Scientists use a number of different methods to determine the nu mber of micro- organisms that are present in a given population. This can be accomplished by usi ng the spectrophotometer to measure the optical density of the population, by directly counting the microorganisms using a haemocytometer, or by serial diluting the bacteria and plating the diluted bacteria on media t hat supports the growth of the micro-organisms. The latter method is somewhat more time consuming, but provides statistically accurate and repeatable results. This method is also the ideal method for enumerati ng microorganisms in a given population because it only identifies the living organisms in that population.

OVER 25 years ago, I began to treat allergic otolaryngologic problems, using several techniques. Well over a decade ago, I became interested in Rinkel's method of serial dilution antigen titration for inhalant allergies because of the superior results obtained by colleagues using this method. For the past 12 years, I have.

Microbial counting is useful in the basic sciences a nd is used determine the number of bacteria present for physiol ogical or biochemical studies. For example, if one knows t he number of bacteria present in a culture then one can calculate the amount of protein or DNA that can be isolated from t hat population. Microbial enumeration is al so routinely used in the areas of public health. Food or water micr obiologists test food, mi lk or water for the numbers of microbial pathogens to determine if these products are safe for human consumption. We will be using serial dilutions, plating and counting of live bacteria to determine the number of bacteria in a given population. To this end we wil l make serial diluti ons of a solution containing an unknown number of bacteria, plate these bacteria and determine the total number of bacteria in the original solution by counting the number of colony forming units and comparing them to the di lution factor. Each colony forming unit represent s a bacterium that was present i n the diluted sample.

The numbers of colony for ming units (CFU’s) are divided by the product of the dilution factor and the volume of the plated diluted suspension to determine the number of bacteria per mL that were present in the original solution. Homer Simpson Doh Sound Download Free there. Students should obtain 10 small, sterile test tubes, label the tubes 1 through 10 and then add 4.5 mL of M9 salt s to each test tube. M9 salts is a physiological buffered mini mal medium that contains inorganic salt s but no carbon source. Bacteria will not grow in this media but will remain in a state of stasis until the diluted cells are plated on media containing a carbon source.

The students should pipette 0.5 mL of the original solut ion into test tube 1. This bacterial suspension should be mixed thoroughly (using the vortexers on each bench) before proceeding to the next step. The students should obtain a cl ean pipette and withdraw 0.5 mL of the diluted bacterial suspension from the first test tube and pipette that into the second test tube. Continue in this fashion unti l you have serially diluted the original bacterial suspension into test tube 7. The instructor will show you how to perform this exercise. In test tube 1 you have diluted the bacteria 10 fold, a 1:10 or 1 x 10.

Of the diluted suspension from the appropriately diluted test tube onto the surface of the plate. Dip the hockey stick into the alcohol solution and flame t he stick until the alcohol has burned off. Do not heat the stick to l ong; you only need to flam e the loop to burn off t he alcohol—that will be sufficient for steri lizing the hockey stick. After sterilizing the stick, use the hockey stick to spread the bacterial suspension evenly over the entire surface o f the plate. Allow the plate to dry. Continue this process wit h the remainder of the bacter ial dilutions. Wordpress Easy Media Gallery Pro Free Download on this page. Tape all of your plates together and incubate your plates, upside down, at 37.