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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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Classification of microorgansims

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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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Cladogram to Establish the Evolutionary Relationship of Microorganisms

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Three domain system (Carl Woese)

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Model of the origin of eukaryots

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Major differences between domains (1)

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Major differences between domains (2)

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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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Prokaryotes

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The Prokaryotes

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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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Chlamydia (1)

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Chlamydia (2)

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Eukaryotes

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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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Comparison of fungi and bacteria

, absorptive

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Yeast and moldsYEASTS 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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Life cycle of Plasmodium vivax

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Helminths

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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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Life Cycle of Paragonimus westermani (Lung fluke)

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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