Lecture 2: Introduction to medical microbiology

Question 1

What is the difference between gram negative and gram positive bacterial organisms?

Answer 1

Gram-negative (PINK) bacterium have a thin layer of peptidoglycan plus an lipopolysaccharides membrane with porins. Gram positive bacterium have only a thick layer of peptidoglycan.

Question 2

What colour to gram negative bacterium stain?

Answer 2

Pink

Question 3

What colour to gram positive bacterium stain?

Answer 3

Purple

Question 4

What is the structure of peptidoglycan?

Answer 4

Peptidoglycans are composed of N-acetylated sugars and amino acid peptides which are resistant to enzymatic destruction. Cross-linked by transpeptidase enzymes

Question 5

How is the peptidoglycan structure of bacterium cell membranes used as a target for antibiotics?

Answer 5

Cross-linked N-acetylated sugars and amino acid peptides in peptidoglycans are targets for antibiotics.

Question 6

What is the structure of lipopolysaccharide (LPS)?

Answer 6

LPS is composed of lipid A, core polysaccharide chain and variable CHO chains.

Question 7

What is the importance of LPS in gram negative bacterium?

Answer 7

LPS is a major structural component in Gram negative bacteria and it is also responsible for effecting the permeability of the barrier and modulating host immune response.

Question 8

What are the atmospheric requirements of aerobic bacteria?

Answer 8

Use O2 as final electron acceptor to oxidise glucose to CO2 and H2O and generate energy.

Question 9

What are the atmospheric requirements of anaerobic bacteria?

Answer 9

Use fermentation to convert glucose to lactic acid and generate energy.

Question 10

What are the atmospheric requirements of facultative aerobic bacteria?

Answer 10

Can switch between aerobic and anaerobic metabolism to generate energy.

Question 11

What factors effect bacterial growth?

Answer 11

Atmospheric conditions, temperature, pH, and salt content.

Question 12

What is the purpose of the bacterial capsule?

Answer 12

Polysaccharide capsule coat ‘hides’ immunogenic cell wall of bacteria from the immune system and confers virulence. Metabolic burden on bacteria.

Question 13

What is the purpose of the bacterial ribosomes?

Answer 13

Responsible for bacterial protein synthesis to allow for propagation

Question 14

How do bacteria move?

Answer 14

Bacteria can move via chemotaxis which is movement towards or away from a chemical stimuli. Bacteria can also use flagella, pili and adhesins to aid in movement.

Question 15

What is chemotaxis?

Answer 15

Movement towards or away from a chemical stimuli.

Question 16

How do bacteria stick to host cells?

Answer 16

1. Non-specific adherence “docking”
2. Specific adherence “anchoring”
3. Biofilm formation

Question 17

What features of bacteria aid in the binding to host cells?

Answer 17

Adhesin and receptors which bind in a specific and complementary manner to the host cells

Question 18

What is the purpose of the bacterial mobile genetic elements (plasmids and transposons)?

Answer 18

plasmids are circular ‘extra-chromosomal’ DNA that independently replicate and carry a number of genes that confer specific traits and can confer antibiotic resistance.

Transposons are DNA sequences that are able to move in the genome and encode transposases and other genes.

Question 19

How do bacteria replicate genetic material?

Answer 19

Conjugation

Question 20

What is the purpose of the bacterial spores?

Answer 20

Non-replicating dormant form of bacteria that can propagate and facilitate reinfection of bacterial disease

Question 21

How do bacteria regulate gene expression?

Answer 21

Bacteria use quorum sensing to allow them to conserve energy and prevent unnecessary gene expression.

Question 22

What are the 4 phases of bacterial cell growth?

Answer 22

1. Lag Phase
2. Exponential Phase
3. Stationary Phase
4. Death Phase

Question 23

What happens during the lag phase of bacterial cell growth?

Answer 23

No increase in cell numbers and adjustment to new environment by gene regulation.

Question 24

What happens during the exponential phase of bacterial cell growth?

Answer 24

Rapid cell replication

Question 25

What happens during the stationary phase of bacterial cell growth?

Answer 25

Nutrients become depleted, metabolites build up and division stops. Controlled by gene regulation.

Question 26

What happens during the death phase of bacterial cell growth?

Answer 26

Exhaustion of resources and toxicity of environment.