Muntinlupa Science High School
RESEARCH I
HAND OUTS
MICROBIOLOGY
Terminology of Microbial Control
1. The control of microbial growth can prevent infections and food spoilage.
2. Sterilization is the process of destroying all microbial life on an object.
3. Commercial sterilization is heat treatment of canned food s to destroy C. botillinum endospores.
4. Disinfection is the process of reducing or inhibiting microbial growth on a nonliving surface.
5. Antisepsis is the process of reducing or inhibiting microorganisms on living tissue.
6. The suffix –cide means to kill; the suffix –stat means to inhibit.
7. Sepsis is bacterial contamination.
Physical Methods of Microbial Control
Heat
1. Heat is frequently used to eliminate microorganisms.
2. Moist heat kills microbes by denaturing enzymes.
3. Thermal death point (TDP) is the lowest temperature at which all the microbes in a liquid will be killed in 10minutes.
4. Thermal death time (TDT) is the length of time required to kill a bacteria in a liquid culture at a given temperature.
5. Decimal reduction time (DRT) is the length of time in which 90% of a bacterial population will be killed at a given temperature.
6. Boiling (100°C) kills many vegetative e cells and viruses
7. Autoclaving (steam under pressure) is the most effective method of moist heat sterilization. The steam must directly contact the material to be sterilized.
8. In HTST pasteurization, a high temperature is used for short time (72°C for 15 secs) to destroy pathogens without altering the flavor of the food. Ultra high temperature (UHT) treatment (140°C for 30 secs) is us3ed to sterile dairy products.
9. Methods of dry heat sterilization include direct flaming, incerination, and hot air sterilization. Dry heat kills by oxidation.
10. Different methods that produce the same effect (reduction in microbial growth) are called equivalent treatments.
Filtration
1. Filtration is the passage of a liquid or gas through a filter with pores small enough to retain microbes.
2. Microbes can be removed from air by high-efficiency –particulate air filters.
3. Membrane filters compost of nitrocellulose or cellulose acetate are commonly used to filter out bacteria, viruses, and even large proteins.
Low Temperature
1. The effectiveness of low temperatures depends on a particular microorganism and the intensity of the application.
2. Many microbe s survive (but do not grow) at the sub zero temperatures used to store foods.
3. Most microorganisms do not reproduce at ordinary refrigerator temperatures (o-7°C).
Desiccation
1. In the absence of water, microorganisms cannot grow but can remain viable.
2. Viruses and endospores can resist desiccation.
Osmotic Pressure
1. Microorganisms in high concentrations of salts and sugars undergo plsamolysis.
2. Molds and yeast are more capable than bacteria of growing in materials with low moisture or high osmotic pressure.
Radiation
1. The effects of radiation depend on its wavelength, in tensity, and duration.
2. Ionizing radiation (gamma rays, X rays, and high energy electron beams) has a high degree of penetration and exerts its effect primarily by ionizing water and forming highly reactive hydroxyl radicals.
3. Microwaves can kill microbes indirectly as materials get hot.
4. Ultraviolet (UV) radiation a form of nonionizing radiation has a low degree of penetration and causes cell damage.
oh ayan na. For FERMI and other juniors.
