Microbial Growth

Question 1

What are some factors that affect microbial growth ?

Answer 1

• temperature
  -pH
• moisture content

Question 2

What is the optimum pH for most microorganism ?

Answer 2

pH 7 –? neutrophilic

Question 3

What are some examples of environmental stress conditions ?

Answer 3

• desiccation
• temp
• pH
• lack of nutrients

Question 4

What are some examples of microbial survival structures ?

Answer 4

• spores in bacteria & fungi
• cysts in bacteria
• sclerotia in fungi

Question 5

Describe Fungal Spores

Answer 5

• for survival or dispersal
• 2 types = sexual & asexual

Question 6

Describe Sexual Fungal Spores

Answer 6

• thick-walled
• resistant to unfavourable environment condition

Question 7

Describe Asexual Sexual Spores

Answer 7

• produced in very large numbers for dispersal
• low resistance to unfavourable conditions

Question 8

Describe Bacterial Spores (endospores)

Answer 8

• endospores are the most resistant life forms
• can withstand temps above boiling point & extreme desiccation

Question 9

Define vegetative cells

Answer 9

= growing cells

Question 10

Describe Bacterial Cysts

Answer 10

• modified vegetative cell
• rod shaped vegetative cell become rounded & develops a thick, chemically & physically resistant cell wall

Question 11

Define Autotrophs

Answer 11

• light/oxidation or inorganic compounds

Question 12

What are the nutritional requirements for microbial growth ?

Answer 12

• C, H, O, N, S, P
• other elements in small amounts
• also vitamins - B1 & B2

Question 13

Describe carbon sources for microbial growth

Answer 13

• maltose, sucrose & starch = good source of carbon for most micro-organisms
• celllose = slowly hydrolysed by some bacteria & many higher fungi

Question 14

Describe Nitrogen sources for microbial growth

Answer 14

• utilise both organic & inorganic nitrogen
• inorganic = atmospheric
• organic = amino acids

Question 15

What can culture media be ?

Answer 15

non-selective, selective or differential

Question 16

Define Selective/narrow spectrum media

Answer 16

• designed to discourage the growth of all organism other than those required

Question 17

Define non-selective media/broad-specturm media

Answer 17

• designed to culture broad groups of micro-organisms

Question 18

Define differential media

Answer 18

• reagents may be incorporated that can permit immediate visual differentiation of desired bacteria
• reagents can be added after incubation to detect desired bacteria

Question 19

Describe Mannitol Salt Agar as a culture media

Answer 19

• selective & differential
• differentiates Staphylococcus species by mannitol fermentation
• S. aureus ferments & S.epidermis doesn’t

Question 20

Describe the Results of Mannitol Salt Agar

Answer 20

• Positive = yellow halos around bacterial growth meaning mannitol has been fermented
• negative = no colour change

Question 21

Describe Eosin Methylene Blue Agar as a culture media

Answer 21

• selective & differential
• selective = methylene blue & eosin inhibits gram +ve bacteria
• differential = contains lactose - allows distinction between lactose fermenters & non-fermenters

Question 22

Describe the results of Eosin Methylene Blue Agar

Answer 22

• acid as a result of lactose fermentation causes dyes to precipitate and cause a ‘green metallic sheen’
• non-fermenting enteric remain colourless

Question 24

Describe the population growth of micro-organisms

Answer 24

• growth of batch cell culture can be depicted graphically
• lag phase
• exponential/logarithmic phase - cells divide at constant intervals
• stationary phases
• death phase

Question 25

What is the generation time ?

Answer 25

time taken for cells to divide or the population to double in size = generation time