As shown in the illustration below, it begins when 1 ml of the bacterial sample is added to 9 ml, and it is mixed together creating a 101 dilution. Topics you will need to know in order to pass the quiz include dilution blank and final. A serial dilution is any dilution in which the concentration decreases by the same factor in each successive step in serial dilutions, you multiply the dilution factors for each step. If no colonies are found on the lowest dilution media plate, then move onto the second lowest dilution. This quiz and attached worksheet will help gauge your understanding of the properties of serial dilution.
In direct microscopic counts cell counting using haemocytometer where all cells, dead and living are counted but cfu measures only viable cells. Colony forming unit cfu or cfu is a measure of viable bacterial or fungal cells. Sample math problems for microbiology david fankhauser. How colony forming units are counted on microbial plate. Sample math problems for microbiology calculate the cfu100 ml in the original culture.
To make a dilution series, use the following formulas. An easy learning guide dilutions are useful in science when making solutions or growing an acceptable number of bacterial colonies to count. Since c is a 100x dilution of b, b contains 20,000 2x10e4 colonies ml. From the original culture 1 ml of broth was transferred to flask a which contains 99 ml of sterile water. Start studying serial dilution and the standard plate count. The answers i sure hope you tried to answer the problems before you looked here. Impact of dilution on microbial community structure and. The easiest method is to make a series of 1 in 10 dilutions. For the love of physics walter lewin may 16, 2011 duration. The exercise will allow students to learn how to pipette, dilute samples and calculate the concentration of their samples. To determine the concentration you multiply the number of colonies by the inverse of the dilution factor in flask b it was 104. How to work microbiology dilution problems sciencing. Now you only have to look up how many ml in 10oz and you have your answer.
Observe all the dishes that were used in this experiment. The following problem sets test your ability to calculate dilution factors and concentration s. Serial dilution is a process through which the concentration of an organism, bacteria in this example, is systematically reduced through successive resuspension in fixed volumes of liquid diluent. Divide the cfu from the dilution 179 by the result from step 1 0. The following protocol is a stepbystep procedure to working dilution problems, and includes some practice problems at the end.
Answers serial dilutions practice worksheet biol 307. A serial dilution is a series of sequential dilutions used to reduce a dense culture of cells to a more usable concentration. Since each colony on an agar plate theoretically grew from a. Moore, in current laboratory techniques in rabies diagnosis, research and prevention, volume 2, 2015. This type of dilution series is referred to as a serial dilution. This is repeated with third dilution giving another 1100 dilution. To this end, serial dilution and plating techniques are typically employed to reliably quantify bacterial load and isolate individual colonies.
A dilution series is a succession of step dilutions, each with the same dilution factor, where the diluted material of the previous step is used to make the subsequent dilution. Serial dilution is the simplest approach where cells are serially diluted to approximately one cell per microliter yuan et al. The following is a stepbystep procedure to working dilution problems, and includes some practice problems at the end. It is a common practice to determine bacterial counts for both liquid and solid specimenssuspensions of e. Our designs for this experiment must maximize the probability that useful data will be obtained since these experiments are costly, labor intensive, and time consuming. Dilutions are useful in science when making solutions or growing an acceptable number of bacterial colonies to count. If the dilution factor is in the form of a fraction, you can flip the fraction i.
Serial dilutions practice problems san diego miramar college. Working dilution problems it is a common practice to determine microbial counts for both liquid and solid specimenssuspensions of e. Determine how many moles of solute and liters of solvent you have for each solution you are. Serial dilution practice problem set science primer. If students are not familiar with operating pipettes, the pre lab serial dilutions practice exercise is recommended. To solve type two problems, simply rearrange the formula above to. Bacterial dilutions and a foolproof way to figure them out. How many cfus are there per ml in the original sample. The number of colonies that grew is indicated on the petri plates. C, is poured into a petri dish containing a specified amount of. The purpose can be determination of bacterial, fungal, or viral counts indirectly. Serial dilution and the standard plate count flashcards. Serial dilutions austin community college district.
Statistical design for a small serial dilution series. In each of the dilutions you will be performing in this lab, 0. My video will introduce the steps of diluting a bacterial culture with the goal of determining how many live bacteria are present in that culture. As it would usually be impossible to actually count the number of microorganisms in a sample, the sample is diluted and plated to get a reasonable number of colonies to count. This method is called multiplying by the inverse of the dilution factor. Most specimens have high enough numbers of microorganisms that the specimen has to be serially diluted to quantitate effectively. Dilution worksheet and problems biology libretexts. How many pipettes should be used for this dilution. A serial dilution is the dilution of a sample, in 10fold dilutions. Below is an applet to practice finding dilution factors, and also to determine how much water to add to achieve a given dilution.
Serial dilutions practice problems refer to the below image. Prepare the dilution of the test sample expected to contain between 30300 cfuml. Serial dilutions of samples are made using emem10 as the diluent in 8well labtek. Then 1 ml from flask a is transferred to flask b and then 1 ml from flask b is transferred to flask c. Serial dilutions are used to calculate the concentration of microorganisms. After retrieving your groups petri dish, sketch the appearance of the colonies in the space below. In a serial dilution, aliquots of some solution are diluted stepwise such that the first dilution serves as the source from which an aliquot is taken for the second dilution, etc. The total dilution factor is used to compare the concentrations of dilution tubes to the original culture tube. There are three formulas used to work microbiology dilution problems.
Most specimens have high enough numbers of microorganisms that the specimen has to be serially. If one ml was spread on plate a it would be x 10 4 or 000 or 1. Since a is a 10x dilution of the soup, the soup contains 2,000,000 2x10e6 colonies ml. Part 3 observation of cell colonies analysis of results. Set up the problem dilution factor final volumealiquot volume 0. Plate colonies on plate a too many to count b 685 c 52 d 4 what is the number of bacteria in the original culture. For each flask, a serial dilution of the regrown community was plated, in duplicate, onto both r2a agar and sterile sewage medium sm. Serial dilution instructions api biotechnology solutions.
If the dilution factor is in decimal form, multiply by 1 over the decimal i. Serial dilution, also called limiting dilution series, is a standard laboratory procedure employed to collect the appropriate data in order to accomplish this estimation. Determine the concentration or dilution factor for the flasks and plates. Each of the 60 colonies was inoculated onto a slant of heart infusion agar to grow cultures for gram staining and into a tube of glucose fermentation broth. Next, 1 ml of the first dilution is added to 99 ml to make the second dilution, that is a 1100 dilution. Follow serial dilution technique inoculate labeled empty petri dish with specified ml 0. When given a diagram of a plate count dilution and the number of colonies on the resulting plates, choose the correct plate for counting, determine the dilution factor of that plate, and calculate the number of cfus per ml in the original sample. Dilutions part 3 of 4 calculating colony forming unitsml.
The most common type of dilutions done in chemistry lab involve taking a sample of a solution of known volume and concentration and diluting it to some larger volume. You must do this to find the dilution factor which yielded your cfu count. The important thing to remember is that the amount of solute doesnt change during the dilution process, only the amount of solvent and. We recommend having a water analysis done so that you know what constituents and at what concentration the sample is made of.