Temperature On The Growth And Survival Of Bacteria Biology Essay

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Abstract: The aim of this experiment was to asses the growth and survival of 5 bacteria. The method involved placing each of the bacteria in water baths of various temperatures for certain periods of time, taking them out and placing them in their optimum temperatures and monitoring their growth/survival rate over the course of the week. The results obtained showed that how well the bacteria grew after they had been placed in their optimum temperatures and left for a week. From this it was concluded what the temperature class of each bacteria was.

Introduction: The objective of the experiment was to look at the growth and survival rate of 5 bacteria namely, Bacillus stearothermophilus, Escherichia coli, Enterococcus faecalis, Bacillus subtilis and Pseudomonas fluorescens. Escherichia coli, commonly referred to as E.coli is a gram negative bacterium which is rod shaped.

It is usually found in the large intestine of warm blooded animals. It is also found in foods and water. It is a facultative aerobe meaning that O2 is not necessarily required for growth but is preferred for better growth thus it is able to metabolise both aerobic and anaerobically. Every microorganism has a minimal, optimal and maximal temperature. These are known as cardinal temperatures and they tell us a lot about the nature of a microorganism. A mesophile is an organism which grows at its best in medium temperature conditions. A psychrophile on the other hand is an organism which is capable of growing in extremely cold temperatures. Thermophiles are virtually the opposite of psychrophiles. They're organisms which are capable of growing and reproducing the hot environments. The term thermophile means that it is heat loving or heat tolerant.

The temperature and pH are good indicators of the environment E.coli can be found. The fact that it has a ph of 6-7 means that it is found in mildly acidic to neutral places which explains why it is in the large intestine of mammals. The bacteria manage to survive in these various environments due to their adaptive metabolism. (Madigan, Martinko, Dunlap and Clark, 2008).

Enterococcus faecalis (E.faecalis) is a gram positive and is naturally occurring in the intestine of mammals, the soil, in plants and in water. The presence of E.faecalis and E.coli in the water is usually an indication that the water has been contaminated. It is found in similar habitats to E.coli.

Bacillus stearothermophilus (B.stearothermophilus) is also a rod shaped gram positive organism it is usually found in hot springs and the soil.

Pseudomonas fluorescens (P.fluorescens) is a gram negative rod shaped bacterium. It is usually found in cooler environments such as water. It is an obligate aerobe which means that it cannot grow in the absence of oxygen. Bacillus subtilis (B.subtilis) is also a rod shaped gram positive bacterium which is mainly found in the soil. It too is an obligate aerobe (Brooker, Widmaier, Graham and stilling, 2007).

Method: Please refer to the schedule for this.

Results:

Below are the tabulated results that were obtained from the experiment. Table 1 shows the effect of inoculating the bacteria at different temperatures had on their growth rate. Table 2 shows the results of exposing the bacteria to extreme heat conditions on their survival rate.

Temp (°C)

25

37

42

55

E.coli

+++

+++

+++

++

+++

+++

+++

+++

+++

+++

++

++

-

-

-

-

E.farcalis

+++

+++

+++

+++

+++

+++

+++

++

+++

+++

+++

+

-

-

-

-

B.subtilis

++

+++

++

++

+++

+++

+++

++

+++

+++

+++

+++

P.flourescence

++

+++

+++

-

++

-

-

++

++

-

-

-

-

-

-

-

-

-

-

-

B.steaothermophilus

-

+

-

-

-

-

+

-

+

-

++

-

+

++

+++

+

The table above shows how well the bacteria grew at different temperatures. Really strong growth is represented by +++, medium by ++, slow growth by + and no growth by -. Looking at E.coli for example it is clear that it only grows well in the region of 25-42°C anything beyond this showed absolutely no growth occurring.

