animals, and humans

Types of Fungi

• Yeasts (Figure 12.2) are unicellular
• Molds (Figure 12.3) are multicellular, filamentous
• Macrofungi (Figure 12.4) are multicellular, filamentous and produce fleshy reproductive structures like mushrooms, puffballs, and shelf fungi

Fungi Morphology

• Hypha(e) are filaments of fungal cells
• Mycelium is a mass of fungal filaments (hyphae)
• Hyphae may be septate or nonseptate

Thermally Dimorphic Fungi

• Thermally dimorphic Fungi switch between unicellular or mycelial growth depending on temperature.
• Yeast form is invasive due to the production of enzymes and proteins that allow survival within the body

Fungi Reproduction

• Fungal sexual cycles are complex and involve both sexual and asexual forms (12-10)
• Gametangia are specialized cells (structure) producing gametes (12.13)
• Sporangia are specialized cells (structure) producing spores (12.11).
• Typically, the only diploid cell in the cycle is the zygote
• Typically, the zygote immediately undergoes meiosis to produce haploid spores

Candida albicans

• Candida albicans is a yeast
• It is normal flora of the respiratory, gastrointestinal, and female urogenital tract (12.18)
• It reproduces asexually by budding, potentially resulting in pseudohyphae (p.788)
• May cause opportunistic diseases like thrush of the oral cavity and vulvovaginitis
• Systemic candidiasis may occur in immunocompromised patients with lung infection, endocarditis, etc

Saccharomyces cerevisiae

• Saccharomyces cerevisiae is Brewer's yeast and is used in the production of bread, wine, and beer (12.16, 12.17)
• It is non-pathogenic
• It does not form mycelium, but forms colonies similar to bacteria (12-7)

Rhizopus

• Rhizopus stolonifer is common bread mold, appearing as white or grayish, cottony growth (12.5)
• It shows a salt and pepper appearance due to the production of sporangia
• Branch filaments from hypha of different mating types form gametangia (n)
• Gametangia fuse to generate zygote (2n)
• Zygote undergoes meiosis to form sporangium (n)
• Sporangium releases haploid spores

Aspergillus

• Aspergillus has a distinctive fruiting body and variety of colors (12.19, 12.20)
• A. niger produces black colonies
• Conidia, asexual spores, are formed at the end of hypha

Aspergillus - Opportunistic Pathogen

• Some Aspergillus species are opportunistic pathogens, for example A. fumigatus
• Aspergillosis is actually many diseases
• Pulmonary aspergillosis is a fungus ball and involves growth in tissue damaged by tuberculosis
• Allergic aspergillosis may occur in individuals who are in infrequent contact with spores and become sensitized, with symptoms similar to asthma
• Invasive aspergillosis is the most severe form and may spread from the lungs (necrotizing pneumonia) to other organs

Penicillium

• Penicillium exhibits green, powdery, radially furrowed colonies with a white apron (12-22)
• Penicillium is a source of penicillin
• Penicillium is a common contaminant (bread mold, etc)
• Penicillium are thermally dimorphic

Penicillium - Opportunistic Pathogen and Food Production

• One Penicillium species (sp=singular) is an opportunistic pathogen in immunosuppressed individuals (thermally dimorphic)
• Other species (spp=plural) are important in cheese manufacture, for example, blue cheese

Laboratory Observations - Plate Cultures

• Penicillium sp. is grown on potato dextrose agar at 25 degrees C
• Rhizopus sp. is grown on potato dextrose agar at 25 degrees C
• Saccharomyces cerevisiae is grown on Sabouraud media at 30 degrees C
• Prepare a wet mount of S. cerevisiae and stain with methylene blue

Laboratory observations - Prepared slides

• Prepared slides for Candida albicans
• Prepared slides for Penicillium spp: Observe and identify conidiophores
• Prepared slides for Rhizopus spp: Observe and identify sporangia

Protozoans

• Protozoans include Euglena, Paramecium, Stentor, Amoeba and Balantidium coli (troph)

Protozoans of Clinical Importance

• Protozoans are unicellular, heterotrophic microorganisms
• Their typical lifestyle involves a Trophozoite which is a vegetative, active stage (12-27, 12-35) and a Cyst which is a resting stage that provides protection outside of hosts (12-28, 12-30)
• The Definitive host is the host where sexual reproduction occurs
• The Intermediate host is the host where asexual reproduction occurs

Entamoeba histolytica - Amoebic dysentery

• Entamoeba histolytica causes amoebic dysentery (amoebiasis) (12-27)
• Transmission occurs through the fecal-oral route, as cysts resist stomach acids
• Excystation occurs in the small intestine, and trophozoites parasitize the mucosa of the colon
• Symptoms include blood and mucus in diarrhea (dysentery), and vomiting
• Cysts can be found in a stool sample (12-28)
• The disease may be mild or severe
• A carrier may be asymptomatic but still be a major source of infection
• Infection may spread to other organs

Giardia Lamblia - Beaver Fever

• Giardia Lamblia is a flagellate protozoan that causes giardiasis also known as Beaver Fever
• The trophozoite is in the duodenum (12-33)
• Cysts are shed in feces (12-34)
• Transmission occurs via the fecal-oral route
• Most infections are asymptomatic
• May cause chronic diarrhea and abdominal pain

