Please show all work
20. One-hundred grams of fresh tomatoes were placed in a stomacher and blended for 45 seconds. A 1 mL sample of blended tomatoes was placed in tube containing 9 mL of Trypticase Soy Broth, and incubated at 37C for 24 hours. After the incubation period, 1 L and 10 L loops were used to streak two separate TSA plates in order to enumerate the microbial load of tomatoes. The inoculated plates were incubated for 24 hours at 37C. After the second incubation period, a microbiologist manually counted 17 and 210 colonies, respectively. Calculate the average microbial load in fresh tomatoes. Report the microbial load as cfu/g. Show your work.© BrainMass Inc. brainmass.com October 25, 2018, 1:55 am ad1c9bdddf
This question is a good example of using a standard plate count method to determine the microbial load in fresh food. The tricky parts of this type of question are keeping track of the dilutions made and converting the volumes so that the answer is expressed using the desired units, in this case cfu (colony forming units) per gram of original food sample. I will start with a quick review of the standard plate count method then demonstrate the calculation.
In this method, a small amount of a homogenized (blended) food sample is diluted and plated onto a solid growth medium in a petri plate. After the incubation period, bacteria appear as individual colonies on the surface of the growth medium. The assumption with this method is that each colony has arisen from a single cell, an assumption that has been rightfully challenged many times, since bacteria in solution tend to aggregate. That is why we express a numerical value in colony forming units, which is likely a more accurate assumption that each colony arises from a cell or small group of cells attached to each other. Once we count the number of colonies on each plate, this can be used to calculate back to an estimate of bacteria in the original ...
Calculate the average microbial load in fresh tomatoes
Please help with the following pre-lab questions regarding protein expression in my Molecular Biology Lab
Underlying molecular principles:
Explain the genetic components of the lac operon regulating the IPTG-inducible expression of T7 RNA polymerase in the TrcHisB/T7 and DH5 system
- Inoculate and grow a transformant DH5 cell line
- Assess the cell growth phase by absorbance at 600nm
- Induce protein expression by adding IPTG
- Harvest cells from a liquid culture
- Prepare one buffer solution to be used in a future laboratory class
I need help on the following two questions:
1. Perform a quick review of literature on recombinant protein expression in E. coli and indicate the protein yield reported in two research articles of your choice. Make sure you specify the units for the protein yield. For each article describe the nature of the protein that was overexpressed (membrane protein, cytosolic protein, ...). Estimate how much of your recombinant T7 RNA polymerase enzyme you might expect from 50ml of liquid culture by assuming a yield comparable to the ones reported in the two articles you selected. A hard copy of each of your two articles along with your answer should be handed in to your TA when entering the lab
2. 2. The overview figure provided in Experiment A shows the planning for the control aliquots to be assessed by SDS-PAGE in lab 6. Due to space limitation in the shaking incubator, some controls will be done collectively. Explain the information to be obtained from each of the two extra sets of controls to be done collectively:
a. The inoculated 50ml culture containing 200ug/ml ampicillin is to be divided in two fractions of 25ml. At time zero of the induction, the first 25ml fraction is to be induced with 1mM IPTG whereas only water is to be added to the second 25ml fraction. A 1ml aliquot is to be withdrawn from each of the two fractions at both time zero and after a 1.5 hr incubation. ( /2.5 MARKS)
b. A liquid culture of non transformed DH5 cells will be incubated without ampicillin, and a 1ml aliquot is to be collected at time zero and the very end of the induction treatment with IPTG.
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