Time (minutes)

E.coli

Temp (°C)

0

2

5

30

90

40

Y, N, Y

Y, Y, Y

Y, Y, Y

Y, Y, Y

Y, Y, Y

60

Y, Y, Y

Y, Y, Y

Y, Y, Y

N, N, N

N, N, N

80

N, Y, Y

N, N, N

N, N, N

N, N, N

N, N, N

100

N, N, Y

N, N, N

N, N, N

N, N, N

N, N, N

B.subtilis

40

Y, Y

Y, Y

Y, Y

Y, Y

Y, Y

60

Y, Y

Y, Y

Y, Y

Y, Y

Y, Y

80

Y, Y

Y, Y

Y, Y

Y, Y

Y, Y

100

Y, Y

Y, Y

Y, Y

Y, Y

Y, NTable 2: The effect of heat on survival of bacteria. Key: Y= growth present N= no growth

E.faecalis

40

Y

Y

Y

Y

Y

60

Y

Y

Y

Y

N

80

Y

Y

Y

N

N

100

Y

Y

Y

N

N

B.stearothermophilus

40

Y, N

Y, N

Y, N

N, N

N,N

60

Y, N

N, N

N, N

N, N

N, N

80

N, N

N, N

N, N

N, N

N, N

100

N, N

N, N

N, N

N, N

N, N

P. fluorescens

40

Y, N, Y

Y, Y, Y

Y, Y, Y

Y, Y, Y

Y, Y, Y

60

Y, Y, Y

Y, Y, Y

Y, Y, Y

N, N, N

N, N, N

80

N,Y, Y

N, N, N

N, N, N

N, N, N

N, N, N

100

N,Y,N

N, N, N

N, N, N

N, N, N

N, N, NDiscussion:

With the information that is in table 1 the nature of each bacterium can be established. E.coli showed exceptionally strong growth in the range of 25 to 42°C. These results are perfectly in line with the characteristics of a mesophile as such it is safe to assume that E.coli is a mesophile. This also explains why it is found in the human intestine. The core temperature of the human body is 36.8°C ± 0.7 which according to the literature is the optimal temperature of E.coli. The same thing goes for E.faecalis. It too is a mesophile and one of the locations where it is found is also the gastrointestinal tract. The information in table 1 coupled with the fact that it is found in the same location as E.coli means that it too has the same optimal temperature as E.coli.

B.subtilis grew throughout all the temperature ranges but grew the best in 55°C. It was however strange to see it grow in the areas of 25-37°C as it is by nature a Thermophile. The minimum temperature that is required for thermophiles to grow is approximately 42°C. B.stearothermophilus on the other hand showed a classic example of a thermophillic bacterium. It grew best at 55°C. The last bacterium in table 1 was P. Fluorescens. It grew well at 25°C but seemed to be decreasing quiet substantially at 37°C. The information on the table did not quiet fit in with the characteristics which are exerted by mesophiles. Mesophiles usually grow best at around 30-40°C however P.fluorescens' optimal temperature was around 25°C which meant that it could not be a psychrophile. It did however fit the characteristics of a psychrotroph. Psychrotrophs are organism which grow at 0°C i.e. similar to psychrophiles but, usually have an optimum temperature of 25°C whereas psychrophiles have and optimum temperature of 10-12°C (www1).

Table 2 showed the effects of exposing the bacteria to high temperatures had on their survival. Temperature is most likely the most important factor that contributes to the growth and survival of the bacteria. From the literature it can be gathered depending on the organism, exposing it to very high temperatures will kill it. In the case of E.coli this is the case. It managed to stay alive at 40°C for 90minutes. This is understandable as this is below its maximal temperature. Once it had been placed into higher temperatures for a long enough duration, it died off. This was not the case for B.subtilis. It proved to be growing throughout all temperature ranges for the full 90 minutes of the experiment. The fact that it managed to survive at temperatures as high as 100°C implies that it may be a hyperthermophile (Madigan, Martinko, Dunlap and Clark, 2008).

P. fluorescens also died off after being exposed to increased temperatures for some time. At 30 and 90 minutes, all of people who were doing the experiment reported that there were no bacteria alive at 60°C. At 2 minutes into the experiment at 80 and 100°C none of the bacteria were alive.

Most of the results obtained from the experiment seemed to be in line with the information found in the literature some weren't for example E.faecalis was still alive in almost all of the higher temperature ranges when clearly it shouldn't have been as it was is a mesophile and shouldn't grow after around 46°C. B.stearothermophilus, a thermophile was not growing in temperature ranges where it should have been. These mistakes may have been due to applied correct aseptic techniques while inoculating properly. In order to eliminate such errors the experiment could be run 2 to 3 times.

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