3.4 microbiology

Question 1

three shapes of bacteria

Answer 1

bacillus (rod)
coccus (sphere)
spirillus (sprial)

Question 2

other way bacteria can be classified

Answer 2

by the structure of its cell wall

Question 3

how can you distinguish between gram -ve and gram +ve bacteria

Answer 3

gram stain

Question 4

what colour will gram +ve bacteria turn

Answer 4

purple

Question 5

what colour will gram -ve bacteria stain

Answer 5

red

Question 6

why do the bacteria stain different colours

Answer 6

due to the different chemical composition and structure of their cell wall

Question 7

structure of gram +ve bacteria

Answer 7

thick outer wall made of peptidoglycan (murein) with no outer lipopolysaccharide.

Question 8

how does staining work on gram +ve bacteria

Answer 8

stain can bind due to the absence of lipopolysaccharide (also why gram +ve are more susceptible to penicillin and lysozyme

Question 9

how does the structure of gram +ve bacteria allow for purple staining

Answer 9

allows the crystal violet/iodine complex to be retained within the cell-staining the cells purple

Question 10

structure of gram -ve bacteria

Answer 10

thinner peptidoglycan cell wall and an outer lipopolysaccharide membrane

Question 11

what does lipopolysaccharide do to gram-ve bacteria

Answer 11

protects the peptidoglycan so they are not affected by lysozymes or penicillin. a different class of antibiotics must be used instead

Question 12

explain the staining of gram negative cells

Answer 12

gram negative cell walls lose the outer lipopolysaccharide membrane and the thin peptidoglycan walls allow the purple stain complex to be washed away. gram negative cells are not stained by the gram stain (remain colourless) but stain red after counter-staining with safranin

Question 13

what are the stage of staining

Answer 13

fixation
crystal violet
iodine treatment
decolorisation
counter stain with safranin

Question 14

explain crystal violet

Answer 14

crystal violet is the basic dye that binds to peptidoglycan

Question 15

peptidoglycan

Answer 15

=meurin

Question 16

explain iodine treatment

Answer 16

iodine makes the crystal violet bind more strongly to the peptidoglycan

Question 17

explain decolorisation

Answer 17

acetone- alcohol decolourises the gram -ve bacteria as it removes unbound crystal violet and the lipopolysaccharide layet

Question 18

explain counter-stain with safranin

Answer 18

safranin is used as a counter-stain, it stains the gram -ve bacteria red

Question 19

what do bacteria have different of

Answer 19

oxygen requirements

Question 20

three different types of bacteria (oxygen requirements)

Answer 20

obligate anaerobe
obligate aerobe
facultative anaerobe

Question 21

explain growth of an obligate aerobe

Answer 21

growth is inhibited in the absence of oxygen

Question 22

explain growth of an obligate anaerobe

Answer 22

growth is inhibited in the presence of oxygen

Question 23

explain growth of a facultative anaerobe

Answer 23

grows best in the presence of oxygen. but can respire anaerobically if they need to

Question 24

what would a tube where bacteria was clustered at the top of the tube show

Answer 24

they need oxygen for respiration and growth. their growth is inhibited in the absence of oxygen, they must be obligate aerobes

Question 25

what would a tube where bacteria was clustered at the bottom of the tube show

Answer 25

bacteria found away from the source of oxygen, they must be obligate anaerobe

Question 26

what would a tube where bacteria was spread throughout the tube show

Answer 26

spread throughout but mainly found towards the top. these bacteria can grow in the absence of oxygen, but grow best with oxygen, they are facultative anaerobes

Question 27

what conditions are needed for micro-organisms growth (culturing conditions)

Answer 27

nutrient (glucose and nitrogen) vitamins and mineral salts temperature pH oxygen

Question 28

why is glucose needed for culturing where would you use it

Answer 28

needed for respiration can be in the broth (liquid medium) or agar (solid)

Question 29

why is nitrogren needed for culturing where would you use it

Answer 29

nucleic acid, amino acid synthesis in organic molecules and in organic forms (nitrate ions)

Question 30

why are vitamins and mineral salts needed for culturing what would you use

Answer 30

growth factors vitamins e.g. biotin mineral salts e,g, Na+

Question 31

why is optimum temperature needed for culturing optimum?

Answer 31

25/45 degrees enzymes regulate bacterial metabolism optimum is 25/45 with mammalian pathogens at 37

Question 32

why is optimum pH needed for culturing

Answer 32

most bacteria favour slightly alkaline conditions (pH) fungi grow better in slightly acidic conditions

Question 33

why is oxygen temperature needed for culturing

Answer 33

needed for respiration

Question 34

what are aseptic techniques used for

Answer 34

to prevent; -contamination of the environment by the microorganisms being handled -contamination of the bacterial cultures by unwanted microorganisms from the environment

Question 35

examples of sterilisation

Answer 35

- passing metal transfer tools (inoculating loop) through a roaring/blue bunsen flame until they glow red -using pre-sterilised petri dishes -sterilising any glassware used under high pressure and high temperature

Question 36

how to pour a sterile agar plate using aseptic techniques

Answer 36

-open the culture bottle cap using your little finger and do not place the cap or bottle on the bench -flame the neck of the bottle in a blue bunsen flame -work close to the bunsen flame as the updraft helps prevent contamination -open the sterile petri dish lid at an angle -pour in the molten agar and close lid immediately. swirl gently to remove air bubbles -secure lid with tape

Question 37

how can you count bacteria grown in a liquid culture

Answer 37

can be counted directly (by counting each cell) or indirectly (by measuring tubidity)

Question 38

what is the turbidity

Answer 38

cloudiness of the culture medium

Question 39

how do you measure the turbidity

Answer 39

using a colorimeter

Question 40

what are the 2 types of direct counts

Answer 40

total counts viable counts

Question 41

what does the total count refer to

Answer 41

include both living and dead cells

Question 42

what does the viable count refer to

Answer 42

only count living or actively growing cells and therefore underestimate population cells

Question 43

viable count method

Answer 43

counts cells which are unable to grow into visible colonies on an agar plate. serial dilution is used if the population density of the sample is too high to count,

Question 44

what is a colony

Answer 44

cluster of cells arising from a single bacterium or fungal spore

Question 45

what is a pathogen

Answer 45

a microogranism that causes disease in its host

Question 46

what is aseptic techniques

Answer 46

laboratory practice thatmaintains sterility of apparatus and prevents contamination

Question 47

what can we work out from counting the colonies

Answer 47

work out the original number of bacteria in our sample