Lecture 5: Survey of the microbial world
Edith Porter, M.D.
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 Classification of microorganisms
▪ Taxonomy
▪ Three domain system: Bacteria, Archaea, Eukarya
 Prokaryotes
▪ Bacteria
▪ Archaea
 Eukaryotes
▪ Protozoa
▪ Algae
▪ Fungi
▪ Helminths
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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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The study of the evolutionary history of
organisms
All Species Inventory (2001–2025)
 To identify all species of life on Earth
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Species definition
 Eukaryotes: breed among themselves
 Prokaryotes: > 97% homology in 16S rRNA
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Cladograms used to establish relation ship
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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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Obligate intracellular bacteria
Cannot proliferate outside of a host cell
Selected human pathogens
 Rickettsia
 Chlamydia
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Transmitted by ticks or lice
Infects vascular endothelial cells
R. rickettsii: Rocky Mountain spotted fever
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Eukaryotic
Aerobic or facultatively anaerobic
Chemoheterotrophic
Most are decomposers
Asexual and sexual spore formation
 For Reproduction, not endurance!!
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Broad use of fungi
 Food, food production, drugs
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Mycology is the study of fungi
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, absorptive
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YEASTS
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Unicellular
Proliferate by budding or
fission
Candida albicans
MOLDS
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Multicellular
Septated and unseptated
hyphae
Mass of hyphae is mycelium
Aspergillus spec., Rhizopus
spec.
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Switch growth phase depending on environmental
conditions
 Pathogenic dimorphic fungi are yeastlike at 37°C and
moldlike at 25°C
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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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Yeasts
 Candida: Candidiasis
 Cryptococcus: Meningitis
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Molds
 Aspergillus: Lung infection in neutropenic patients
 Rhizopus, Mucor: in diabetes patients
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Dimorphic
 Coccidioides: Lung infections
 Histoplasma: Lung infections
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Dermatophytes
 Trichophyton, Epidermophyton: Tinea
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Eukaryotic
Always unicellular
Chemoheterotrophs
Digestion in vacuoles
Often complex life cycles with multiple hosts and
vectors
 Some produce cysts
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 Resistant survival forms
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Vegetative form is a trophozoite
Reproduction
 Asexual
 Sexual reproduction
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Archaezoa: Trichomonas, Giardia
Amaebazoa: Entamoeba
Apicomplexa: Plasmodium
Ciliophora: Balantidum
Euglenozoa: Trypanosoma
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Eukaryotic
Multicellular, organ differentiation
Kingdom: Animalia
 Phylum: Platyhelminthes (flatworms)
▪ Class: Trematodes (flukes)
▪ Class: Cestodes (tapeworms)
 Phylum: Nematodes (roundworms)
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Chemoheterotrophic
Multiple hosts
 Intermediate host
 Definitive host: adult form develops, sexual reproduction
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Monoecious (hermaphroditic)
 Male and female reproductive systems in one
animal
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Dioecious
 Separate male and female
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Egg  larva(e)  adult
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Oral sucker: food uptake
 Incomplete digestive tract
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Ventral Sucker: Attachment
Mostly hermaphroditic (monoecious)
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Sucker for
attachment
No digestive tract
 Food uptake by
absorption
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Hermaphrodites
(monoecious)
Scolex, neck,
proglottides
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Necator americanus
(hook worm)
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Dioecious (male, female)
Complete digestive tract
Caenorrhabditis elegans: model system
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Fungi
 Molds (septated, unseptated), yeast, dimorphic
 Sexual and asexual spores
 Mycoses: local or systemic impairment of host
defense
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Protozoa: always unicellular, often vectors
Helminths: always multicellular, complex life
cycles
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Eukaryotic
Multicellular, organ differentiation
Kingdom: Animalia
 Phylum: Platyhelminthes (flatworms)
▪ Class: Trematodes (flukes)
▪ Class: Cestodes (tapeworms)
 Phylum: Nematodes (roundworms)
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Chemoheterotrophic
Multiple hosts
 Intermediate host
 Definitive host: adult form develops, sexual reproduction
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