Environmental Influence on Microbial Growth

ENVIRONMENTAL INFLUENCE ON MICROBIAL GROWTH 7.2. Influence of temperature The temperature suitable for the growth of microorganisms varies greatly. The growth of microorganisms will occur very well at the optimum temperature. This optimum temperature usually corresponds to the temperature of its natural habitat, for example at 37 oC for pathogenic bacteria in animals. We can differentiate microorganisms into 3 groups based on their optimum growth temperature, namely: a. Psychrophilic: microorganisms that live at low temperatures (5 - 30oC). b. Mesophilic: microorganisms that live at moderate temperatures (25 - 40oC). c. Thermophilic: microorganisms that live at high temperatures (45 - 65oC) Notes: The temperature range above is not strict like that, because there are several microbes that can live in a very wide temperature range, so there is a lot of overlapping. Tools and materials a. Nutrient broth medium equipped with a Durham tube. b. CultureE. coli, Pseudomonas sp., AndSarcina lutea. c. Incubator. Ways of workin a. Plant the above cultures in nutrient broth medium. b. Incubate at temperature 5oC, 20oC, 40oC, and 65oC. c. Observe the growth after 2-7 days. 7.3. Effect of pH As with temperature, the growth of microorganisms is also greatly influenced by the pH of the environment. Tools and materials a. Nutrient broth medium with different pH (3, 5, 7, and 9). b. CultureE. coli, Staphylococcus aureus, AndS. cerevisiae. Ways of working a. Plant each culture in a medium with a different pH. b. Incubate at 30oC. c. After 2 and 7 days, observe the growth of each culture. 7.4. Influence of light Microorganisms respond well to light (some positive and some negative). Even germination is affected by light. 5.3.1 Tools and materials a. Medium NA is upright b. Sterile petri dishes c. CultureE. coliin suspension form (24 hour shelf life). Ways of working a. Pipette 1 ml of the culture suspension and place it in a petri dish. b. Melt the NA medium in a water bath, and after reaching a temperature of 40oC, put it in a petri dish containing the culture suspension. c. Shake it evenly, and let it freeze. d. Treatment of the culture was as follows: The first cup was illuminated with sunlight for 15 -30 minutes, the second cup was illuminated with lamp light for 15-30 minutes then wrapped in black paper, and the third cup was not exposed to light and was immediately covered with black paper. e. Incubate the three petri dishes at 37oC f. Observe the growth of the culture in the three petri dishes. 5.3.2Tools and materials a. One large test tube. b. Distilled water c. Filter paper d. Black paper e. Horse manure Ways of working a. Fill the test tube with distilled water to a height of 10 cm. b. Insert the filter paper so that the edge is submerged at the surface of the water c. Place the horse manure on the surface of the filter paper. d. Cover the test tube with black paper, then make a hole in the paper just above the surface of the horse manure, with a hole size of around 5 x 5 mm. e. Incubate at room temperature in a place exposed to sunlight. f. Observe the growth of mold in horse manure and note which direction it grows