c1.4 - microbiology

Question 1

what are bacterial cell walls made up of

Answer 1

three dimensional mesh of peptidoglycan (muriel), polymer of amino acids + sugars

Question 2

gram staining

Answer 2

technique used to differentiate between gram -ive and gram +ive bacteria

Question 3

process of gram staining

Answer 3

1. stain with crystal violet, remove + rinse with water
2. add iodine solution + rinse after 1 minute
3. alternate washes or ethanol + water for 30 seconds
4. counter stain with red safran in for 1 minute
5. dry + examine sample under microscope

Question 4

gram +ive bacteria

Answer 4

thick peptidoglycan wall + purple after staining

Question 5

why does gram +ive appear purple after staining

Answer 5

thick peptidoglycan wall retains crystal violet when rinsed with alcohol

Question 6

gram -ive bacteria

Answer 6

thin peptidoglycan wall with outer lipopolysaccharide membrane + red/pink appearance after staining

Question 7

why does gram -ive appear red/pink after staining

Answer 7

on ethanol treatment, lipopolysaccharide layer is lost + crystal violet washes away
counter stain safran in stains think peptidoglycan layer red/pink

Question 8

obligate aerobe

Answer 8

organism requiring o2 for metabolism

Question 9

obligate anaerobe

Answer 9

organism that can only survive in environments which lack o2

Question 10

facultative anaerobe

Answer 10

• organism normally respires aerobically
• capable of switching to anaerobic respiration in absence of o2

Question 11

aseptic techniques

Answer 11

range of techniques used to culture microorganisms under sterile conditions in order to minimise contamination

Question 12

basic aseptic techniques

Answer 12

• wipe surface with antibacterial cleaner
• set up bunsen burner nearby ~ convection currents prevent microbes entering culture
• flame inoculating loop + neck of bottles before use
• minimise time that vessels contain bacteria tetris are open
• sterilise all equipment (e.g: use of autoclave)
• wear protective clothing

Question 13

how to culture microorganisms

Answer 13

• sterilise inoculating loop in bunsen flame
• lift dish lid + keep at angle
• transfer bacteria to agar plate using sterile inoculating loop/pipette
• tape on lid at two ends, invert dish + incubate
• in lab, ensure dish is not airtight + do not incubate over 25C to avoid growth of pathogens

Question 14

difference between spread plate + streak plate

Answer 14

spread plate - microorganisms distributed evenly with sterile spreader
streak plate - aims to obtain single colonies by rotating plate to build layers of culture on at least three separate streaks

Question 15

nutrient media

Answer 15

solid or liquid nutrient-rich medium used in cultivation of microorganisms

Question 16

composition of nutrient media

Answer 16

contains carbon source, nitrogen source, water + growth factors (e.g: salts + vitamins)

Question 17

condition used when culturing microorganisms

Answer 17

• optimum temp
• constant pH
• nutrient supply
• aerobic conditions

Question 18

difference between total cell count + viable cell count

Answer 18

in given are of vol, total cell count is total number of cell (living + dead) but viable cell count is total number of living cells

Question 19

how viable cell count is conducted

Answer 19

• add known vol of organisms to agar plate
• incubate plate
• count number of colonies

Question 20

what assumed when conducting viable cell count

Answer 20

one cell gives rise to single colony

Question 21

problem with ‘one cell one colony’ assumption

Answer 21

doesn’t account for clumping of cells in of incolumum
may result in lower estimate of number of cells

Question 22

serial dilution

Answer 22

sequence of dilution, in which dilution factor is constant, used to dilute a stock splution