Culture Flashcards
What is subculturing?
Transferring micro organisms from one culture to another in pure form
What are two ways to preform initial cultures and subcultures?
-streak plates
-spread plates
What are spread plates used for?
1- counting microorganisms in a liquid sample (CFU/ml)
2- sampling an environmental surface
What is defined media?
Precise chemical composition eg-glucose
What is complex media?
Digests of chemically undefined substances
What is cultural media?
Can be selective/non selective or differential
What is non-selective media designed for?
To culture broad groups of micro-organisms
What 2 ways is differential media designed by?
(1) reagents may be incorporated into the media that permit immediate visual differention of the desired bacteria
(2) alternatively reagents may be added after incubation to detect the desired bacteria
What does a “yellow halo” around bacterial growth mean?
Mannitol has been fermented and acid end products have been produced (s.aures)
What does a negative result conclude?
No colour change
No growth
(S.epidermidis)
What does large amounts of lactose fermentation cause?
The dyes to precipitate on the colony surface, producing a black centre or “green metallic sheen” (E.coli)
What does a smaller amount of acid production lead to?
Pink colouration of the growth (E.aerogenes)
What colour do non-fermenting enterics go?
Colourless (p. Vulgaris)
Describe viable counts in counting bacteria;
-> growth of bacteria from a suspension onto plates
-> a single bacterium grows to produce a visible colony
-> count colonies and extrapolate back to original suspension
How is bacterial growth defined?
As orderly increase in all major constitutes of an organism
