3.4 Microbiology

Question 1

How is bacteria classified ?

Answer 1

By shape, size and cell wall structure

Question 2

What are the different shapes of bacteria ?

Answer 2

Bacillus, Cocci, Spiral

Question 3

Name a type of bacillus bacteria

Answer 3

Bacillus or Eschericha

Question 4

Name a type of cocci bacteria

Answer 4

Staphylococcus

Question 5

Name a type of spiral bacteria

Answer 5

Spirillum

Question 6

What does gram staining allow ?

Answer 6

Enables you to distinguish between gram positive and gram negative bacteria

Question 7

What are the stages of gram staining ?

Answer 7

Use crystal violet reagant as basic dye, Iodine to flood slide, acetone to decolourise and safranin as a counter stain

Question 8

What does crystal violet do in the gram staining process ?

Answer 8

Binds to peptidoglycan so all bacteria stains purple

Question 9

What does iodine do in the gram staining process ?

Answer 9

Acts as a mordant binding crystal violet to peptidoglycan more strongly

Question 10

What does acetone alcohol do in gram staining process ?

Answer 10

Acts as a decolouriser removing unbound crystal violet and lipopolysaccharide

Question 11

What is the purpose of safranin in gram staining ?

Answer 11

Acts as a counter stain

Question 12

What colour does gram positive bacteria stain ?

Answer 12

Purple

Question 13

What are the features of gram positive bacteria ?

Answer 13

Thick peptidoglycan layer
Cell membrane
No lipopolysaccharide layer so susceptible to penicillin and lysozyme enzyme

Question 14

What colour does gram negative bacteria stain ?

Answer 14

Pink/Red

Question 15

What are the features of gram negative bacteria ?

Answer 15

Lipopolysaccharide, peptidoglycan and cell membrane layers

Question 16

What is the purpose of the lipopolysaccharide layer ?

Answer 16

Protect the cell

Question 17

What are the different types of culture medium ?

Answer 17

Defined
Undefined
Selective
Complete

Question 18

What is a defined culture medium ?

Answer 18

Only contains known ingredients

Question 19

What is an undefined culture medium ?

Answer 19

Contains components that are not all known

Question 20

What is a selective culture medium ?

Answer 20

Only allows certain bacteria to grow

Question 21

What is a complete culture medium ?

Answer 21

Contains all chemicals needed to support growth

Question 22

What is required for bacteria growth ?

Answer 22

Carbon
Glucose
Nitrogen
Vitamins
Minerals
25-45 degrees, optimum 37
pH 7.4
Oxygen

Question 23

What are the 3 different types of bacteria ?

Answer 23

Facultative anaerobes
Obligate aerobes
Obligate anaerobes

Question 24

What is a facultative anaerobe ?

Answer 24

Bacteria that grows best with oxygen but can survive without

Question 25

What is an obligate aerobe ?

Answer 25

Bacteria that requires oxygen

Question 26

What is an obligate anaerobe ?

Answer 26

Bacteria that cannot grow in the presence of oxygen

Question 27

What is aseptic technique ?

Answer 27

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

Question 28

What methods can be used to measure growth ?

Answer 28

Direct counting of cells Indirect measurement

Question 29

What are the 2 ways to directly count cells ?

Answer 29

Viable counts Total counts

Question 30

What is a viable count ?

Answer 30

Count colonies of living cells

Question 31

What is a total count ?

Answer 31

Using a haemocytmeter

Question 32

How do you indirectly measure growth ?

Answer 32

By measuring the turbidity of a culture

Question 33

What is turbidity ?

Answer 33

Cloudiness

Question 34

How do you plate and count colonies ?

Answer 34

Count number of cells in small sample of culture Viable count - live cells

Question 35

How do you calculate population size ?

Answer 35

(Number of colonies X Dilution factor ) Divided by Volume of sample