The Effect of Environmental Factors Such as Temperature, Osmotic Pressure, Oxygen Concentration and Ph on Microbial Growth and Survival

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The effect of environmental factors such as temperature, osmotic pressure, oxygen concentration and pH on microbial growth and survival

Microbial growth can be affected by different environmental factors such as temperature, osmotic pressure, oxygen concentration and pH. Six experiments were carried out in this report testing for microbial growth against different environmental factors. Good aseptic techniques were used to prevent contamination, resulting in a uniform set of results that are in line with the literature.

Bacteria vary greatly in terms of their characteristics and morphology. Colonies can be classified according to their colour, form, elevation, margin and size. Pure cultures of microorganisms are those that are uniform and are of the same descendants of the same organism. The isolation of colonies by streak plate technique allows the obtainment of pure cultures which can be studied further. Good quality aseptic technique and proper sterilisation are a required to ensure that all samples produced are free from unwanted organisms that can lead to contamination of microbial cultures.

Environmental factors such as temperature, osmotic pressure, oxygen concentration and pH can affect both the growth and survival of microorganisms. Microorganisms are versatile enough to adapt to different environments that they occupy that would otherwise threaten the survival of other species.

The method of isolating pure cultures of microorganisms on to a solid media was developed by Robert Koch in 1883. He added a solidifying agent to a liquid nutrient broth which supports the growth of a wide variety of microorganisms whilst the agar function is the solid media onto which the bacteria can be isolated as independent colonies which are representatives of different bacterial species.

Controlling microbial growth is necessary in numerous situations and is greatly significant in areas such as medicine. Growth of microorganisms is inhibited by either inhibiting the growth of the microorganism or killing the organism itself. This inhibition of growth involves physical or chemical agents. The process of sterilisation involves using heat, radiation or chemicals to physically eliminate cells. In particular, sterilisation allows the destruction of endospores of the bacteria. Growth is the increase in cell number and cell mass through asexual reproduction in the process called binary fission.

The aims of this report through the series of six experiments are: -Practising aseptic techniques
-Isolating bacteria from a mixed population
-Determining the optimum conditions for the growth of a range of microorganisms


Six experiments were carried out in this report to establish the effect of different environmental factors on microbial growth. The methodology is listed below.

Experiment 1: Streak plate technique to isolate individual colonies A flamed loop was used to pick up one discrete colony of Bacillus subtilis from an agar plate and streaked for single colonies onto one tryptic soy agar plate. The same procedure was then carried out from a broth culture of Micrococcus luteus onto a different tryotic soy agar plate. Both plates were then incubated at 37oC for 48 hours.

Experiment 2: Selective and differential plating
Escherichia coli, Enterobacter aerogenes and B. subtilis were each inoculated onto one EMB agar plate for single colonies that was divided into three sections. The plate was then incubated at 37oC for 48 hours.

Experiment 3: Effect of temperature on bacterial growth
Five slants were labelled with the temperatures: - 4, 25, 37, 65 and 85oC. The surface of the slants were streaked with the broth culture of E. Coli and were incubated at the appropriate temperatures for 48 hours except for the tube at -4oC which was incubated for 7 days. This procedure was repeated for broth cultures of Bacillus stearothermophilus and Pseudomonas fluroescens....
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