Assessment #3 Flashcards
Bacterial Nutrition
culture medium
a nutrient material prepared for the growth of microorganisms in a laboratory
inoculum
microbes that are introduced into a culture medium
culture
the microbes that grow and multiply in or on a culture medium
examples of criteria that a culture medium must meet
- right nutrients
- sufficient moisture
- proper pH
- suitable level of oxygen
- sterile
- proper temperature
agar
- a complex polysaccharide derived from a marine alga (agarophytes)
- a polymer of galactose and galacturonic acid
- isolated from seaweed agarocytes in the seaweed
- a solidifying agent added to the medium to create a solid medium
- it is NOT a nutrient itself
agar concentrations
- normal agar: 1.5% (weight per volume)
- eg - 15g per liter of water
- soft agar: 0.5% (weight per volume)
- often used for overlays
why can most bacteria not digest agar?
- most bacteria lack agarase, an enzyme that can digest agar
chemically-defined medium
- a medium whose exact chemical composition is known
- also known as a synthetic medium
fastidious organisms
organisms that require many growth factors
complex medium
- a medium whose exact chemical composition is basically unknown
- often made up of yeast, meat, protein, and plant extracts at various amounts
semi-defined medium
- a medium whose chemical composition is partially known
- between chemically-defined medium and complex medium
liquid medium
a complex medium in liquid form
reducing medium
- medium that contains ingredients that chemically combine with dissolved oxygen and deplete the oxygen in the culture medium
- used to grow obligate anaerobes
uses of bacterial media
- enrichment
- selective
- differential
- (selective and differential)
- maintenance
bacterial media for enrichment
- allows organisms to grow on the basis of what they prefer
- designed to increase numbers of desired microbes to detectable levels
- Winogradsky column
bacterial media for selection
- adds an inhibitory agent that will prevent some bacteria from growing while allowing others to grow
- suppresses unwanted microbes and encourages desired microbes
- eg - antibiotics, basic dyes, bismuth sulfite agar
bacterial media for differentiating
- addition of something that will differentiate (not inhibit) between microbes
- eg - milk agar, pH indicator, blood agar
bacterial media for maintaining
- used to maintain and preserve microorganisms for long-term
bacterial media for selecting and differentiating
- supresses unwanted microbes and differentiates colonies of desired microbes from each other
- eg - MSA (mannitol salt agar), EMB (eosin-methylene blue agar)
bacterial nutrition patterns
- energy source
- carbon source
- electron donor source (reducing power)