Food Microbiology Laboratory question, **********Question********** (PLease help
ID: 208469 • Letter: F
Question
Food Microbiology Laboratory question,
**********Question********** (PLease help me to figure out the answers after reading/ using following text, thx a lot)
1. Deeply introduce how to use "3M Petrifilm E.coli/Coliform (EC) count plate" in this laboratory, and indicate what is the possible errors.
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Laboratory: Microbiological analysis of food products (3M Petrifilm E.coli/Coliform (EC) count plate)
Used media:3M Petrifilm E.coli/Coliform (EC) count plate
3M EC count plates are designed to identify both E. coli and other coliforms. It contains crystal violet and bile salt which can inhibit gram-positive bacteria. E. coli will produce blue precipitate after reacting with the glucuronidase activity indicator. Coliform bacteria will ferment lactose contained in the EC count plate and produce acid, which will turn pH indicator into red color.
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Food products used: 2 Char sui samples (Store at 4°C and room temperature for 20 hours)
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Most Probable Number (3-tube MPN)
The "most probable number" (MPN) method is a useful, if underutilized, tool for the microbiologist. The test is a method to estimate the concentration of viable microorganisms in a sample by means of replicate liquid broth growth in ten-fold dilutions and is particularly useful with samples that contain particular material that interferes with plate count enumeration methods.
For MPN test, the sample to be tested is prepared in 10-fold dilution series, and then 1mL samples of each dilution are inoculated into triplicate broth culture tubes for incubation. As the dilutions increase, the possibility that the broth tubes will fail to be inoculated with any microorganism increases. At some point therefore, very few of the replicate tubes will be inoculated with viable microorganisms.
Following incubation, all tubes are examined for turbidity and the pattern of growth in the tubes is scored against a table of such values. The MPN table from the US Food and Drug Administration's Bacterial Analytical Manual (BAM) (http://www.fda.gov) is provided above. A typical design uses three replicates with a three-log10 unit dilution series (although varying numbers of replicates and different dilution series may also be used). In this design, if all tubes showed growth, then the results will benotedas3,3,3. If only one tube in each replicate shows growth it would be denoted as 111. The pattern of growth is then read from the table to provide the most probable number and 95% confidence interval. By this, the result of 2,1,0 would reflect an MPN of 15, and a result of 3,2,2 would be interpreted as an MPN of 210.
Figures 1 and 2 show this in graphic depiction. As the incubated tubes would be read 3,2,1, the MPN would be recorded as 150. The MPN table normally only presents results for three dilutions in sequence (e.g. 10-1,10-2, 10-3), but the dilution series tested might have been from the 10-2 to 10-4 tubes. We will need to take the dilution factors in the table and in the actual experiment into account to derive the most probable number from this study.
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Procedure:
3.1 The 3M™ Petrifilm™ E.coli/Coliform Count Plate provides a confirmed result of coliform and E. coli enumeration in 24 to 48 hours. It eliminates the confirmation steps and reduces the detection time and overall lab costs.
3.2 Open the cover of the Petrifilm, pipette 1 ml 10-1 dilution and 1 ml from 10-2 dilution from both food samples, on each of a 3M Petrifilm E.coli/Coliform Count Plates. (A total of 4 Petri-films for 2 food samples)
3.3 Incubate plates at 37oC for 24h. Confirmed E. coli coliforms are blue colonies with associated gas bubbles.
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Results:
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Explanation / Answer
To count the colony number at the end of the plating we need to look fort wo thing. how many colonies are on the plate and how much the soulution was diluted before plating.
So here two different dilution, 10-1 and 10-2 were used for two plate different bacteria, E.coli and Coliform and after the end of the exepriment plates were checked and colonies were counted.
then the dilution factor are 1/10 and 1/100
now, to count the colony we just need to mutiply the number of the colony with the dilution factor.
in coliform only , 10-1 dilution give rise to 4 colonies and at 4oC only 1 colony.
no of the total colony is then 4 /1/10 or 4 X 10=40
and 1/1/10 or 1X 10= 10