Microbiology 3.4

Question 1

What technique is used to differentiate between two bacteria?

Answer 1

Gram staining.

Question 2

What two bacteria does gram staining show?

Answer 2

Gram positive and gram negative.

Question 3

What are the differences between gram positive and gram negative?

Answer 3

Gram negative- Outer membrane, lipoproteins, thin layer of peptidoglycan.

Question 4

What are the similarities between gram positive and negative?

Answer 4

They both have periplasmic space and cytoplasmic membrane.

Question 5

What dyes are used in gram staining?

Answer 5

Safranin- stains cells red
Crystal violet- stains cells purple

Question 6

What is the procedure of gram staining?

Answer 6

Fixation
Crystal violet
Iodine treatment
Decolourisation
Counter stain safranin

Question 7

What colour are gram negative bacteria?

Answer 7

Red.

Question 8

What colour are gram positive bacteria?

Answer 8

Purple.

Question 9

What shape is cocci?

Answer 9

Sphere.

Question 10

What is an example of cocci?

Answer 10

Staphylococci aureus.

Question 11

What shape is bacilli?

Answer 11

Rod.

Question 12

What is an example of bacilli?

Answer 12

Salmonella typhi.

Question 13

What happens in the lag phase?

Answer 13

Bacteria has to climatize to the conditions so there aren’t many live cells.

Question 14

What happens in the log/ exponential phase?

Answer 14

There are many live cells as cells divide by binary fission and double which creates the exponential growth.

Question 15

What happens during the stationary phase?

Answer 15

The bacteria population size mainly stays constant. This is because cells stay metabolically active and waste products begin to accumulate.

Question 16

What happens during the death phase?

Answer 16

Living cells stop metabolic functions and begin to die leaving only few cells viable. This is because waste products grow at a maximum.

Question 17

What does total count mean?

Answer 17

Cells that are alive and dead.

Question 18

What does viable count mean?

Answer 18

Only cells that are living or actively growing.

Question 19

What are three condition that are needed for bacteria to grow on an agar plate?

Answer 19

pH of 6-8, oxygen and water.

Question 20

How are penicillin more effective again gram-positive bacteria than gram negative?

Answer 20

Gram negative bacteria has an outer membrane (lipoproteins), and gram-positive bacteria does not. This leads to the peptidoglycan in the gram-positive bacteria to weaken. This makes them less susceptible to attack by lysozyme and the lipids act as an endotoxin.

Question 21

What are bacterial cell walls made up of?

Answer 21

A three-dimensional mesh of peptidoglycan, a polymer of amino acids and sugars.

Question 22

Define gram positive bacteria.

Answer 22

Bacteria that have a thick peptidoglycan wall.

Question 23

Why are gram positive bacteria purple?

Answer 23

The thick peptidoglycan wall retains crystal violet when rinsed with alcohol.

Question 24

Define gram negative bacteria.

Answer 24

Bacteria that has a thin peptidoglycan wall with an outer lipopolysaccharide membrane.

Question 25

Why are gram negative bacteria red?

Answer 25

When it is treated with alcohol it looses its lipopolysaccharide layer and the crystal violet washes away. The counterstain safranin stains the thin peptidoglycan layer red.

Question 26

What is an obligate aerobe?

Answer 26

An organism that requires oxygen for metabolism.

Question 27

What is an obligate anaerobe?

Answer 27

An organism that can only survive in environments which lack oxygen.

Question 27

What is an obligate anaerobe?

Answer 27

An organism that can only survive in environments which lack oxygen.

Question 28

What is a facultative anaerobe?

Answer 28

An organisms that normally respired aerobically and it is capable of switching to anaerobic respiration in the absence of oxygen.

Question 29

What are aseptic techniques?

Answer 29

A range of techniques used to culture microorganisms under sterile conditions in order to minimise contamination.

Question 30

Basic aseptic techniques:

Answer 30

Wipe surface with antibacterial cleaner, set up Bunsen burner nearby, flame inoculating loop and neck of bottles before use, minimise time that vessels containing bacteria are open, sterilize equipment and wear protective clothing.

Question 31

What is the difference between total cell count and viable cell counts?

Answer 31

In a given area or volume, total cell count is the total number of cells (both living and dead) whereas a viable cell count is the total number of living cells.

Question 32

What is assumed when conduction a viable cell count?

Answer 32

It is assumed that one cell gives rise to a single colony.

Question 33

What is wrong with the one cell one colony assumption?

Answer 33

It does not account for clumping of cells which may result in lower estimate of number of cells.