3.4 microbiology

Question 1

what are the 3 classifications of bacteria?

Answer 1

coccus (circular)
bacillus (rod shaped)
spirillum (curved forms)

Question 2

what are the 3 circular bacteria?

Answer 2

diplococcus (pairs)
streptococcus (chains)
staphylococcus (clusters)

Question 3

what are the 3 rod shaped bacteria?

Answer 3

coccobacilli (oval)
streptobacilli
mycobacteria

Question 4

what are the 3 curved forms of bacteria?

Answer 4

vibrio (curved rod)
spirilla (coil)
spirochete (spiral)

Question 5

conditions needed for bacterial growth

Answer 5

• glucose nutrient
• nitrogen nutrient
• temperature
• pH
• oxygen

Question 6

why does bacteria need glucose to grow?

Answer 6

energy source for respiration (can be on the agar)

Question 7

why does bacteria need nirtoeg to grow?

Answer 7

synthesis of amino acids

Question 8

what do obligate aerobes need?

Answer 8

O2 for metabolism

Question 9

how do facultative anaerobes grow?

Answer 9

some grow best with )2 but can grow without

Question 10

how do obligate anaerobes grow?

Answer 10

grow in absence of oxygen

Question 11

what is the condition for growth (temp) for mesophiles?

Answer 11

20-40C - bacteria growth in labs are normally mesophiles

Question 12

what is the condition for growth (temp) for thermophiles?

Answer 12

40C +

Question 13

what is the condition for growth (temp) for psychrophiles?

Answer 13

below 20C

Question 14

what is direct cell count? (equation)

Answer 14

total cell count = count living + dead cells using a haemocytometer

Question 15

what are viable cell counts?

Answer 15

counting only living cells

Question 16

how is viable cell counting done?

Answer 16

a known volume of organism is added to agar plates, incubated and colonies counted

Question 17

what is the assumption when doing direct cell counts?

Answer 17

that 1 cell gives rise to 1 colony

Question 18

what is the limitation of direct cell counts?

Answer 18

makes no allowance for clumping f cells which can cause an underestimation of numbers

Question 19

what can lead to an overestimate of numbers?

Answer 19

choosing a plate with too few colonies will not give a reliable estimate

Question 20

what can lead to and underestimate of numbers?

Answer 20

some plates have too many to count reliability

Question 21

what = population in 1cm3 of original culture?

Answer 21

number of colonies x dilution factor

Question 22

what do indirect cell counts measure?

Answer 22

turbidity

Question 23

what does measuring turbidity estimate?
what is the number of microbes compared with?

Answer 23

microbe numbers by measuring cloudiness
cloudier = more microbes
compared with known standards

Question 24

what does the gram stain reaction distinguish between?

Answer 24

the 2 chemically different types of cell walls found in bacteria

Question 25

features of Gram Positive bacteria

Answer 25

- thick peptidoglycan (murein) cell wall - no lipopolysaccharide layer - stains purple - e.g. Bacillus, Staphylococcus, Streptococcus

Question 26

features of Gram Negative bacteria

Answer 26

- more complex cell wall - outer lipopolysaccharide layer - peptidoglycan (murein) cell wall - can't absorb crystal violet stain - stains red with a counterstain - e.g. Salmonella, E. coli

Question 27

what is the lipopolysaccharide layer?

Answer 27

acts as an endotoxin which protects the peptidoglycan cell wall from attack by some antibiotics and the enzyme lysozyme

Question 28

what are aseptic techniques?

Answer 28

handling cultures in such a way as to prevent contamination from unwanted organisms

Question 29

what are some aseptic techniques?

Answer 29

- sterilise work surface before and after - pass insulating loop through flame - lift Petri dish only enough to allow loop to enter and open away from mouth - secure lid with 2 pieces of tape