2 Intro to the Bacteria, Microscopy & Staining Flashcards
Diff b/w eukaryotes and prokaryotes?
Eukaryote: Cells contain membrane-bound organelles
Prokaryote: Cells lack internal membrane-bound nucleus and other organelles
Name 5 microorganisms, and indicate whether they’re prokaryotic, eukaryotic, or neither.
- Bacteria (prokaryotic)
- Fungi (eukaryotic)
- Algae (eukaryotic)
- Parasites (eukaryotic)
- Viruses (neither)
Name the 3 Domains/Kingdoms of life.
- Eukarya (eukaryotic)
- Bacteria (prokaryotic)
- Archaea (prokaryotic)
Name two characteristics of archaea.
- Inhabit extreme envirs
2. Don’t cause human diseases
Earliest lifeforms on the Earth?
Bacteria
How are bacteria named?
They have binomial nomenclature:
- Genus
- Species
How do we name bacteria that have identical genus and species but are slightly different from each other?
By adding a “strain” name to their binomial name.
T or F: Bacteria are usually only referred to by their genus, species, and strain. Rarely do we consider their other taxonomic categories (e.g. their phylum, class, order, etc.)
T
What’s the value of bacterial taxonomy? (3)
- Consistency of communication
- Assess relatedness of diff bacteria
- For medical practice
T or F: All strains of E. Coli cause the same disease
F
Diff strains of a bacteria can cause completely diff diseases.
Up to what magnification can light microscopy reach?
1000x magnification
T or F: Light microscopy is sufficient for most routine bacterial observations.
T
Up to what magnification can electron microscopy reach?
200,000x
Main drawback of electron microscopes?
Expensive, thus limited use
2 advantages and 1 disadvantage of staining for light microscopy?
Advantage: Increase contrast of specimen
Advantage: Preserve specimen for future observation
Disadvantage: Staining kills microbe
What method can be used so that the microbe ISN’T killed in the process of preparing it for observation via light microscopy?
Hanging Drop method (aka “wet mount”)
Disadvantage of wet mount?
Poor contrast
Advantage of wet mount?
Observe microbe movement.
Term for a coloured dye that binds to bacterial cells?
Stain
What’re the three steps involved in staining bacteria?
- Smear layer of bacteria on glass slide
- Fix the smear by air drying + mild heating
- Flood fixed smear w/ dye and wash unbound dye away
What step of staining kills the bacteria?
Air drying + heating the smeared slide
What’re the 3 types of stains?
- Simple stain
- Differential stain
- Special stain
Describe the simple stain.
a. A single dye is used
b. All bacteria appear as same colour
c. Cannot tell if diff species are present
Name two types of differential stains.
- the Gram Stain
2. the Acid-Fast Stain
Describe the steps of the Gram Stain (only the steps after heat-fixing the bacteria) (4)
- Flood heat-fixed smear w/ purple stain (all cells = purple)
- Add iodine (iodine allows stain to bind better; all cells are still purple)
- Decolourize cells w/ alcohol (Gram neg. cells become colourless)
- Counterstain w/ red dye (Gram neg. cells become red)
What colour is a Gram positive cell?
Purple
What colour is a Gram negative cell?
Red
T or F: Most bacterial species are “acid-fast”
F
Most are, in fact, NOT acid-fast
What’s the main difference b/w the acid-fast stain and the Gram stain?
The de-colourizing step - acid-fast stains use a harsher de-colourizing step (it uses acid-alcohol instead of alcohol)
Give an example of a bacteria that is acid-fast.
Mycobacterium tuberculosis
T or F: The dye of acid-fast bacteria are decolourized during the decolourizing step of acid-fast stains
F
Acid-fast bacteria are cannot be decolourized, and so remain the same colour (red) throughout the procedure
What are special stains used for?
To see structures that’re not normally seen using light microscopy
Give two structures that can observed using special stains.
- Spores
2. Flagella
What is a “pure culture”?
A pop of bacteria consisting of only ONE species or strain.
All bacteria are genetically identical to one another.
What method is used to get a pure culture of bacteria?
the “streak plate” method
How can diff bacterial species be distinguished on an agar surface?
By “colony morphology”
