Exercises 5: Post-Laboratory Discussion for Sterilization
v Set-up B: Set-up A: Set-up C: Set-up D: Non-sterile medium in a Sterile Petri dish Sterile medium in a Sterile Petri dish Non-sterile medium in a Non-sterile Petri dish Sterile medium in a Non-sterile Petri dish
For Non-sterile Media: The microorganisms form mostly at the center of the medium. For Non-sterile Petri dishes: At first, the microorganisms form mostly in between the wall and the dish. Then, they spread at the surface of the medium.
Death Rate α [Microorganisms] Thermal Death Time (TDT) -time required to kill a known population of microorganisms in a specific suspension at a particular temperature. ↑ Temperature, ↓ TDT and ↓ Temperature, ↑ TDT
Significance of this experiment: In order to have a successful experiment, the medium and the Petri dish must be properly sterilized.
<ul><li>How does moist heat and dry heat sterilization eliminate microbial growth? </li></ul>Dry Heat Moist Heat Kills by protein coagulation/ denaturation of enzymes and essential proteins. There is a breakage of H-bonds that holds protein 3-D structure Kills by destructive oxidation of the essential cell constituents rather than protein coagulation
2. Explain the difference when performing sterilization in a microbiology laboratory in UP Baguio as compared to UP Manila. What necessary adjustments may be done? There is no difference. Why? We are just concern with the system inside a pressure cooker or an autoclave which is not affected by the pressure and temperature of the outside environment. We can still manage to sterilize culture media and materials in an autoclave (121 o C, 15 psi, 15 mins.) without making any adjustments.
3. Account for the differences in the microbial growth (absent or present) in the four set-ups. Set-up Surface Inner Colony (groups) nsM-sP Present Present Present sM-sP Absent Absent Absent nsM-nsP Present Present Absent sM-nsP Present Absent Present