Control of microbes——【产业与普通微生物学】
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2. Moist heat utilizes steam under pressure The latter is more effective. Water has a very
high heat capacity (ability to carry heat) and moist air is capable of holding more heat than dry air. Moist heat is therefore more effective because it increases the rate of heat penetration into a substance.
• With dry heat a higher temperature or longer time of exposure is necessary to obtain the same amount of killing as that seen with moist heat.
The goal of a heat treatment is • to bring the target population down to some acceptable level. Each species of microbe also has its own characteristic resistance to heat, with some bacteria being much more heat tolerant than others.
Control of
microbiபைடு நூலகம்l growth
The object of microbial control can range from complete eradication of microorganisms to the mere inhibition of their growth.
Types of heat treatments
1. Incineration（焚烧）.
This typically destroys all living things as well as the sample that contains them. Incineration was used in the past to prevent the spread of infectious disease.
Selective removal of a subset of microbes.
In many cases only certain microbes are damaging to an item and more gentle treatments can be used to eliminate only these harmful microbes without killing everything. A good example of this is heat treatment of milk. Treatment of milk at 72°C for 15 seconds (or 66°C for 30 minutes), termed pasteurization, will kill common pathogens transmitted in milk, including tuberculosis bacilli, E. coli and Salmonella enterica strains. While many harmless bacteria are not killed by this treatment, their elimination it is not necessary.
Physical methods 1. Temperature
High Temperature
High temperature kills by causing lysis of the membrane or denaturation of critical enzymes.
1. Dry heat involves incubation in an oven-like environment
Sterilization is the complete removal of all life forms from a given area (note that this includes viruses even though they are not really living).
Items that need to be sterile before use include medical instruments, syringes(注射器), bandages, fermentation vessels, culture media, and some kinds of food. Contamination of these items with any type of organism would be deleterious, either causing infection or unreliable research results.
A final factor influencing the effectiveness of a heat treatment is the composition of the environment surrounding the microbe. High salt and acidic environments increase the rate of killing at a given temperature due to the damaging effects salt and acid have on the cell.
high heat capacity (ability to carry heat) and moist air is capable of holding more heat than dry air. Moist heat is therefore more effective because it increases the rate of heat penetration into a substance.
• With dry heat a higher temperature or longer time of exposure is necessary to obtain the same amount of killing as that seen with moist heat.
The goal of a heat treatment is • to bring the target population down to some acceptable level. Each species of microbe also has its own characteristic resistance to heat, with some bacteria being much more heat tolerant than others.
Control of
microbiபைடு நூலகம்l growth
The object of microbial control can range from complete eradication of microorganisms to the mere inhibition of their growth.
Types of heat treatments
1. Incineration（焚烧）.
This typically destroys all living things as well as the sample that contains them. Incineration was used in the past to prevent the spread of infectious disease.
Selective removal of a subset of microbes.
In many cases only certain microbes are damaging to an item and more gentle treatments can be used to eliminate only these harmful microbes without killing everything. A good example of this is heat treatment of milk. Treatment of milk at 72°C for 15 seconds (or 66°C for 30 minutes), termed pasteurization, will kill common pathogens transmitted in milk, including tuberculosis bacilli, E. coli and Salmonella enterica strains. While many harmless bacteria are not killed by this treatment, their elimination it is not necessary.
Physical methods 1. Temperature
High Temperature
High temperature kills by causing lysis of the membrane or denaturation of critical enzymes.
1. Dry heat involves incubation in an oven-like environment
Sterilization is the complete removal of all life forms from a given area (note that this includes viruses even though they are not really living).
Items that need to be sterile before use include medical instruments, syringes(注射器), bandages, fermentation vessels, culture media, and some kinds of food. Contamination of these items with any type of organism would be deleterious, either causing infection or unreliable research results.
A final factor influencing the effectiveness of a heat treatment is the composition of the environment surrounding the microbe. High salt and acidic environments increase the rate of killing at a given temperature due to the damaging effects salt and acid have on the cell.