Unit 3. Assignment 1: Bacterial Growth Rates
Mediums that could be used to determine shigellosis include Btilliant Green Agar, and Triple Sugar-Iron Agar. Expected results in a confirmed case of shigellosis are as follows: Brilliant Green Agar – Isolated Shigella colonies which do not ferment lactose or sucrose and appear red or white in color with no growth to trace growth on the Agar plate will be present. Triple Sugar-Iron Agar – Presence of Shigella will manifest as a red slant with a yellow butt with no H2S present. In Brilliant Green Agar, E. coli O157 would present as isolated yellow to greenish colonies surrounded by yellow-green zones. In the Triple Sugar-Iron Agar, E. coli O157 will manifest as a red slant, red butt indicating no change and no sugar fermented. These growth results and their marked differences would allow for distinguishing between E. coli and shigellosis (Black, 2012). 2.
To separate a mixed culture of S. aureus, S. epidermidis, and P. aeruginosa into three pure cultures, the following procedure should be used: a)
Make an isolation plate by diluting the mixed culture until the individual organisms become separated or far enough apart on the agar surface to be distinguished. This will form visible colonies of each organism which will be isolated from the other colonies present. b)
Flame the inoculation loop before each transfer to avoid contamination. c)
Using the inoculation loop, aseptically “pick off” the individual colonies on the isolation plate and transfer to new sterile medium. Perform this step for each of the three colonies being isolated, taking care to flame the inoculating loop between each transfer. d)
Incubate the isolated culture plates which will cause all organisms in the new culture to be descendants of the same organism, therefore providing 3 pure cultures, each of which will contain one of the organisms listed above. This procedure can be done by utilizing the streak plate method of isolation or the...
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