3.4 - Microbiology

Question 1

What are the 3 main types of shapes in bacteria and an example of each?

Answer 1

Bacillus or rodshaped eg Bacillus
Coccus or spherical eg Staphyloccus
Spiral or corkscrew shaped eg Spirillum

Question 2

Example of single bacteria.

Answer 2

Helicobacter

Question 3

Example of a bacteria in pairs.

Answer 3

DiplococcusE

Question 4

Example of a bacteria in chains.

Answer 4

Streptococcus

Question 5

Example of bacteria in clusters.

Answer 5

Staphylococcus

Question 6

What is a gram stain?

Answer 6

A method of staining the cell walls of bacteria as an aid to their identification
Allows us to distinguish between gram neg and gram pos
Before staining, bacteria are colourless, g+ are stained purple, g- are stained red

Question 7

What does the cell wall do in bacteria?

Answer 7

Peptidoglycan
Provides strength and gives it shape
The wall protects against swelling and bursting from lysis
G+ have a basic structure, whilst G- have an outerlayer of polyscaccharide

Question 8

What are the 4 stages behind gram staining?

Answer 8

Crystal violet reagent - basic dye (Binds to peptidoglycan so all bacteria stain purple)
Lugols iodine - mordant (binds crystal violet to the peptidoglycan more strongly)
Acetone alcohol - decolouriser (removes unbound crystal violet and lipopolysaccharide, g- lose their stain and become colourless, g+ remain purple)
Safranin - counterstain (g- stain red, g+ remains purple)

Question 9

What does it mean the g+ bacteria have no lipopolysaccharide?

Answer 9

No lipopolysaccharide makes them more suseptible to lyzosome and penicillin

Question 10

What does it mean the g- bacteria have lipopolysaccharide?

Answer 10

They are resistant to penicillin and lyzosome
To control them, a different class of antibiotics are required that interfere with protein synthesis

Question 11

How do bacteria reproduce?

Answer 11

Asexually through binary fission every 20 mins

Question 12

What do micro-organisms require for growth?

Answer 12

• nutrients
• vitamins and minerals
• correct temperature (25-45)
• pH alkaline conditions
• oxygen to grow (some can survive without it)

Question 13

What is a defined media?

Answer 13

Contains only known ingrediants

Question 14

What is an undefined media?

Answer 14

Contains components not known

Question 15

What is a selective media?

Answer 15

Allows certain bacteria to grow

Question 16

What is a complete media?

Answer 16

Contains all chemicals needed to support growth

Question 17

What is aseptic technique?

Answer 17

Laboratory practice that maintains sterility in apparatus and prevents contamination of equipment and the environment

Question 18

How does the aseptic technique method prevent contamination?

Answer 18

• sterilise all apparatus
• handle all cultures carefully
  -sterilise work surface
• hold the culture bottle with one hand, remove the cap with little finger of the other hand, do not place cap down on the worksurface
• flame the mouth of the bottle for 2-3 seconds
• pass the inoculating loop through the flame until it is red hot and allow it to cool in the air
• lift the lid of the petri dish just enough to allow entry of the inoculating loop
• secure the petri dish with 2 pieces of tape to prevent anaerobic conditions (growth of pathogens)
• incubate at 25*

Question 19

How can the size of a population be measured?

Answer 19

Directly by counting cells
Indirectly, by measuring the turbidity (cloudiness) of the culture

Question 20

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

Answer 20

• viable counts (living cells only)
• total counts (living and dead)

Question 20

What is a colony?

Answer 20

A cluster of cells, or clone, which arises from a single bacterium or fungal spore by asexual reproduction

Question 21

How are serial dilutions created?

Answer 21

9cm3 water in a test tube
Take 1cm3 of orginal solution and put it in first test tube
Creates a 10-1 solution
Repeat until desired dilution is acquired

Question 22

Why are most bacterial cultures diluted?

Answer 22

So that clumping doesnt occur on the agar plates, so colonies can be counted.

Question 23

What is the equation for a dilution factor?

Answer 23

dilution = 1/conc

Question 24

What is the equation for population size?

Answer 24

population size = number of colonies x dilution factor/ volume of the sample

Question 25

What is a haemocytometer?

Answer 25

It is more accurate than other counting techniques as it uses a specialised microscopic slide called a haemocytometer, result is a total cell count.