Microbial Growth Flashcards
What are some factors that affect microbial growth ?
- temperature
-pH - moisture content
What is the optimum pH for most microorganism ?
pH 7 –? neutrophilic
What are some examples of environmental stress conditions ?
- desiccation
- temp
- pH
- lack of nutrients
What are some examples of microbial survival structures ?
- spores in bacteria & fungi
- cysts in bacteria
- sclerotia in fungi
Describe Fungal Spores
- for survival or dispersal
- 2 types = sexual & asexual
Describe Sexual Fungal Spores
- thick-walled
- resistant to unfavourable environment condition
Describe Asexual Sexual Spores
- produced in very large numbers for dispersal
- low resistance to unfavourable conditions
Describe Bacterial Spores (endospores)
- endospores are the most resistant life forms
- can withstand temps above boiling point & extreme desiccation
Define vegetative cells
= growing cells
Describe Bacterial Cysts
- modified vegetative cell
- rod shaped vegetative cell become rounded & develops a thick, chemically & physically resistant cell wall
Define Autotrophs
- light/oxidation or inorganic compounds
What are the nutritional requirements for microbial growth ?
- C, H, O, N, S, P
- other elements in small amounts
- also vitamins - B1 & B2
Describe carbon sources for microbial growth
- maltose, sucrose & starch = good source of carbon for most micro-organisms
- celllose = slowly hydrolysed by some bacteria & many higher fungi
Describe Nitrogen sources for microbial growth
- utilise both organic & inorganic nitrogen
- inorganic = atmospheric
- organic = amino acids
What can culture media be ?
non-selective, selective or differential
Define Selective/narrow spectrum media
- designed to discourage the growth of all organism other than those required
Define non-selective media/broad-specturm media
- designed to culture broad groups of micro-organisms
Define differential media
- reagents may be incorporated that can permit immediate visual differentiation of desired bacteria
- reagents can be added after incubation to detect desired bacteria
Describe Mannitol Salt Agar as a culture media
- selective & differential
- differentiates Staphylococcus species by mannitol fermentation
- S. aureus ferments & S.epidermis doesn’t
Describe the Results of Mannitol Salt Agar
- Positive = yellow halos around bacterial growth meaning mannitol has been fermented
- negative = no colour change
Describe Eosin Methylene Blue Agar as a culture media
- selective & differential
- selective = methylene blue & eosin inhibits gram +ve bacteria
- differential = contains lactose - allows distinction between lactose fermenters & non-fermenters
Describe the results of Eosin Methylene Blue Agar
- acid as a result of lactose fermentation causes dyes to precipitate and cause a ‘green metallic sheen’
- non-fermenting enteric remain colourless
Describe the population growth of micro-organisms
- growth of batch cell culture can be depicted graphically
- lag phase
- exponential/logarithmic phase - cells divide at constant intervals
- stationary phases
- death phase
What is the generation time ?
time taken for cells to divide or the population to double in size = generation time
