Chapter 12: Fungi, Algae, Protozoa,
and Multicellular Parasites
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.
Table 12.1
Table 12.2
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
Figure 12.1 - Overview
Figure 12.2 - Overview
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)
Figure 12.3
Figure 21.17: Candidiasis - Overview.
Chlamydoconidia
Pseudohyphae
Blastoconidia
(a) Candida albicans
(b) Oral candidiasis, or thrush
20 mm
Fungi: Vegetative Structures
– 3. Dimorphic Fungi
• Some fungi, especially pathogenic fungi, exhibit
two forms of growth – yeastlike at 370C and
moldlike at 250C
• Examples of human pathogens that are
dimorphic
– Histoplasma capsulatum
– Coccidioides immitis, Valley Fever
Figure 12.4
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.
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.
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)
Figure 12.5a
Figure 12.5b
Figure 12.5c
Figure 12.5d
Figure 12.5e
Fungi: Nutritional Adaptations
– Differ from bacteria in the following ways:
• 1. Grow best at pH 5.0
• 2. 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
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
Figure 12.6 - Overview
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)
Figure 12.7 - Overview
Figure 12.9 - Overview
Figure 12.8 - Overview
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
Fungi: Economic Effect of Fungi
– Undesirable effects
• 1. Spoilage of food. Grow where bacteria cannot.
– Fruit, grains, vegetables, jams/jellies
• 2. Plant pathogens
– Dutch elm disease carried by bark beetles devastated US
tree population
– Chestnut blight imported from China (1904) killed
nearly all chestnut trees in US
– Benefits
• 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.
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.
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.
Figure 12.17b
Figure 12.17c
Figure 12.17d
Figure 12.17a
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
Figure 12.18 - Overview
Acanthamoeba in corneal scraping
Cornea clouding due to Acanthamoeba
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.
Figure 12.19 - Overview
Unstained oocysts of Toxoplasma in stool
Cerebral T. gondii encephalitis in a patient with AIDS
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
Figure 12.20 - Overview
Figure 12.16
Figure 23.22: Trypanosoma cruzi, the cause of Chagas' disease (American trypanosomiasis).
2.5 µm
Naegleria trohpozoites in experimentally infected mouse brain
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)
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
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.
Clonorchis senensis life cycle
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
Paragonimus westermani (lung fluke) life cycle
Figure 12.26 - Overview
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.
General anatomy of an adult
cestode (tape worm)
Figure 12.27 - Overview (1 of 3)
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
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!
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.
Figure 12.28 - Overview
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).
Enterobius vermicularis, the pinworm
Figure 12.29 - Overview
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.
Figure 25.25: Ascaris lumbricoides, the cause of ascariasis.
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.
Figure 12.30 - Overview (1 of 4)
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.
Section of
T. spiralis.
Meanwhile, other
animals are
infected by eating
infected meat
that has been
dumped.
0.5 mm
Undercooked pork
Human eats
undercooked
pork containing
cysts.
In human intestine,
cyst walls are removed,
and T. spiralis adults
develop. Adults produce
larvae that encyst in
muscles.
(a) Life cycle of Trichinella spiralis, the causative agent of trichinellosis
(b) T. spiralis adult
0.1 mm
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
Mosquitoes are a biologic vector for malaria
Figure 12.31 - Overiview
The tick, Ixodes pacificus is a biologic vector of Lyme Disease on the Pacific Coast
Figure 12.32
Other examples of arthropod biological vectors
Figure 12.33 - Overview