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MICR 201 Microbiology for Health Related Sciences
Lecture 5: Survey of the microbial worldEdith Porter, M.D.
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Lecture Outline
Classification of microorganisms▪ Taxonomy▪ Three domain system: Bacteria, Archaea,
Eukarya Prokaryotes▪ Bacteria▪ Archaea
Eukaryotes▪ Protozoa▪ Algae▪ Fungi▪ Helminths
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Taxonomy
The science of classifying organisms Provides universal names for
organisms Provides a reference for identifying
organisms Initially based on morphology and
biochemical assays Now based on nucleic acid
sequencing (16S and 18S rRNA analysis)
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Phylogeny (or systematics)
The study of the evolutionary history of organisms
All Species Inventory (2001–2025) To identify all species of life on Earth
Species definition Eukaryotes: breed among themselves Prokaryotes: > 97% homology in 16S
rRNA Cladograms used to establish
relation ship
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Important to Remember
Taxonomy is the science of classification using a hierarchical system
Universal ancestor The three domains differ in presence of
a nucleus (eukarya), ether linked lipids (archaea) and use of formylmethionine as started amino acid in protein synthesis (bacteria)
Cladograms are used to establish evolutionary relationships
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Selected bacterial life forms
Obligate intracellular bacteria Cannot proliferate outside of a host
cell Selected human pathogens
Rickettsia Chlamydia
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Rickettsia Transmitted by ticks or lice Infects vascular endothelial cells R. rickettsii: Rocky Mountain spotted
fever
http://www.lincolner.com/Lincoln%20page%203/images/rocky%20mountain%20spotted%20fever1.jpg
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Fungi
Eukaryotic Aerobic or facultatively anaerobic Chemoheterotrophic Most are decomposers Asexual and sexual spore formation
For Reproduction, not endurance!! Broad use of fungi
Food, food production, drugs Mycology is the study of fungi
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Yeast and molds
YEASTS Unicellular Proliferate by budding
or fission Candida albicans
MOLDS Multicellular Septated and unseptated
hyphae Mass of hyphae is
mycelium Aspergillus spec.,
Rhizopus spec.
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Dimorphic fungi
Switch growth phase depending on environmental conditions
Pathogenic dimorphic fungi are yeastlike at 37°C and moldlike at 25°C
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Fungal diseases
Systemic mycoses: Deep within body
Subcutaneous mycoses: Beneath the skin
Cutaneous mycoses: Affect hair, skin, and nails
Superficial mycoses: Localized, e.g., hair shafts
Opportunistic mycoses: Caused by normal microbiota or environmental fungi
Note: antibiotics do not work against fungi!
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Medically relevant fungi
Yeasts Candida: Candidiasis Cryptococcus: Meningitis
Molds Aspergillus: Lung infection in neutropenic patients Rhizopus, Mucor: in diabetes patients
Dimorphic Coccidioides: Lung infections Histoplasma: Lung infections
Dermatophytes Trichophyton, Epidermophyton: Tinea
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Protozoa Eukaryotic Always unicellular Chemoheterotrophs Digestion in vacuoles Often complex life cycles with multiple
hosts and vectors Some produce cysts
Resistant survival forms Vegetative form is a trophozoite Reproduction
Asexual Sexual reproduction
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Medically Important Phyla of Protozoa
Archaezoa: Trichomonas, Giardia Amaebazoa: Entamoeba Apicomplexa: Plasmodium Ciliophora: Balantidum Euglenozoa: Trypanosoma
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Characteristics of Helminths Eukaryotic Multicellular, organ differentiation Kingdom: Animalia
Phylum: Platyhelminthes (flatworms)▪ Class: Trematodes (flukes)▪ Class: Cestodes (tapeworms)
Phylum: Nematodes (roundworms) Chemoheterotrophic Multiple hosts
Intermediate host Definitive host: adult form develops, sexual
reproduction
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Life Cycle of Helminths
Monoecious (hermaphroditic) Male and female reproductive systems in
one animalDioecious
Separate male and femaleEgg larva(e) adult
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Trematodes (Flukes)
Oral sucker: food uptake Incomplete digestive tract
Ventral Sucker: Attachment Mostly hermaphroditic (monoecious)
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Cestodes(Tape Worms)
Sucker for attachment
No digestive tract Food uptake by
absorption Hermaphrodites
(monoecious) Scolex, neck,
proglottides
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NematodesRoundworms
Dioecious (male, female) Complete digestive tract Caenorrhabditis elegans: model system
Necator americanus (hook worm)
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Important to Remember
Fungi Molds (septated, unseptated), yeast,
dimorphic Sexual and asexual spores Mycoses: local or systemic impairment
of host defense Protozoa: always unicellular, often
vectors Helminths: always multicellular,
complex life cycles
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Helminths
Eukaryotic Multicellular, organ differentiation Kingdom: Animalia
Phylum: Platyhelminthes (flatworms)▪ Class: Trematodes (flukes)▪ Class: Cestodes (tapeworms)
Phylum: Nematodes (roundworms) Chemoheterotrophic Multiple hosts
Intermediate host Definitive host: adult form develops, sexual reproduction