Cultures

Question 1

reasons for culturing microorganisms

Answer 1

cant see with naked eye
-investigating to diagnose disease or scientific experiment

Question 2

what does culturing involve

Answer 2

growing large numbers of microorganisms so they can be measured in some way

Question 3

conditions for culturing microorganisms

Answer 3

provided with right level of nutrients and oxygen with ideal pH and temperature

Question 4

why should you take care when culturing microorganisms

Answer 4

-even if microorganisms are planning to culture harmless there is risk of mutant strain arising that may be pathogenic
-risk of contamination of culture by pathogenic microorganism from enviorement
-when you grow strain of microorganism, entry of other microorganisms from air or skin into culture contaminate it

Question 5

health and safety conditions for culturing organisms

Answer 5

-all equipment must be sterile
-once culture has grown it doesnt leave lab
-all cultures disposed of safely be sealing them in plastic bags and sterilising at 121 for 15 mins under high pressure
-no ethical issues of handling microorganisms but danger of infecting other people with pathogens risk

Question 6

steps of culturing

Answer 6

-decide on microorganisms you want to culture and obtain them
-need nutrients to grow
-good source of carbon and nitrogen
-nutrient medium can be broth or agar
-solid and liquid media kept sterile until ready for use

Question 7

what is agar jelly

Answer 7

jelly extracted from seaweed

Question 8

why is agar jelly useful

Answer 8

although it sets as jelly at 50 degrees id doesnt melt again until heated to 90 degrees

Question 9

what microorganisms need to grow in culture

Answer 9

-some can grow on pure agar
-most need added nutrients
-medium enriched with protein like blood or meat extract or yeast extract

Question 10

selective medium

Answer 10

-medium in or on which only select group of microorganisms with those particular requirements will grow

Question 11

why is selective media important

Answer 11

important in identifying particular mutant strains of microorganism and antibiotic resistance

Question 12

YM media

Answer 12

low pH which encourages growth of fungi and moulds but discourages bacteria

Question 13

MacConkey agar

Answer 13

designed to grow gram negative bacteria

Question 14

how can selective media identify microorganisms that have been genetically modified

Answer 14

-because antibiotic resistance or requirement for particular nutrient engineered with desired gene as marker

Question 15

2 steps for preparing culture

Answer 15

-once suitable medium prepared introduce microorganisms

Question 16

inoculation

Answer 16

getting bacteria onto agar and into broth

Question 17

whats an inoculating loop

Answer 17

scraping off bacteria from one solid media surface either into liquid medium
streaking across another solid medium plate

Question 18

inoculating broth

Answer 18

-involves making suspension of bacteria to be grown and mixing in known volume with sterile nutrient broth in flask

Question 19

what to do with flask after inoculation

Answer 19

-stoppered with cotton wool quickly to prevent contamination from air and labelled to make sure broth is aerated allowing oxygen to growing bacteria

Question 20

inoculating solid media

Answer 20

sterilise inoculating loop by holding it in bunsen burner until glowing hot read and leave it to cool
-dip loop in suspension of bacteria- streak loop across surface of agar avoiding digging into agar
-replace petri dish lid, tape closed and label and turn dish upside down

Question 21

how to to get pure culture of single type of organism

Answer 21

isolation

Question 22

pure culture with and without oxygen

Answer 22

-anaerobic conditions ensures only anaerobic bacteria will survive
-growing organisms with oxygen means only aerobic organisms can survive
-some bacteria may grow under both conditions
-not allow to complete separation of microorganisms necessary for pure culture but reduced variety

Question 23

growing pure cultures and nutrients

Answer 23

produce medium for organism desired and inhibit growth of others
-allows identification of colony you want to re-inoculate for single pure culture
-need to control range of nutrients available or introduce selective growth inhibitors or antifungal chemicals that will reduce growth of microorganisms

Question 24

indicator media for pure cultures

Answer 24

-indicator media that cause certain bacteria to change colour
-colonies that change colour or dont can be isolated and cultured

Question 25

what is it important to isolate biologically

Answer 25

-isolate disease causing organisms from those of normal body flora
-so diagnosis can be made and treatment planned

Question 26

how to count bacteria and single celled fungi cultured in nutrient broth

Answer 26

-directly using microscope and a haemocytometer

Question 27

whats a haemocytometer

Answer 27

-has specialised thick microscope slide with rectangular chamber that holds standard volume of liquid 0.1mm3
-chamber is engraved with a grid of lines

Question 28

how to count cells with haemocytometer

Answer 28

grid has square divided into 16 smaller squares
-number of cells in each of four sets of 16 counted and mean taken

Question 29

haemocytometer being calibrated

Answer 29

number of bacterial or fungal cell in one set of 16 squares equated to number of cells of broth
-enables you to calculate number of microorganisms in standard volume of broth

Question 30

turbidimetry

Answer 30

specialised form of colorimetry

Question 31

turbid

Answer 31

cloudy looking as number of bacterial cells in culture increase

Question 32

what happens as solution becomes more turbid

Answer 32

absorbs more light so less light passes through it

Question 33

function of colorimeter

Answer 33

-measures how much light passes through sample showing how much light is absorbed and shows how many microorganisms present

Question 34

how is a calibration curve produced

Answer 34

-by growing a control culture and taking samples at regular time intervals

Question 35

what can the calibration curve be used for

Answer 35

we can measure the number of microorganisms by using turbidimetry
-also can investigate the effect of different conditions on growth rate of microorganism