Control of Microbial Growth

• Sepsis (decay or putrid) - indicates bacterial contamination
• Asepsis (absence of significant contamination)
• Aseptic surgery techniques prevent microbial contamination of wounds
• Degerming: removal of microbes from a limited area (such as swabbing with alcohol-doesn't kill bacteria-only removes)
• Sanitization: lower microbial counts on eating utensils (does not completely get rid of organisms)
• Bacteriostasis: inhibiting, not killing, microbes
• Chemical control agents damage the plasma membrane by altering its permeability causing content to leak
• Damage to proteins by denaturation, chemicals & heating
• Damage to nucleic acids by heat, radiation, chemicals
• Heat- kills microorganisms
• MOIST HEAT - kill microbes by denaturing enzymes (coagulation of proteins): boiling at 100°C kills viruses within 10 minutes
• Autoclave - steam under pressure (most effective method of moist heat sterilization)
• PASTEURIZATION - mild heating sufficient to kill organisms (eliminate pathogenic microbes)
• 72°C for 15 mins - high temp
• 140 degree for <1 sec [can be stored in the fridge] - ultra high temp
• Pasteurization reduces spoilage organisms and pathogens (different milk products require different temp and time)
• For milk, the industry uses the phosphatase test
• Dry Heat kills by oxidation
• Dry Heat - flaming (loops)
• Dry heat - incineration (paper, bags, dressings)
• Dry heat - hot-air sterilization (surgical instruments)
• Thermal death point: lowest temp at which all cells in a culture are killed in 10 mins
• Thermal death time : time to kill all cells in a culture
• Decimal reduction time: minutes to kill 90% of a population at a given temp
• High pressure denatures proteins
• Desiccation prevents metabolism
• Osmotic pressure causes plasmolysis
• Dessication - absence of water (microrganism's growth and reproduction is halted)
• Lypophilization - also known as freeze-drying
• Hypertonic environment draws water out of the cell thru OSMOSIS that kills the microbes
• Yeast and Mold more capable than bacteria to withstand low moisture and high osmotic pressure environment
• Dessication - disruption of metabolism (nvolves removing water from microbes, primarily bacteriostatic)
• Ionizing Radiation - gamma rays, x-rays, high energy electron beams
• lonization of water forming highly active HYDROXYL RADICALS (kills microbes)
• Ionizing Radiation - for sterilization of pharmaceuticals and disposable dental and medical supplies
• Ionizing Radiation - for protection against bioterrorism (sterilizes mails)
• Non-Ionizing Radiation - longer wavelength than ionizing radiation
• UV light - damages the DNS of exposed cell (causing bonds to form between pyrimidine bases usually thymines in DNA )
• Thymine - inhibit correct replication of DNA
• Microwave - kill but do not have much effect on microbes