Bacterial Growth Rates

879 words 4 pages
Unit 3. Assignment 1: Bacterial Growth Rates
1. 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
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5. In my opinion, using a 1:10,000 dilution factor is best to perform this plate count. This allows for a very clear picture of the colonies to be counted. When doing so, the findings are as follows:
This year – 13 colonies counted.
Last year – 3 colonies counted.
This year – 130,000 organisms per ml present.
Last year – 30,000 organisms per ml present.
These findings suggest potential variances in the ph levels of the water as well as possible variations and changes in water temperature, oxygen levels, hydrostatic pressure, and/or osmotic pressure. The findings also suggest a potential change in the nutrient components of the water which has allowed specific types of bacteria to flourish. These can all be a result of improper aeration in the water and the presence of decaying debris such as plants, fish, and other organic matter. Many of these decaying components are usually digested by aerobic bacteria. When water becomes stagnant however, the water temperature is affected causing water warmed by the sun to remain at the surface while cooler, denser water stays at the bottom where it receives no oxygen. Inorganic matter then sinks to the bottom where the only breakdown and digestion that occurs is done by anaerobic bacteria which are slower at breaking down these materials and produce foul smelling odors as a byproduct. These odors can include rotten-egg like hydrogen


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