Bacteriology Introduction

Question 1

Describe the 3 domains of life

Answer 1

1. Bacteria (prokaryotes)
2. Archaea (prokaryotes)
   
   • Archaea are closer to eukaryotes
   • They live in weird environmnets and do not infect humans
3. Eukaryotes

Question 2

How do bacteria reproduce?

Describe the 4 phases of growth and the growth curve

What does the growth curve allow us to do?

Answer 2

• Via binary fission (1 fission produces 2 identical daughters)
  
  • 4 phases of growth
  1. Lag phase: bacteria readjust to the new environment
  2. Log phase: growth surges
  3. Stationary phase: nutrients run out, start to produce toxic and products, and stop growing
  4. Death phase: die off
• These curves allow us to calculate the generation time: the time it takes for doubling of the population

Question 3

Bacterial classification: describe the 5 ways bacteria are classified based on their O₂ utilisation (metabolism) (define obligate aerobe, anaerobe; facultative anaerobe; areotolerant anaerobe; microaerophile)

Answer 3

1. Obligate aerobe: require oxygen for growth
   
   • Ex., humans
2. Obligate anaerobe: oxygen is toxic for growth
3. Facultative anaerobe: use oxygen if present (due to the better energy yield), but can also grow with or without oxygen
4. Aerotolerant anaerobes: don’t use oxygen but it is not toxic to them
5. Microaerophile: grow best with low levels of oxygen

Question 4

Bacterial classification: describe how bacteria are classified by taxonomic ranks (4 levels)

Answer 4

1. Domain: Bacteria
2. Genus: Escherichia
3. Species: coli
4. Strain: O157:H7
   
   • O identifies the specific O-antigen of the strain

Question 5

Describe the gram staining process

Answer 5

1. Dye cells violet
2. Add iodine to fix the dye
3. Decolorize with ethanol
   
   • Removes dye only from Gram negatives
   • Ethanol is ineffective at removing the dye on Gram positives because of their thick cell wall
4. Stain with safranin (pink)
   
   • Colourless Gram negatives become pink, positives remain purple

Question 6

Compare Gram positives and Gram negatives

Answer 6

Gram positives

• Stain purple
• Have a thick periplasm
• Have 1 membrane (cytoplasmic membrane)
• Endospores

Gram negatives

• Stain pink
• Have a thin periplasm
• Have 2 membranes (cytoplasmic membrane and ‘outer membrane’)
• Have a lipopolysaccharide (endotoxin - released when cell desintigrates)

Question 7

What is the cell envelope?

Answer 7

The cell envelope includes the cytoplasmic membrane and everything outside of it (ex., cell wall/periplasm, outer membrane if present)

Question 8

What is the function of periplasms?

Describe their structure/composition

Why are they significant?

Answer 8

Cell walls are a rigid structure around bacteria; prevent osmotic lysis due to overabundance of fluid

• Composed of 2 sugars
• Composed of 1 N-acetyl glucosamine (G) and muramic (M) acid that alternate G-M-G
• Composed of peptide cross linkages

Cell walls are unique to bacteria –> important targets for ABx

Question 9

What are lipoplysaccharides? (endotoxins; Gram negative)

Answer 9

3 parts that span the outer membrane:

1. O-specific polysaccharide (O-antigen)
   
   • Antigen: our immune system recognises this and develops antibodies
2. A core polysaccharide
3. Lipid A component (disaccharide + fatty acid)
   
   • Innate immunity receptors recognise the bacteria using this component
   • Thus, large amounts can cause a cytokine storm

Question 10

What is the nucleoid?

Answer 10

• The nucleoid has no surrounding membrane and contains (usually) 1 circular chromosome
  
  • Haploid (1 set of chromosome) allows for quick selection of beneficial mutations

Question 11

Outline the 3 types of host-microbe relationships

Answer 11

1. Commensalism: one benefits without helping or hurting the other
2. Mutualism: both benefit (the host and the microbe)
3. Parasitism: one benefits (usually the microbe) at the expense of the other
   
   • Usually these are eukaryotes

Question 12

Describe the surface virulence factors

Answer 12

1. The lipopolysaccharide in Gram negatives
2. Flagella
   
   • Enables chemotaxis
3. Pili/fimbriae and adhesions
   
   • Ex., plaque sticking to teeth
4. Capsules
   
   • These are sugar structures (exopolysaccharides) containing many bacteria
   • Attach to host tissues and protect from host immune system
   • Used in vaccines to trigger immune response
   • Important in the formation of biofilms
5. Endospores (secretion systems) in some Gram positives
   
   • ​Cells within the parent cell that are dormant and highly resistant (to preserve genetic material) –> need autoclaves
   • Found in soil, clostridium (tetanus), milk left out (stinky)

Question 13

Describe the stages of biofilm generation

Answer 13

1. Attachment
   
   • Individual cells attach to a surface and grow
2. Microcolony development
   
   • Cells group and produce the exopolysaccharide (capsule)
3. Biofilm development occurs
   
   • These are organised structures of bacteria
   • Nutrients flood in, waste comes out
4. Maturation
   
   • Grow slowly, thus becoming resistant to ABx treatments
   • Bacteria is released from the top to find a new location to attach to, completing the biofilm cycle

Question 14

Describe the secreted virulence factor exotoxin, 4 types and their functions

In what way are they useful to us?

Answer 14

Exotoxins are secreted by the bacteria; thus bacteria can remain in one place but cause systemic problems

This includes,

1. Hemolysins: destroy red blood cells
2. Toxins that function inside the host cell (ex., tetanus, dihtheria)
3. Extracellular enzymes: destroy tissue, lipids, etc.
4. Superantigens: toxins that turn on the adaptive immune system –> cytokine storm

Inactivated exotoxins can be used as vaccines to produce antibodies