omegabio

Bacteria Population Counts DISCUSSION As part of daily routine, the laboratory microbiologist often has to determine the number of bacteria in a given sample as well as having to compare the amount of bacterial growth under various conditions. Enumeration (counting of microbes in a sample) is especially important in dairy microbiology, food microbiology, and water microbiology. Since the of microorganisms involves the use of extremely small dilutions and extremely large numbers of cells, scientific notation is routinely used in calculations. A review of exponential numbers, scientific notation, and dilutions is found in Appendix A. THE PLATE COUNT (VIABLE COUNT) The number of bacteria in a given sample is usually too great to be counted directly. However, if the sample is serially diluted (see Fig. 1) and then plated out on an agar surface in such a manner that single isolated bacteria form visible isolated colonies (see Fig.

Epa Design Manual Odor Corrosion Control Consultants. Enumeration of bacteria in a population: Using serial dilutions and plating to establish viable bacterial cell count. Serial dilution performed on blue dye solution. Notice the color gradually getting paler as dilution advances. Dilution is the act of mixing a chemical with other substance, usually distilled water to make it lighter in composition. A serial dilution is the stepwise dilution of a substance in solution. Usually the dilution factor at each step is constant, resulting in a geometric progression of the concentration in a logarithmic fashion. A ten-fold serial dilution could be 1 M, 0.1 M, 0.01 M, 0.001 M.

2), the number of colonies can be used as a measure of the number of viable (living) cells in that known dilution. However, keep in mind that if the organism normally forms multiple cell arrangements, such as chains, the colony-forming unit may consist of a chain of bacteria rather than a single bacterium. In addition, some of the bacteria may be clumped together.

Therefore, when doing the plate count technique, we generally say we are determining the number of Colony-Forming Units (CFUs) in that known dilution. By extrapolation, this number can in turn be used to calculate the number of CFUs in the original sample. FORMULAS AND INFORMATION YOU NEED TO KEEP IN MIND Total = Previous Volume Transferred Dilution Dilution New Total Volume Plate Dilution = (Dilution in the test tube) (Volume Transferred) CFUs/ml = (Number of colonies on the plate) (Dilution factor of the plate) Dilution factor = inverse of the dilution Only the plate with between 30 and 300 colonies is significant. (In other words, you only count the colonies on the plate with 30-300 colonies.) There are only 2 significant numbers. You report your results in scientific notation.

1: Plate count dilution procedure. 2: Single Isolated Colonies Obtained During the Plate Count Example: A plate containing a 1/1,000,000 (or 10 -6) dilution of the original ml of sample shows 150 colonies.

150 represents 1/1,000,000 the number of CFUs present in the original ml. Therefore the number of CFUs per ml in the original sample is found by multiplying 150 x 1,000,000 (or 10 6). In scientific notation, we would report that as 1.5 x 10 8 CFUs/ml. Recall our formula from the previous page CFUs/ml = (Number of colonies on the plate) (Dilution factor of the plate) Our plate had 150 colonies and a dilution of 10 -6.

Therefore, our dilution factor = 10 6. So, our formula would be calculated as CFUs/ml = 150 x 10 6 = 1.5 x 10 8 OUR EXPERIMENT We are going to imagine that we want to determine the bacterial population count of a Tryptic Soy broth culture of Escherichia coli. MATERIALS Culture of E.

Coli 6 test tubes each containing 9.0 ml sterile water 3 sterile Petri dishes liquid TSA cooled to 96°C,agar plates of TSA 7 sterile 5 ml pipettes pipette pump PROCEDURE 1. Aseptically dilute 1.0 ml of a sample of E. Coli as shown in Fig. 1 and described below. Remove a sterile 5.0 ml pipette (This is the 1 st pipette you will use.) from the bag.

Do not touch the portion of the pipette that will go into the tubes and do not lay the pipette down. From the tip of the pipette to the first line is 0.5 ml. The largest lines mark whole milliliters.

The medium lines mark 0.5 ml. The smallest lines mark 0. Telecharger Driver Hp Photosmart C4280 Gratuite. 1 ml.

Insert the cotton-tipped end of the pipette into a pipette pump. Insert the pipette to the bottom of the flask, and withdraw 1.0 ml of the sample by turning the pipette pump knob. Draw the sample up slowly so that it isn't accidentally drawn into the filler itself. Dispense the 1.0 ml of sample into the first test tube of 9.0 ml of sterile water either by turning the pipette pump knob or depressing the release trigger.