The Rate of Growth on Bacteria at Different Temperatures
As we began our studies in the field of bacteria by culturing
various different strands of bacteria, I wondered if different temperatures would
effect the growth rate. Could bacteria live in extreme heat and extreme cold? Do
certain kinds of bacteria strive greater than others in the conditions? These are
the questions that were burdening me until now.
Throughout the course of my experiment, I had two trials of
dishes in five different temperatures. [I used two trials to reduce my chance of
error.] The temperatures I used in my experiment were: Refrigerator, Room
Temperature [25-27 Degrees], 30 Degrees, 37 Degrees, and 45 Degrees. All of my
bacteria was continuously incubated for the duration of my experiment. After
observation, I placed them back into incubation.
I took clean source cultures of B. Cereus, E. Coli, and
S. Marcecsens and made my experimental cultures. The cultures made were dot cultures.
These are made by sterilizing a loop, taking a sample of bacteria onto your loop,
and then merely putting a single dot onto the dish. Place several dots on the dish,
again to reduce the possibility of error. Once grown, the diameter of the bacteria
grown around the dot will be the scale I use to determine the rate of growth within
the bacteria.
The way in which I allocated my data was simply by taking the
grown cultures, finding the most circular growth[luckily all of my bacteria grew in
circles], and measured the diameter. The number represented in my data is the
average taken from two dots in both sets of cultures at the same temperature.
I also made a scale to gage the thickness of my bacteria. Later
I found this not to be valid as none of my bacteria grew thick, and only outward.
This would be a good scale to use in situations where bacteria grew on top of itself,
however for my cause it is not necessary. As noted in my journal entries, the
thickness remained constant and never showed any change.
My hypothesis is that bacteria will strive at higher temperatures
and diminish at lower temperatures. I also feel that there will be a point where the
bacteria ceases to grow in terms of heat.
My results have been divided into the three enclosed graphs.
Chart 1 is my data of B. Cereus in all the various temperatures. Chart 2 is my data
of E. Coli in all the various temperatures. Chart 3 is my data of S. Marcecsens in
all the various temperatures.[Due to limited time, I was only able to record 4 days
of observation for S. Marcecsens.] The x-axis represents the number of days that have
elapsed, and the y-axis represents the temperature the bacteria was incubated at.
The legend in the lower right hand corner of the chart indicates the corresponding
line to vial.
What my data revealed was all laid out and simple: The
refrigerated bacteria never grew. In early stages, the 37 Degree bacteria grew
fastest in all bacteria, but all dishes eventually evened out in time. The 45 Degree
bacteria ran into problems with the agar. The heat was simply too great for the
amount of agar in my dishes. The heat completely dried them out within a few days.
Growth imminently terminated.
I feel that my experiment was pretty much free of procedural
errors. My data was very consistent. All of my dishes looked identical. The growth
was astoundingly similar. However, there is one apparent trait of growth which I
found especially astounding. Growth in all cultures seemed to subdue after ~3 days
of incubation. Originally, I would have thought that the bacteria would continue
growth and eventually invade the entire agar dish. However, I have learned thus far
that the bacteria growth of these bacteria are very limited. This evidence is easily
portrayed in my graphs, as the peaks level off at about the third day.
In conclusion, It is now very apparent that bacteria grows best
at approximately 37 Degrees. The bacteria ceases to grow at about 3 days, and cannot
live in temperatures around and above 45 Degrees. If I had more time, there would be
just one last side experiment I would like to conduct: Does the refrigeration of the
bacteria merely retard growth or kill growth altogether? Bacteria never appeared for
me in any of my dishes. A simple side experiment could be arranged by simply letting
the dotted cultures, once refrigerated into room or incubated temperatures. If growth
appears, we know the cold retards the growth; if no growth appears, we know the
bacteria has been destroyed.
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