Bacterial Growth, Nutrition and Identification

Question 1

List 10 criteria for bacterial classification.

Answer 1

1 - Gram stain.

2 - The proportion of the genome formed of guanine + cytosine.

3 - Growth temperature.

4 - Ability to form heat stable spores.

5 - Electron acceptors for respiration.

6 - Photosynthetic ability.

7 - Motility.

8 - Morphology.

9 - Ability to use various carbon and nitrogen sources.

10 - Special nutritional requirements.

Question 2

List the taxonomic hierarchy for the three-domain system.

Answer 2

1 - Domain.

2 - Kingdom.

3 - Division.

4 - Class.

5 - Order.

6 - Family.

7 - Genus.

8 - Species.

Question 3

List 7 methods of identification of bacteria.

Answer 3

1 - Antibiotic susceptibility.

2 - Whole genome sequencing.

3 - Microscopic morphology.

4 - Antigenic properties.

5 - Cultural characteristics.

6 - Biochemical reactions.

7 - Typing.

Question 4

List the steps involved in gram staining.

Answer 4

1 - Application of crystal violet.

2 - Application of iodine (mordant).

3 - Alcohol wash (decolourisation).

4 - Application of safranin (counterstain).

Question 5

What is the function of a mordant?

Answer 5

To fix the dye to the bacteria.

Question 6

How do gram positive and negative bacteria stain?

Answer 6

• Gram positive stain purple (retain the dye).

- Gram negative stain pink (lose the dye upon decolourisation).

Question 7

What does the term ‘coccus’ tell you about the morphology of a bacterium?

Answer 7

Indicates a round shape / clusters.

Question 8

What does the term ‘bacillus’ tell you about the morphology of a bacterium?

Answer 8

Indicates a rod-like shape.

Question 9

List 3 properties of Staphylococcus aureus.

Answer 9

1 - Gram positive.

2 - Coccus.

3 - Aerobic.

Question 10

List 3 properties of the Clostridium species.

Answer 10

1 - Gram positive.

2 - Bacillus.

3 - Anaerobic.

Question 11

List 3 properties of B. fragilis.

Answer 11

1 - Gram negative.

2 - Bacillus.

3 - Anaerobic.

Question 12

List 3 properties of the shigella family of bacteria.

Answer 12

1 - Gram negative.

2 - Bacillus.

3 - Aerobic.

Question 13

List 3 properties of Streptococcus pneumoniae.

Answer 13

1 - Gram positive.

2 - Coccus.

3 - Anaerobic.

Question 14

List 3 properties of Neisseria gonorrhoeae.

Answer 14

1 - Gram negative.

2 - Diplococcus.

3 - Aerobic.

Question 15

What are higher bacteria?

Answer 15

Bacteria with a relatively complex organisation.

Question 16

List 2 examples of higher bacteria and the disease caused by each.

Answer 16

1 - Mycobacterium tuberculosis (causes TB).

2 - Mycobacterium leprae (causes leprosy).

Question 17

Define acid-fast bacteria.

What makes bacteria acid-fast?

Answer 17

• Bacteria that are resistant to decolourisation by an acid.

- These bacteria have complex cell walls that contain large amounts of lipid substances known as mycolic acids.

Question 18

Give an example of a genus of bacteria that is acid-fast.

Answer 18

Mycobacterium.

Question 19

What does the term ‘spirochete’ tell you about the morphology of a bacterium?

Answer 19

Indicates a flexible, spirally twisted shape.

Question 20

List 3 properties of Treponema pallidum (syphilis).

Answer 20

1 - Gram negative.

2 - Spirochete.

3 - Aerobic.

Question 21

Why are Mycoplasma pneumoniae resistant to penicillins?

Answer 21

Because they lack peptidoglycan.

Question 22

Why is the Chlamydiae phylum of bacteria known as obligate intracellular parasites?

Answer 22

Because they require host ATP (hence obligate intracellular).

Question 23

Define bacterial growth.

Answer 23

The orderly increase in the sum components of an organism (not an increase in cellular size!).

Question 24

List the phases of growth for bacteria.

Answer 24

1 - Lag.

2 - Log.

3 - Stationary.

4 - Death.

Question 25

Define dry cell weight.

Answer 25

The weight left when a cell's water content has been removed by heating.

Question 26

What is most bacterial dry weight comprised of?

Answer 26

Organic matter comprised of macromolecules linked by anhydride bonds.

Question 27

List 2 sources of energy for medically relevant bacteria.

Answer 27

1 - Fermentation, e.g. of sugars. 2 - Respiration.

Question 28

List 2 sources of carbon for bacteria.

Answer 28

1 - CO2. 2 - Organic carbon, e.g. glucose.

Question 29

What is the primary source of nitrogen for bacteria?

Answer 29

Ammonia (e.g. in soil).

Question 30

List 2 sources of sulphur for bacteria.

Answer 30

1 - Dissolved sulphate. 2 - Found in cysteinyl and methionyl side chains of proteins.

Question 31

Give an example of a use of sulphur in bacteria.

Answer 31

Used to form co-enzymes.

Question 32

List 4 uses of phosphorus.

Answer 32

1 - Required for ATP production. 2 - Required for nucleic acid production. 3 - Required to phosphorylate proteins. 4 - Required for coenzymes such as NADP.

Question 33

What is the primary use of minerals (such as Mg2+, Ca2+ and Fe2+) in bacteria?

Answer 33

Enzyme function.

Question 34

Define siderophore.

Answer 34

A molecule present in microorganisms that facilitates iron uptake.

Question 35

At which pH do most microorganisms grow best?

Answer 35

6-8.

Question 36

At which temperature do most pathogenic bacteria grow best?

Answer 36

30-37 degrees celsius.

Question 37

Define facultative anaerobe.

Answer 37

Bacteria that can grow in both the presence or absence of oxygen.

Question 38

Why do most microbes express superoxide dismutase and catalase?

Answer 38

- To manage oxygen toxicity: - Catalase converts hydrogen peroxide (H2O2) into water and oxygen. - Superoxide dismutase converts superoxide (O2-) into H2O2, which must be broken down by catalase.

Question 39

What type of molecule is agar? Why is it used as a medium for bacterial growth?

Answer 39

- A polysaccharide. | - It is used as a medium for bacterial growth as it is resistant to antibiotic action.

Question 40

Define differential media.

Answer 40

Media that distinguish bacterial species from each other.

Question 41

Give an example of a differential media.

Answer 41

Blood agar (indicates which bacteria are haemolytic).

Question 42

Define selective media.

Answer 42

Media that suppress the growth of unwanted bacteria that may be in the same sample.

Question 43

List 2 examples of media that are both selective and differential. Explain how they work as selective and differential media.

Answer 43

1 - Mannitol salts agar (selective for gram positive bacteria, and bacteria that ferment mannitol show as yellow). 2 - MacConkey agar (selective for gram negative bacteria, and bacteria that ferment lactose show as pink).

Question 44

How does alpha haemolysis appear differently on a blood agar culture to beta haemolysis?

Answer 44

- Alpha-hemolysin partially breaks down the red blood cells, leaving a greenish color behind. - Beta-hemolysin breaks down the red blood cells and hemoglobin completely, leaving a clear zone around the bacterial growth.

Question 45

List 2 examples of antimicrobial agents that are used against specific bacterial species. For each agent, include the name of the bacterial species for which it is used.

Answer 45

1 - Optochin and Streptococcus pneumoniae. 2 - Bacitracin and Streptococcus pyogenes. * These agents are not used for therapy.

Question 46

Define typing.

Answer 46

The identification of certain strains of bacteria within a species that possess particular pathogenic properties.