intro to medical microbiology

Question 1

How are bacteria named, use example of E.coli?

Answer 1

• genus first, then species
• underline or italics
• Can abbreviate, so Escherichia coli becomes E. coli

Question 2

Describe prokaryotes structure (bacteria)

Answer 2

• no nucleus or membrane bound organelles
• single, circular DNA (haploid)
• 70S ribosomes (50S and 30S subunits)
• peptidoglycan cell wall

Question 3

Describe eukaryotes

Answer 3

• membrane bound nucleus
• chromosomes in nucleus (diploid)
• 80S ribosomes (60S and 40S subunits)
• no cell wall (except plants and fungi)

Question 4

How are bacteria often classified?

Answer 4

by shape and staining

Question 5

Describe how shape of bacteria is used to classify them

Answer 5

• ROUND = coccus/cocci
• LONG = bacillus/bacilli
• a few are spiral/branched/comma shaped

Question 6

What is the difference between gram positive and gram negative bacteria?

Answer 6

GRAM POSITIVE: no outer
membrane
GRAM NEGATIVE: outer membrane

Question 7

What is the predominant stain used to classify bacteria and what are the results?

Answer 7

• Gram stain
• positive = purple
• negative = pink

Question 8

Describe Gram positive bacteria?

Answer 8

• thick peptidoglycan layer
• lipoteichoic and teichoic acid
• inner cytoplasmic membrane

Question 9

Describe Gram negative bacteria?

Answer 9

• outer membrane made of lipopolysaccharide and has protein channels (porins)
• thin peptidoglycan
• inner cytoplasmic membrane

Question 10

What are the synthetic pathways for peptidoglycan?

Answer 10

• polymerisation of sugars
• elongation of amino acid side-chains
• transpeptidase

Question 11

Why are the synthetic pathways of peptidoglycan important in medicine?

Answer 11

as all the steps are targeted by important classes of antibiotics

Question 12

What does each synthetic pathway for peptidoglycan synthesis do?

Answer 12

• POLYMERISATION OF SUGARS: to make the back-bone
• ELONGATION OF AA SIDE CHAINS: to add the peptides
• TRANSPEPTIDASE: to cross-link

Question 13

Describe the peptidoglycan layer in bacteria?

Answer 13

• SUGARS: glucosamine (NAG) and muramic acid (NAM)
• amino acid peptides, resistant to enzymatic destruction
• cross-linked by transpeptidase enzymes

Question 14

Describe lipopolysaccharide in gram negative bacteria

Answer 14

• lipid A = long-chain fatty acid anchor (active component)
• core polysaccharide chain
• variable CHO chain (= O antigen)

Question 15

Why is lipopolysaccharide in gram negative bacteria important?

Answer 15

• major structural component
• effective permeability barrier (including to antimicrobials)
• regulates host immune response

Question 16

Which patterns of growth can be seen in bacteria?

Answer 16

• MICROSCOPE: in clusters or chains
• SOLIDE CULTURE MEDIUM: colonies are different sizes/shapes

Question 17

How can bacterial growth be exploited to identify the pathogen?

Answer 17

• patterns of growth
• excrete enzymes, waste products
• different requirements for growth (atmosphere ad nutrients)

Question 18

What are the 3 possible bacterial atmospheric requirements?

Answer 18

• aerobes
• anaerobes (obligate anaerobes)
• facultative anaerobes

Question 19

Describe aerobe bacteria?

Answer 19

use oxygen as final electron acceptor (very efficient)

Question 20

Describe anaerobe (obligate anaerobes) bacteria?

Answer 20

• fermentation, final electron acceptor is organic molecule
• okay when substrates are plentiful
• oxygen usually toxic to them

Question 21

Describe facultative anaerobe bacteria

Answer 21

can switch between aerobic and anaerobic metabolism

Question 22

What are some things bacteria can’t make themselves?

