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, ...view middle of the document...
This procedure can be done by utilizing the streak plate method of isolation or the pour plate method of isolation. Streak plating microorganisms is the most common and widely accepted method used for obtaining pure cultures of bacterial colonies (Pollack, Findlay, Mondscheim, & Modesto, 2012).
3. These results suggest that the K. brevis counts are significantly increasing by more than quadrupling in number over a three day time frame, which is indicative of an impending harmful algal bloom. With this rate of increase, it is safe to speculate that a full algal bloom will occur in approximately 2.5 more days. There are other methods that may be used to investigate growth rates of bacteria, and these include filtration, measuring turbidity with a colorimeter or spectrophotometer, and using the most probable number method (Reikowski, 2013).
4. When beginning a culture of S. pneumonia with one cell at 9 a.m., the amount of cells that will be present by noon is equal to 64 cells. If you were to begin this experiment by 6:30 p.m., 20 generations will have passed (60 minutes x 10 hours = 600. 600 / 20 generations = 30 minute generation time.) If this culture is left indefinitely, logarithmic growth will only be maintained for a limited time. This is a result of the increase in the number of organisms and a decrease in nutrients, accumulation of metabolic waste, limited living space, and oxygen depletion. Limiting factor for logarithmic growth is the rate of which energy can be produced in the form of ATP. As nutrient availability decreases, cells are less able to generate ATP and their growth rate significantly decreases. This decreased growth rate results in a leveling off of the growth curve which is followed by the stationary phase unless fresh medium is introduced or the organisms are transferred to a fresh medium (Kaiser,...