Internal and External Structures

Question 1

What are the internal structures common to bacteria?

Answer 1

Cell wall and membrane, nucleoid and plasmids, ribosomes, inclusion bodies and spores

Question 2

What are the external structures common to bacteria?

Answer 2

Flagella, pili, glycocalyx

Question 3

Describe cell wall and membrane and how it’s targeted by anti microbial agents

Answer 3

• cell wall provides structural support and protection
• gram pos = thick peptidoglycan layer
• purple when stained with crystal violet, followed by iodine, and finally safranin
• antimicrobial agents target cell wall synthesis by inhibiting enzymes that synthesise peptidoglycan (vancomycin)
  -gram neg = thin peptidoglycan layer and outer lipopolysaccharide membrane
• outer membrane provides protection against antibiotics
• antibiotics target peptidoglycan synthesis (fosfomycin)

Question 4

Describe nucleoid and plasmids

Answer 4

Nucleoid - genetic material, contains bacterial chromosome
Plasmids - small, circular, extrachromosomal DNA molecules
Antimicrobial agents target by inhibiting replication/transcription

Question 5

Describe ribosomes

Answer 5

Ribosomes - ribosomal RNA + proteins
- responsible for protein synthesis
- antimicrobial agents (erythromycin) inhibit protein synthesis

Question 6

Describe inclusion bodies

Answer 6

• storage granules that accumulate glycogen, polyphosphate granules
• antimicrobial agents affect metabolic pathways involved in their formation

Question 7

Describe endospores

Answer 7

Highly resistant, thick layers
- result from nutrient depletion
- highly resistant to heat, chemicals and antibiotics
- sporicidal chemicals/extreme heat

Question 8

Describe flagella

Answer 8

Tail like appendage that allows cell motility
Enables cell to move towards favourable conditions and away from harmful ones

Question 9

Pili

Answer 9

Hair like projections
- allow adhesion to surfaces/host cells
- antimicrobial agents bind to pili and prevent adhesion/colonisation

Question 10

Glycocalyx

Answer 10

• layer of polysaccharides external to cell wall
  -provides protection, helps evade detection
• antibiotics interfere with formation/disrupt integrity

Question 11

Describe the staining method for gram positive and gram negative bacterial cell walls

Answer 11

A gram stain is performed to identify Gram pos from Gram neg bacteria
Gram positive = purple staining
Gram negative = pink staining
Bacteria stained with crystal violent dye and then rinsed. Then followed with iodine and rinsed. Then finally stained with safranin and rinsed.

Question 12

Describe a staining method for endospores

Answer 12

Treat spores with malachite green dye and rinse
Treated with safranin after and rinse
Spores retain green colour from malachite