Answer 22

• purine and pyrimidines
• amino acid
• vitamins

Question 23

What are the nutritional requirements for E. coli?

Answer 23

• needs glucose and inorganic salts only
• very easy to grow in lab

Question 24

What are the nutritional requirements for Treponema pallidum (syphilis)?

Answer 24

• specialised enriched medium
• hard to grow

Question 25

Describe capsules in bacteria

Answer 25

- polysaccharide coat - 'hides' immunogenic cell wall - metabolic burden on the bacterium - grants virulence - immunity requires antibodies to the capsule

Question 26

Describe the ribosomes in bacteria

Answer 26

- engines of protein synthesis - 70S (50S and 30S subunits) - each contains bacterial RNA and proteins - the RNA is the target of antibiotics and diagnostic tests

Question 27

Why do bacteria move?

Answer 27

chemotaxis (moving towards or away from chemical stimuli)

Question 28

How do bacteria move?

Answer 28

- rotate a flagellum like a propeller - use a pilus like a grappling hook - corkscrew motility (spirochete)

Question 29

How do bacteria stick?

Answer 29

adhesin and receptor bind in a specific/complementary manner

Question 30

What is docking and anchoring in bacteria?

Answer 30

- DOCKING: non-specific adherence - ANCHORING: specific adherance

Question 31

How do bacteria transfer genes?

Answer 31

- transduction - conjugation - competence/transformation

Question 32

What are the mobile genetic elements of bacteria and what do they do?

Answer 32

- plasmids - transposons - they code for toxins and antibiotic resistance genes

Question 33

Describe plasmids

Answer 33

- circular 'extra-chromosomal' DNA - independently replicating - passed down to offspring - some transmitted between bacteria

Question 34

Describe transposons?

Answer 34

- DNA sequences that are able to move location in the genome - encode transposase and other genes

Question 35

What are transposons mobile between?

Answer 35

- genomic and plasmid DNA - plasmids

Question 36

State the 4 phases of bacterial growth

Answer 36

- lag phase - exponential phase - stationary phase - death phase

Question 37

Describe the lag phase in bacterial growth

Answer 37

- no increase in cell numbers - adjustment to new environment - gene regulation

Question 38

Describe the exponential phase in bacterial growth

Answer 38

- cell doubling - slope of the curve = growth rate of organism in that environment

Question 39

Describe the stationary phase in bacterial growth

Answer 39

- nutrients become depleted - metabolites build up - divison stops - gene regulation

Question 40

Describe the death phase in bacterial growth

Answer 40

- exhaustion of resources - toxicity of environment

Question 41

In which phases of bacterial growth does gene regulation occur?

Answer 41

in the lag phase and stationary phase

Question 42

What are endotoxins?

Answer 42

lipopolysaccharides found in the cell wall of Gram-negative bacteria

Question 43

What are the steps to carrying out a gram stain?

Answer 43

1. crystal violet 2. iodine 3. decolourisation with alcohol 4. safranin counterstain

Question 44

What sugars are in the peptidoglycan?

Answer 44

- glucosamine (NAG) - muramic acid (NAM)

Question 45

What is the other stain that can be used and in which context is it used?

Answer 45

- Ziehl-Neelsen stain - for mycobacteria that have thick lipid membrane made of mycolic acids

Question 46

What are some bacterial growth requirements that are modified in the lab?

Answer 46

- temperature - pH - salt content

Question 47

Give examples of bacteria that lack a cell wall and are not 'free-living'

Answer 47

- mycoplasma - chlamydia

Question 48

What are spores resistant to?

Answer 48

- drying - temperature - disinfection - digestion

Question 49

Which medically important bacteria make spores?

Answer 49

- bacillus spp - clostridium

Question 50

What is gene regulation important for in bacteria?

Answer 50

1. conserve energy (prevent unnecessary gene expression) 2. Adapt to environmental changes 3. coordinated changes in expression of multiple genes