Microbiology

Question 1

Three shapes to identify bacteria:

Answer 1

Coccus - spherical
Bacillus - rod shaped
Spirillum -spiral

Question 2

Three ways to name groupings of bacteria:

Answer 2

Diplo - Paired
Staphyl - Clousters
Strepto - Chains

Question 3

What colour will a gram positive bacteria be stained?

Answer 3

Purple

Question 4

What colour will a gram negative bacteria be stained?

Answer 4

Red

Question 5

Why is gram positive bacteria stained purple?

Answer 5

It has thick peptidoglycan layer. Retains the crystal violet complex which stains it purple.

Question 6

Why is gram negative bacteria stained red?

Answer 6

Thinner peptidoglycan and lipopolysaccharide which is dissolved by alcohol. So purple stain is washed away but is stained red due to safranin.

Question 7

Preparation of Gram Stain:

Answer 7

Crystal Violet (All stained purple)
Iodine (Binds Cv to peptidoglycan more strongly)
Alcohol (removes unbound CV and lipopolysaccharide)
Counterstain with safranin

Question 8

Obligate aerobes

Answer 8

Need oxygen to grow

Question 9

Obligate anaerobes

Answer 9

Only grow in the absence of oxygen

Question 10

Facultative anaerobes

Answer 10

Can respire anaerobically if they need to

Question 11

Culturing Bacteria:

Answer 11

Sterilise inoculating loop using blue bunsen flame
Dip loop into sample
Use loop to spread droplet of sample in agar plat
Tape lid shut to secure not fully sealed
Incubate plate

Question 12

Aseptic technique prevents :

Answer 12

Contamination of the environment by the microorganisms being handled
Contamination of the bacterial cultures by unwanted microorganisms from the
environment

Question 13

Ways of sterilising equipment:

Answer 13

Autolcave at 121 degrees for 15 mins
Heating an inoculating loop in a bunsen flame
Irradiation

Question 14

Conditions required to grow bacteria:

Answer 14

Carbon source (e.g  glucose)
Nitrogen source 
Sulfur + Phosphorous
Vitamins and Mineral
Suitable pH
Incubated at suitable temp

Question 15

Counting bacteria directly:

Answer 15

By counting each cell

Question 16

Counting bacteria indirectly:

Answer 16

Measuring turbidity

(cloudiness of the culture medium) with colorimeter

Question 17

Types of direct counts

Answer 17

Total and Viable

Question 18

Viable counts

Answer 18

Only count living or actively growing cells

Question 19

Total counts

Answer 19

Both living and dead (may lead to underestimation)

Question 20

Viable count method

Answer 20

A known volume of organisms is added to agar plates.

Assumption that one cell gives rise to one colony.

Question 21

Why we use serial dilution?

Answer 21

To make the counting of colonies more manageable.

Question 22

Serial Dilution method:

Answer 22

1ml of sample added to 9ml of sterile water
1ml of this mixture into 9ml of sterile water etc
10-1,10-2,10-4

Question 23

How to estimate population size

Answer 23

number of colonies
x
dilution factor