Introduction & Classification of Human Microbiota Flashcards
According to the current system ‘The Tree of Life’, what 3 domains can all the living organisms on the planet be placed into?
- Bacteria 2. Archaea 3. Eukarya (eukaryotes)
Why are ‘viruses’ and ‘prions’ not included in the ‘Tree of Life’?
These “infectious particles” do not satisfy the criteria for a living organism
What is taxonomy?
The science of naming, describing and classifying organisms and includes all plants, animals and microorganisms of the world
What are the 8 levels of taxonomy?
The taxonomic hierarchy has eight ranks from general to specific: 1. Domain 2. Kingdom 3. Phylum 4. Class 5. Order 6. Family 7. Genus 8. Species
What is a ‘domain’? What are the 3 ‘domains’?
A domain is the highest (most general) rank of organisms. There are 3 domains of life: 1. Bacteria 2. Archaea 3. Eukaryota
Regarding ‘Escherichia coli’ as an example, what does each part of the name denote?
‘Escherichia’ - genus ‘Coli’ - species
How is it decided where bacterial species are placed in the tree of life? How is this used?
Focus on the DNA 16S rRNA sequence –> you can classify bacteria into groups depending on how similar this piece of DNA is I.e. bacteria that are closely related will have a very similar 16S
Why is the 16s rRNA sequence used?
A piece of DNA that is present in all bacteria and is highly conserved
What are bacteria? Do they have a membrane bound nucleus?
Simple, single cell organisms They lack a membrane bound nueclues
Prokaryote vs eukaryote?
Prokaryotes are organisms made up of cells that lack a cell nucleus or any membrane-encased organelles. Eukaryotes are organisms made up of cells that possess a membrane-bound nucleus that holds genetic material as well as membrane-bound organelles
Are bacteria pro or eukaryotes? Why?
Prokaryotes as lack a membrane bound nucleus
Diagram of bacteria. What are the noticeable features?
- Nucleoid (including chromosomal DNA)
- Capsule (if present)
- Cell envelope
- Plasma membrane
- Polysomes
- Plasmid DNA
- Fimbriae
- Flagellum

What is the flagella? What is it responsible for?
- Long tail-like structure
- Responsible for locomotion (motility)
E.g. bladder infection –> ability of bacteria to move up the urethra
The number and location of flagella can vary. What are the different options?
- Monotrichous (A)
- Lophotrichous (B)
- Amphitrichous (C)
- Peritrichous (D)

What bacteria is the main cause of UTIs?
E. coli
What is the ‘H antigen’? What is this used for?
Flagella is the whole structure, while the slender threadlike portion of the flagella is called the H antigen.
Used for the identification of the certain pathogens
What are fimbriae? How do they differ from pili?
Both are structures exposed to the extracellular space (very similar)
Fimbriae:
- Bristle like short fibres occurs on the surface of bacteria
- Present on both Gram positive and Gram negative bacteria
Pili:
- Long hair like tubular microfibres like structures present on the surface of bacteria.
- Present only on some Gram negative bacteria.
What is the importance of fimbriae/pili to bacteria?
Aid adhesion to host cells and colonisation (helpful in ability to cause an infection)
What is the capsule of bacteria? Are they present in all bacteria?
It is a polysaccharide layer that lies outside the cell envelope, and is deemed part of the outer envelope of a bacterial cell.
Present in most but not all bacteria.
What is purpose of capsule of bacteria?
- Polysaccharide material protection from
- Phagocytosis/immune attack
- Dessication
- Antibiotics
Difference between a slime layer and a capsule?
Slime layer:
- Loosely associated with the bacterium
- Can be easily washed off
Capsule:
- Attached tightly to the bacterium
- Has definite boundaries
What are bacteria biofilms?
Community of bacteria surrounded by extracellular polymeric substances (layer) –> another example of polysaccharide protection
What is an endospore?
An endospore is a dormant, tough, and non-reproductive structure produced by certain bacteria.
What is purpose of endospores?
Resistant to many forms of environmental stress (allow bacteria to persist):
- Dessication
- UV radiation
- Temperature extremes
- Certain antiseptic agents