Trichomonas vaginalis - Vulvovaginitis

• Trichomonas vaginalis has four anterior flagella and an undulating membrane (12-35)
• It causes Trichomoniasis, also known as vulvovaginitis
• It may affect both sexes, but is more common in women
• Most infections are asymptomatic or mild
• May be discharge or tissue erosion
• Transmission occurs through sexual intercourse

Trypanosoma brucei

• Trypanosoma brucei is a flagellated protozoan (12-36)
• Its life cycle involves humans and the tsetse fly
• Trypanosoma brucei causes Sleeping sickness
• Sleeping sickness is caused by multiple subspecies with varying rates of disease progression
• The central nervous system is affected, leading to sleepiness and emaciation
• Sleeping sickness has a high mortality rate

Plasmodium spp. - Malaria

• Plasmodium spp. are sporozoan parasites with a complex lifestyle (12-37) and cause malaria
• The Anopheles mosquito is the definitive host for the sexual phase
• Sporozoites are injected into humans through mosquito saliva
• Humans are the intermediate host for the asexual phase
• Sporozoites travel to and reproduce in the liver, and merozoites travel to RBCs and reproduce as trophozoites (12-38, 12-39, 12-40)
• Spiking fever occurs when parasites rupture RBCs
• The parasite is ingested by a mosquito, where sexual reproduction occurs and the life cycle continues

Toxoplasma gondii

• Toxoplasma gondii is a sporozoan (12-41) that infects cat intestines
• Cysts are shed in cat feces
• In humans, the disease is generally mild, including fatigue and muscle aches
• The fetus may be infected from an infected mother, potentially resulting in stillbirth

Parasitic Helminths Overview

• Parasitic Helminths Overview includes Platyhelminthes (Flatworms) and Nematodes (Roundworms)

Platyhelminthes - Flatworms

• Platyhelminthes are flatworms. This group includes Trematodes (Flukes) and Cestodes (Tapeworms)
• Trematodes include Liver flukes and Lung flukes
• Cestodes include Beef tapeworm and Pork tapeworm
• Nematodes are roundworms. This group includes Ascaris lumbricoides, Pinworms, and Hookworms

Platyhelminthes- Trematodes

• Liver fluke (Clonorchis (Opishtorchis) sinensis) (12-42) is transmitted through infection due to consumption of undercooked fish
• Liver flukes lay eggs in the liver bile ducts, and the eggs are released in feces (12-43)
• Lung fluke (Paragoniimus westermani) (12-44) is transmitted via undercooked crabs or crayfish infected with cysts is ingested by humans
• Juveniles travel to the lungs and mature
• Eggs are released in sputum, lung fluids or feces (12-45)

Platyhelminthes- Cestodes - Scolex and Proglottids

• Cestodes (Tapeworms) contain a scolex (12-48, 12-51, 12-54, 12-59)
• Cestodes (Tapeworms) contain proglottids (12-49, 12-51, 12-55, 12-58, 12-60)
• The Tapeworm, Taenia spp. contains the beef tapeworm (T. saginata) (12-57,12-58) which is transmitted when humans eat undercooked beef containing juvenile worms
• Taenia spp,. also contains the pork tapeworm (T. solium)(12-59, 12-60) is transmitted when humans eat undercooked pork containing juvenile worms

Nematodes - Ascaris lumbricoides

• Ascaris lumbricoides is a large nematode is up 49cm long in females (12-61,12-62)
• Ascaris lumbricoides infects when eggs are ingested (12-63, 12-64)
• Juveniles travel from the intestine to the lungs, up the esophagus, and then back to the intestine
• Infection may result in Ascaris pneumonia

Nematodes - Pinworms

• Pinworms is also known as Enterobius vermicularis (12-65)
• Transmission occurs via the fecal-oral route
• This is common in children due to poor sanitary habits
• Eggs are rarely found in feces, as they are laid by the female in the perianal region (12-66)

Nematodes - Hookworms

• Hookworms (Ancylostoma duodenale, Necator americanus) occurs when juveniles penetrate the skin, enter the blood, and travel to the lungs (12-67, 12-68)
• They are carried up and out of the lungs by the ciliary escalator
• When reaching the pharynx, they are swallowed
• In the small intestines, they attach and mature into adults
• They feed on blood and tissue
• Eggs are passed in feces (12-69)

Laboratory observations (Prepared slides)

• The following protozoa are observed: Trichomonas vaginalis trophozoite 93-10, Trypanosoma spp. 93-12, Plasmodium spp. (ring stage or blood smear) 93-09
• The following helminthes are observed: Ancylostoma duodenale or 96-17, Enterobius vermicularis adult (pinworm), eggs 96-18, Necator americanus adult 96-18, Taenia (Tapeworm) – scolex and proglottids

Laboratory observations (Whole preserved specimens)

• The following nematodes are observed: Ascaris lumbricoides (in small thin bottle + 2 Biomounts), Ascaris – plexiglass whole mounts
• The following platyhelminthes are observed: Taenia sp. (small and medium size jars), Biomount Whole Mount of Types of Flatworms