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Chapter 12
Eukaryotic organisms of concern to microbiologists
FUNGI
ALGAE
PROTOZOA
HELMINTHS
ARTHROPODS
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Fungi
Mycology is the study of fungi
Fungal characteristics:
 eukaryotic
 Energy Source: chemoheterotrophs (saprophytic)
 O2 needs: aerobic, facultative anaerobic
Form: multicellular (molds), unicellular (yeasts)
dimorphic fungi have both forms
Cell wall contains chitin
Classified based on their form of sexual reproduction
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Fungal Vegetative Structures
Thallus: the body of the mold or fleshy fungus (mushrooms)
consists of long filaments called hyphae which are joined together
Hyphae in most molds are divided into individual cell units
by septa (cross walls)
Coenocytic hyphae do not have septa (aseptate)
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Yeasts
Reproduce by two different kinds of division
fission yeasts - undergo binary fission
budding yeasts - divide unevenly through buds
pseudohyphae are short chains formed when the buds do not
completely separate
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Fungal Divisions: Zygomycota
"conjugation" fungi (fig. 12.6, p. 337)
Zygospore - large spore
enclosed by a thick wall
sexual reproduction by zygospores
(union of two nuclei from mating strains of fungus)
asexual reproduction by sporangiospores in a sporangium
coenocytic hyphae (no septa/cross walls)
Example: Rhizopus (includes black bread mold)
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Fungal Divisions: Ascomycota
"sac" fungi (fig. 12.7, p. 338)
sexual reproduction by ascospores in a sac called an ascus
asexual reproduction by conidiospores on conidia
septate hyphae
Examples: Sachcharomyces - brewer’s yeast, Aspergillus, Histoplasma
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Fungal Divisions: Basidiomycota
"club" fungi (fig. 12.8, p. 339)
sexual reproduction by basidiospores on a pedestal called a basidium
asexual reproduction by fragmentation
septate hyphae
Examples: Coprinus, Amanita
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Fungal Divisions: Deuteromycota
"fungi imperfecti” - a ‘holding category’ for organisms in which
sexual reproduction is not discovered… may exist though.
Why ‘imperfect’? -- no known sexual reproduction
asexual reproduction by conidiospores
septate hyphae
Example: Candida albicans
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Fungal Diseases
a fungal infection is called a mycosis (plural = mycoses)
cutaneous mycoses: fungal infections of the hair, skin, and nails
subcutaneous mycoses: infections under the skin, often occur by
direct implantation of fungal spores or mycelium into a puncture of the
skin
systemic mycoses: deep in the body, can affect multiple
organs and tissues
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Fungal Disease ...
some fungi are opportunistic pathogens
Example: candidiasis (yeast infection, thrush) Candida albicans
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Algae
simple eukaryotes - unicellular, colonial, and multicellular
photoautotrophs
vegetative structures:
body of multicellular alga is called a thallus
some have holdfasts, stem-like stipes, and leaf-like blades
live in water habitats
divisions determined by a number of characteristics, including:
pigments, cell wall types, and food storage polymers
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Some Algae Divisions
Brown algae:
macroscopic (some up to 50 m long)
producers of algin (used as commercial food thickener such as in ice
cream, sour cream, yogurt)
Red algae:
delicately branched, live at great depth
source of agar
Green algae:
cellulose cell walls, chlorophyll a and b
believed to be precursor to terrestrial plants
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More Algae Divisions
Diatoms - silica in cell wall
can produce domoic acid - a toxin concentrated by shellfish
Dinoflagellates:
unicellular algae, known as plankton
produce neurotoxins
Gonyaulax, dinoflagellate found in red tides, produce saxitoxins
that cause paralytic shellfish poisoning
Euglenoids:
unicellular, flagellated algae
have rigid cell membrane (pellicle), but no cell wall
contain a red eyespot
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Lichens – a partnership
A lichen is a combination of a green alga (or cyanobacterium) and a
fungus
they live together in a mutualistic relationship (both benefit) & occupy
habitats where neither would survive alone
fungus provides holdfast and protection
