Heat On Growth And Survival Of Different Bacteria Biology Essay


Five bacteria have been allocated in the form of broth cultures. The five bacteria include Escherichia coli, Pseudomonas fluorescens, Enterococcus faecalis, Bacillus subtilis and Bacillus stearothermophilus. The first experiment will study the amount of growth for these five bacteria when incubated at different temperatures. Five nutrient broths will be aseptically inoculated with a loop full of each bacterium and placed for incubation at the correct temperature.

In a separate experiment, the five bacteria will be exposed to high temperatures for set periods of time and then incubated. Five nutrient broths will be placed in each 4 water baths of different temperatures for 5 minutes. Each bottle will then be inoculated with a drop of culture and placed back in the designated water bath, each bottle will be removed from the water bath at timed intervals and this will enable the observation of the effect of heat on the survival of bacteria.

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Mesophiles generally like to grow when the temperature ranges from 10oC to 52oC; these Mesophiles are then split into groups of optimum growth. Group 1, which has a optimum growth temperature between 20-30oC and group 2, which has a optimum growth temperature between 35-45oC. (Carpenter, 1972). From the results it can be said that E. coli is a Mesophile because it was unable to grow when incubated at 5oC and 55oC however grew between the ranges of 25oC and 45oC, which specifies within the growth range of Mesophiles. The results also show that the highest amount of growth was at 37oC that would put E. coli in the second group of optimum growth temperature. (Carpenter, 1972) From table 2 its possible to see that E. coli was able to survive for a long period of time when exposed to 60oC but eventually destroyed after 30 minutes, this is why E. coli is such a problematic cause of illness in humans because the optimum growth temperature of E. coli is the same as the internal temperature in the human body. (Campbell & Reece, 2004) Table 1 shows that E. faecalis most growth was at 37oC which was moderate, this is because E. faecalis optimum growth is at 35oC (Hacker & Dobrindt, 2006) There was no growth at 5oC and 55oC which makes this bacteria a Mesophile. Table 2 shows that E. faecalis can survive exposure to high temperatures better than E. coli as it survives 2 minutes at 80oC but is soon destroyed after. This is an issue as it causes the majority of human enterococcal infections such as urinary tract and abdominal infections. (Willey et al, 2007) Psychrophiles are usually found in lakes and uncultivated soils, where growth can occur at temperatures of 0oC (Carpenter, 1972) and looking at table 1, P. fluorescens is the only bacteria in the test to grow at 5oC which suggests that it could also grow below this temperature therefore can be considered a Psychrophiles. P. fluorescens optimum growth temperature is between 25-30oC (Baron, 1996) which shows in the results as there was heavy growth at 25oC. P. fluorescens survived 2 minutes into 60oC and was destroyed thereafter, survival at this temperature can cause dairy products such as milk to spoil through the production of proteases and lipases. (Baron, 1996) Although B. subtilis shows signs of growth at 45oC its optimum growth temperature is between 30-37oC (Carpenter, 1972) and from the table its possible to see that there was heavy growth at 37oC making it a Mesophile. B. subtilis is naturally found in soil and vegetation (Campbell & Reece, 2004) therefore the bacteria needs to be able to withstand various temperature conditions. This stability can be seen in table 2 where the bacteria is able to survive 5 minutes at 100oC and is then destroyed.