Counting the Number of Viable Bacteria - Coursework Example

Lab exercise
Counting the number of viable bacteria by colony count, an Excel program was used to make a chart after the counting.
There are various methods and technologies that are employed by various scientists to determine the number of viable bacteria in a colony. This can be achieved by the use of a spectrophotometer in measuring the populations ‘optical density, counting the micro-organisms directly using a hemocytometer, and by serial dilution of the bacteria and then plating them on a media that supports growth.
Another way of counting the number of bacteria is by counting colony-forming units and then determining the number of bacteria present in the original solution by counting. In this process, the colonies are placed on plates and then for each dilution, the number of counting units is determined by counting the units on the plates. The count should be between 30 and 800. The counted values are then recorded in a table in an Excel spreadsheet. In cases where the number of the CFUs is greater than 1000, then the value is recorded as TNTC i.e. Too Numerous to Count. In cases where the count is less than 10, the value is recorded but it is not utilized in the final calculation. The results are recorded in a table just like the one shown below
 
Dilution factor Number of bacterial colonies (CFUs) Avg
#
CFU Avg # bacteria/ml
T 1 T 2 T 3 T 4 T 5 T6 T 7 T 8 T 9
1: 10-1
1: 10-2
1: 10-3
1: 10-4
1: 10-5
1: 10-6
1: 10-7
1: 10-8
Calculating the Number of CFUs per Ml is done in Excel using the formula below
(Number of CFU^' s)/(Volume plated ×Total Dilution.)
What is the aseptic transfer and streak plate?
Aseptic transfer refers to the several techniques and procedures that are employed to establish control with the aim of minimizing pathogen contamination.
A streak plate is a technique in which the spreading of the loopful bacteria over a surface is done till the isolated cell is obtained on the surface.
The success of the sterile transfer experiment
The sterile transfer technique is used in the transformation of bacteria from one location to another. This ensures no additional bacteria contaminates the one (bacteria) in transit. Also, this technique is used to prevent bacteria from escaping and infecting the environment. The success of the sterile technique is dependent on several factors. The factors that facilitate the success of sterile transfer experiments are highlighted below;
Before the beginning of the experiment, the hands must be thoroughly washed and the surface being used be sterilized to remove any pre-existing bacteria.
All the ends of loops and all the transfer loops must be flamed. Also, caution should be taken such that the tubes are kept open only for the minimum amount of time possible. When the tubes are open, they should be inclined at 45 degrees.
All Petri dishes must be covered by lids to prevent organisms from falling onto the medium for nutrients. At the same time, the lid must be loosely covered to allow diffusion of air. Read More