Chapter 5 Microbial growth control Physical methods Chemical agents Food Preservation
Chapter 5 Microbial growth control Physical methods Chemical agents Food Preservation
Control of microorganisms by physical and chemical agents frequently used terms Sterilization: the process by which all living cells, viable spores, virus, and viroids are either destroyed or removed from an object or habitat Disinfection: the killing inhibition or removal of microorganisms that may cause disease Sanitization: the microbial population is reduced to levels that are considered safe by public health standards Antisepsis: the prevention of infection or sepsis cide: kill; -static: stop germicide: kill pathogens but not necessarily endospores Bactericide; fungicide; algicide; viricide; bacteriostatic fungistatic
Control of microorganisms by physical and chemical agents frequently used terms • Sterilization: the process by which all living cells, viable spores, virus, and viroids are either destroyed or removed from an object or habitat. • Disinfection: the killing, inhibition, or removal of microorganisms that may cause disease. • Sanitization: the microbial population is reduced to levels that are considered safe by public health standards. • Antisepsis: the prevention of infection or sepsis • -cide: kill; -static: stop germicide: kill pathogens but not necessarily endospores. Bactericide; fungicide; algicide; viricide; bacteriostatic; fungistatic
Conditions influencing the effectiveness of antimicrobial agent activity 1. Population size 2. Population composition. Spore, young/mature 3. Concentration or intensity of an antimicrobial agent 4. Duration of exposure 5. Temperature higher ·6. local environment eg. 1. Heat kill more readily at an acid ph 2. Organic matter protect microorganisms 3. Biofilm protection
Conditions influencing the effectiveness of antimicrobial agent activity • 1. Population size. • 2. Population composition. Spore, young/mature • 3. Concentration or intensity of an antimicrobial agent. • 4. Duration of exposure. • 5. Temperature. higher • 6. local environment. eg. 1. Heat kill more readily at an acid pH. 2. Organic matter protect microorganisms. 3. Biofilm protection
Microbial Growth Control Physical ways Heat sterilization (including autoclave and pasteurization) Radiation(microwaves, UV, X-rays, y-rays and electrons) Filtration(depth filter, membrane filter and nucleation track (nucleopore)filter
Microbial Growth Control • Physical ways – Heat sterilization (including autoclave and pasteurization) – Radiation (microwaves, UV, X-rays, g-rays and electrons) – Filtration (depth filter, membrane filter and nucleation track (nucleopore) filter)
Heat(terms) TDP: the lowest temperature at which a microbial suspension is killed in 10 minutes TDT: the shortest time needed to kill all organisms in a microbial suspension at a specific temperature and under defined conditions Decimal reduction time (D)or D value: the time required to kill 90% of the microorganisms or spores in a sample at a specified temperature. D121
Heat(terms) • TDP: the lowest temperature at which a microbial suspension is killed in 10 minutes. • TDT: the shortest time needed to kill all organisms in a microbial suspension at a specific temperature and under defined conditions. • Decimal reduction time (D) or D value: the time required to kill 90% of the microorganisms or spores in a sample at a specified temperature. D121
Moist heat sterilization Autoclave: a device somewhat like a fancy pI ressure cooker The air initially present is forced out the chamber is filled with saturated stream 121°Cor15 pounds 15-30min 1. All air must be flushed out of the chamber. or it will not reach 121C even though it may reach pressure of 15 pounds 2. The chamber should not be packed too tightly
Moist heat sterilization • Autoclave: a device somewhat like a fancy pressure cooker. • The air initially present is forced out the chamber is filled with saturated stream • 121oC or 15 pounds 15-30min 1. All air must be flushed out of the chamber, or it will not reach 121oC even though it may reach pressure of 15 pounds. 2. The chamber should not be packed too tightly
Pasteurization Milk, beer, and many other beverages are treated with controlled heating at temperatures well below boiling. Not sterilize, just pasteurized Past:63°C,30min HTST:72°C,15sec UHT:140-1500C,1-3sec
Pasteurization • Milk, beer, and many other beverages are treated with controlled heating at temperatures well below boiling. Not sterilize, just pasteurized. • Past : 63oC, 30min • HTST: 72oC, 15sec • UHT: 140-150oC, 1-3sec
Dry heat sterilization 160-170°C2-3h Suitable for glass petri dishes and pipettes Not suitable for heat-sensitive materials like many plastic and rubber items
Dry heat sterilization • 160-170oC 2-3h • Suitable for glass petri dishes and pipettes • Not suitable for heat-sensitive materials like many plastic and rubber items
Filtration Heat-sensitive solution Depth filters: diatomaceous; unglazed porcelain Membrane filters: membranes with pores about 0.2um in diameter are used to remove most vegetative cells. but not viruses Air: 1. Surgical masks and cotton plugs on culture vessels 2. Biological safety cabinets
Filtration • Heat-sensitive solution • Depth filters: diatomaceous; unglazed porcelain. • Membrane filters: membranes with pores about 0.2m in diameter are used to remove most vegetative cells, but not viruses. • Air: 1. Surgical masks and cotton plugs on culture vessels. 2. Biological safety cabinets
Radiation does not penetrate glass, dirt films, water and ut 1. Ultraviolet radiation: 260nm is quite lethal bu other substances uv lamps: the ceilings of rooms biological safety cabinets attention! uv lamp must be off 2. lonizing radiation: not always as effective against viruses Co60: cold sterilization for antibiotics hormones sutures
Radiation • 1. Ultraviolet radiation: 260nm is quite lethal but does not penetrate glass, dirt films, water and other substances. uv lamps: the ceilings of rooms biological safety cabinets attention! uv lamp must be off • 2 . Ionizing radiation: not always as effective against viruses. Co60: cold sterilization for antibiotics, hormones, sutures