algae provides nutrients through photosynthesis
chemical weathering of rocks by lichens contributes to soil formation
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Slime Molds
have characteristics of both fungi and animals (classified as protists)
complex life cycle (see figs. 12.21 & 12.22, p. 356-7)
slime molds resemble giant amoebas
life singly, or in aggregates called a plasmodium
representative genus: Dictyostelium
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Protozoa
have both asexual and sexual reproduction
some produce cysts for survival in adverse conditions
classified by their mode of motility:
Sarcodina - amoebas
Mastigophora - flagellates
Ciliophora – ciliates
Apicomplexa - nonmotile
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Medically-important Protozoa
Sarcodina:
Entamoeba histolytica, amoebic dysentery
Naegleria fowleri, meningocephalitis
Mastigophora
Giardia lamblia, giardial enteritis
Trichomonas vaginalis, vaginitis
Trypanosoma cruzi (Chaga’s disease)
T. brucei (African trypanosomiasis)
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Medically-important Protozoa
Ciliophora
Balantidium coli, dysentery (only parasitic ciliate of humans)
Apicomplexa
Plasmodium, malaria (through bite of Anopheles mosquito)
Toxoplasma gondii, toxoplasmosis
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Helminths
Flatworms & Roundworms
multicellular, eukaryotes generally possess digestive, circulatory,
nervous, excretory, and reproductive systems
when parasitic may:
 lack digestive system
 have reduced nervous system
 have reduced locomotion
but no reduction in reproductive system
can have complex lifecycle with successive intermediate hosts for
larval stages and a definitive host for the adult parasite
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Reproductively may be:
monoecious: male and female reproductive organs in one organism
dioecious: male and female reproductive organs on separate individuals
Platyhelminths
flatworms
Two major groups
Trematodes - flukes
Cestodes - tapeworms
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Trematodes (flukes)
flat, leaf-shaped bodies with ventral and oral sucker (fig. 12.22)
can also absorb food through their outer layer (cuticle)
common names from tissue of definitive host in which they reside
(liver fluke, lung fluke, etc.)
Paragonimus life cycle (fig. 12.24)
Schistosoma – blood fluke are not ingested, but burrow through skin
Clonorchis – Asian liver fluke (no intermediate hosts in USA)
sometimes seen in immigrants, not transmitted
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Cestodes (tapeworms)
Scolex – ‘head’ of suckers & hooks attaches to intestinal mucosa see photo on
12.25 p 360
body consists of segments called proglottids: each segment contains
a complete, monoecious reproductive system (male & female)
Taenia saginata (beef tapeworm) - humans are definitive host
cattle are intermediate host
Proglottids wiggle away from feces increasing their chances
of being eaten by cattle in surrounding grass.
eggs hatch, larvae migrate to muscle, encyst as cysticerci in muscle
which is eaten by humans
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Attach to intestinal wall by scolex, grow & reproduce
Other tapeworms
Echinococcus granulosus – dog tapeworm
Taenia solium – pork tapeworm
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Nematodes (roundworms)
Most species are dioecious
some infect humans as eggs: Enterobius – pinworm, female migrates
to anus to lay eggs (diagnosis by tape method)
acquired by exposure to contaminated bedding
Ascaris lumbricoides which exhibits sexual dimorphism – eggs in
soil, accidental ingestion
some infect humans as larvae (hookworm, Necator americanus
which enters through skin -- prevented by wearing shoes;
Trichinella spiralis, cause of trichinosis, acquired by eating larvae
in poorly cooked pork)
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Arthropods as vectors
Arthropods (joint footed) are the largest phylum in the animal kingdom
Includes: Insects, Arachnids, Crustaceans
can act as vectors (transmitters) of many pathogenic microorganisms
Mites and ticks: some carry Rocky Mountain spotted fever,
Lyme disease, relapsing fever
Sucking lice: epidemic typhus
Fleas: endemic murine typhus, plague
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Arthropods as vectors…
Flies (includes mosquitoes): Tularemia, Dengue fever, yellow fever,
malaria, arboviral encephalitis, African trypanosomiasis
True bugs: Chaga’s disease (kissing bug)
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