The Effects Of Various Factors On The Growth Rate Of E Coli

The Effects Of Various Factors On The Growth Rate Of E. Coli The Effects of Various Factors on the Growth Rate of E. coli Introduction: There are times in our lives (as human beings) when people do not feel well. A doctor might diagnose them with a disease or an infection. There are also times when people do not feel clean.

This could be a person’s feeling after exercising, sweating, or maybe he/she had not taken a shower in a couple days. In any of the preceding scenarios, bacteria most likely played a major role in initiating a person’s feeling of illness or squalor. Sickness can be caused from bacteria. Someone may be sick because they ate food contaminated with bacteria or they could have easily taken a sip from the cup of a friend and shared some sort of bacterial disease. Bacteria surrounds us everyday, every second.

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It is difficult for people to accept this fact because they want to believe they are clean, after they shower. In relative terms, a washed person is clean, but they are not free of bacteria. Clean is simply an image, because bacteria are covering all substances and objects that you use to be clean; toothbrushes, soap, and even toilet paper. We live in a world of bacteria, maybe even a world that evolved from bacteria. These microscopic organisms reproduce quickly, sometimes even exponentially. In the experiment today, my class is observing and measuring data of how different factors can influence the rate at which bacteria grows.

We will use Escherichia coli (E. coli) as our bacteria. It is a Gram-negative bacterium that resides in the intestines of humans (Laboratory Experiences, 34). Before you can fully understand the experiment and it purpose, it is important to understand the phases bacteria go through when reproducing in various media. In general, a bacterial will go through four distinct phases; a lag phase, log phase, stationary phase, and a death phase.

The lag phase shows how bacteria reproduce at a very slow rate at first. At this point, the cells are preparing for division. They are making sure to manufacture fats and proteins for the reproduction ahead. The second phase is the log (logarithmic or exponential) phase. The bacteria is now replicating rapidly and becoming so large in numbers that space is growing smaller, as is non-hazardous room and nutrient. Due to this rapid growth, the next step is the stationary phase.

In this phase, about fifty percent of the new bacteria population will become inactive, and the other fifty percent will remain and continue replication (binary fission). The last stage of bacteria generational grow is the death stage. In the death stage, there is not enough nutrients for the entire population. This causes the death rate of E. coli to increase, and the division will slow as well.

At some point, the birth rate will be lower than the death rate, and this is displayed in the graph at the leveling off, or downward slope. From this growth curve that bacteria produces, the mean generation time (MGT) can be calculated. This will be shown later in the results section of this report. Various types of abiotic, non-living chemical and physical factors (Biology, 1027), factors try to decide which will act as catalysts and which will limit the growth of the E. coli.

There are many factors that could have an effect on the growth rate of bacteria, but we are only concerned withthree; aeration, temperature, and nutrients. The conditions for optimal growth-temperature, pH, salt concentrations, nutrient sources and so on- vary according to species. Refrigeration retards food spoilage because most microorganisms grow only very slowly at such low temperatures (Campbell, 507). Temperature acts as a catalyst for many things, and it helps speed up many chemical processes. It is stated in the lab manual ( 35) that 37 degrees Celsius is the optimal condition for E.

coli and that E. coli has a doubling time of about 20 minutes at this temperature. From this information, I predict that the higher the temperature, the higher the MGT. Our next variable that we are testing is the effect of different nutrients on E. coli.

Our first type of media to test is MSG. MSG encourages growth and also contains glucose, a supplier of carbon. The second type of media used is MSGT, which has everything that MSG has, and a new chemical called tryptose. MSGT not only has carbon, but also has nitrogen, from the tryptose. The last variable that will be using is MSGTYE. It has everything that MSG contains, everything that MSGT contains, and consists of a yeast extract.

I hypothesize that the MSGTYE will prove to have the fastest growing rate, and that MSG will have the slowest growth rate of the three. Nutrients (like carbon and nitrogen) have many functions for the growth of bacteria, and a yeast extract has other nutrients that could help MSGTYE have the greatest growth rate on E. coli. The last tests will be done to find out the effects of aeration on the growth of bacteria. Different types of bacteria can live in environments with oxygen, and some without.

In this lab, we will be making our conclusion based three flasks containing the E.coli. One flask will be a control flask, which will sit still and be exposed to the atmosphere. Another flask will be placed in a moving water bath. The water bath is used to mix different amounts of the atmosphere with E. coli.

The third and final flask will be a baffled flask, which will be placed in a trembling water bath. A baffled flask is irregular shaped and therefore may accept different amounts of oxygen. I predict that the baffled flask will have the greatest growth rate, and that the control flask will have the lowest growth rate because the baffled flask has a greater chance of the air reacting with the E. coli. Table 1 provides each culture condition and treatment for each category. For the experiment, we will use the spectrophotometer to measure temperature, aeration, or nutrients effects on the growth of E. coli.

The spectrophotometer works because it measures the absorbency of light in a solution. The more the population of the bacteria grows, the more light the solution will absorb, and the cloudier the solution will be. Methods: First our class split up into three groups, one to observe the effects of aeration on the growth of E-coli, one to observe the effects of temperature, and another to observe the effects of nutrients. Each group followed the directions in the procedures section of the lab manual (Laboratory Experiences, Spring 2001). Usin …


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