10. In the laboratory, you were given a 25 gram sample of ground turkey to analy

Question

10. In the laboratory, you were given a 25 gram sample of ground turkey to analyze for lactic acid bacteria (LAB) as part of a shelf-life study. You added 225 ml of MRS diluent (used to support growth of lactics) to 25 g sample and stomached to homogenize. You made a series of three 1:10 dilutions in test tubes. You pour plated Lactobacilli MRS agar with 0.4 ml of sample from the original sample bag as well as the three successive 1:10 dilutions in the test tubes. After appropriate incubation in the anaerobe jar, the plate from the sample bag was TNTC, the plate from the first 1:10 dilution test tube was also TNTC, the plates from the second 1:10 dilution had 212 and 199 CFU, while the plates from the last 1:10 test tube dilution had 12 and 19 colonies. Which is the appropriate dilution from which to calculate the number of LAB from the ground turkey sample? Now calculate the estimated number of LAB from the original ground turkey sample and give the appropriate measurement unit (per ml, cm^2, or g).

Explanation / Answer

The appropriate dilution is last dilution because in the last dilution you will find the exact or pure colonies of LAB. So better take last dilution count.

The calculation of results are as follows:

the dilution factor for the sample is 103

CFU = no. of colonies formed X dilution factor / volume of culture plate.

= 12 X 103 / 0.4 = 3X103 /ml

= 19X103 / 0.4 = 4.7X104/ml

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