Microorganisms are sensitive to many physical or chemical agents. These agents are said to have a "bacteriostatic action" when they stop the growth of bacteria, and a "bactericidal action" when they kill them.
The sun, with its ultraviolet rays, is doubtless the oldest bactericidal agent, and one of the most efficient. Ultraviolet rays bring about mutations in bacteria, that is to say, changes in their genetic makeup, which prove to be deadly in most cases.
In general, bacteria are unable to develop in highly concentrated solutions of substances like sugar or salt. In such conditions, the water contained in the microorganisms is released through the cell wall in an attempt to dilute the medium outside (osmosis). The result is that the bacteria dehydrate and stop growing or die. This is what occurs when meat or fish is salted. Similarly, the presence of a large quantity of sugar in fruit jellies or jams helps to preserve them.
Heat is bacteria's mortal enemy. A temperature of 50 to 60 degrees Celsius (122 to 140 degrees Fahrenheit) for half an hour is sufficient to neutralize most bacteria, but those that can form spores require more stringent measures. It takes 20 minutes in a steam sterilizer to kill such germs. For this reason a surgeon's gown and the drapes over his patient are sterilized in such a manner.
Bacteria also are sensitive to many chemical substances. Knowledge of this can be put to good use in various ways, for example, in food preservation. The oldest and best-known chemical preservatives doubtless are alcohol and vinegar. More recently the chemical industry has created a wide variety of products acting either on bacteria or on fungi, and preventing their growth. Some of these chemical agents seem to be harmless, but unfortunately the long-term secondary effects of many of them are not known.
The sun, with its ultraviolet rays, is doubtless the oldest bactericidal agent, and one of the most efficient. Ultraviolet rays bring about mutations in bacteria, that is to say, changes in their genetic makeup, which prove to be deadly in most cases.
In general, bacteria are unable to develop in highly concentrated solutions of substances like sugar or salt. In such conditions, the water contained in the microorganisms is released through the cell wall in an attempt to dilute the medium outside (osmosis). The result is that the bacteria dehydrate and stop growing or die. This is what occurs when meat or fish is salted. Similarly, the presence of a large quantity of sugar in fruit jellies or jams helps to preserve them.
Heat is bacteria's mortal enemy. A temperature of 50 to 60 degrees Celsius (122 to 140 degrees Fahrenheit) for half an hour is sufficient to neutralize most bacteria, but those that can form spores require more stringent measures. It takes 20 minutes in a steam sterilizer to kill such germs. For this reason a surgeon's gown and the drapes over his patient are sterilized in such a manner.
Bacteria also are sensitive to many chemical substances. Knowledge of this can be put to good use in various ways, for example, in food preservation. The oldest and best-known chemical preservatives doubtless are alcohol and vinegar. More recently the chemical industry has created a wide variety of products acting either on bacteria or on fungi, and preventing their growth. Some of these chemical agents seem to be harmless, but unfortunately the long-term secondary effects of many of them are not known.
