The optimum
temperature range for
bacterial growth is between 5-63℃.
This is known as the danger zone as it is dangerous for some foods to be in this temperature range for prolonged periods of time.
- Moisture – Bacteria need moisture in order to grow.
- Food – Food provides energy and nutrients for bacteria to grow.
One type of extremophiles is called thermophiles. These organisms can survive at very high temperatures. In the 1960s, heat resistant bacteria were discovered in hot springs in Yellowstone National Park.
Freezing food and holding it at temperatures below 0°F can stop bacterial growth. Temperatures at the high end of the Danger Zone, above 140°F, can also be used to prevent bacterial growth.
Most yeasts and molds are heat-sensitive and destroyed by heat treatments at temperatures of 140-160°F (60-71°C). Some molds make heat-resistant spores, however, and can survive heat treatments in pickled vegetable products.
According to their growth temperature range, bacteria are classified as: psycrophiles: cold-loving organisms, optimum growth temperature is 15°C or lower. mesophiles: include most bacteria, optimum growth temperature is 20 - 45°C. Many pathogens are mesophiles as their preferred temperature is body temperature (37ºC).
The ideal temperature for bacterial growth is between 40 and 140°F - what FSIS calls the "Danger Zone." Some bacteria can double their numbers every 20 minutes at temperatures above 40°F. In 2 hours, these bacteria can become so great in number that they may cause an illness or form toxins that cause illness.
Each type of bacteria has its own preferred conditions for growth. Under ideal conditions, many types of bacteria can double every 20 minutes. Potentially, one bacteria can multiply to more than 30,000 in five hours and to more than 16 million in eight hours.
Bacteria start to die at about 55 degrees Celsius but you need to have a core temperature of above 75 degree Celsius to be confident that most of the harmful bacteria in the food has been destroyed. Even higher temperatures are needed to destroy toxins and spores produced by some of the bacteria types.
Bacteria, single celled eukaryotes and other microbes, can only live and reproduce within a certain range of environmental conditions. As the temperature increases, molecules move faster, enzymes speed up metabolism and cells rapidly increase in size.
Temperatures below the minimum usually have a static action on microorganisms. They inhibit microbial growth by slowing down metabolism but do not necessarily kill the organism. Temperatures above the maximum usually have a cidal action, since they denature microbial enzymes and other proteins.
Bacteria can live in hotter and colder temperatures than humans, but they do best in a warm, moist, protein-rich environment that is pH neutral or low acid. There are exceptions: some bacteria thrive in extreme heat or cold. some can survive under highly acidic or extremely salty conditions.
E. coli is a mesophile that grows best at 37 degrees Celsius in neutral pH environments. E. coli is a facultative aerobe and is able to grow without oxygen, but it can extract more energy from its nutrient source and grow faster if oxygen is present.
If a bacterial culture is incubated at a temperature that is above the maximum growth temperature of that organism, what effect will that have on its cellular enzymes? they can pack tightly and solidify, prohibiting the membrane from functioning properly.
Optimal Growth ConditionsDifferent bacteria like to grow at different temperatures. By changing the temperature, he can study the bacteria while they are stressed. Organisms that grow best at human body temperature, which is approximately 37 degrees Celsius (98.6 degrees Fahrenheit), are called mesophiles.
In general, the higher the temperature, the more easily microorganisms can grow up to a certain point. Very high and very low temperatures both obstruct the enzyme processes microorganisms depend on to survive, but individual species of microorganisms have grown to prefer different levels of temperature.
Bacteria grow most rapidly in the range of temperatures between 40 ° and 140 °F, doubling in number in as little as 20 minutes. If the temperature is above 90 °F, food should not be left out more than 1 hour.
Environmental changes such as temperature shifts induce genomic evolution, which in turn provides the bacteria with thermal-tolerant abilities to survive under high temperatures. Such evolutionary changes could be achieved through horizontal gene transfer (HGT), gene loss, or gene mutations (4).
Mesophilic bacteria grow best at lower temperatures than thermophilic bacteria. Mesophilic cultures grow at 50-108° F, with an optimum range between 77-86° F. Thermophilc cultures are frequently used in Italian-style cheeses such as parmesan, etc.
A mesophile is an organism that grows best in moderate temperature, neither too hot nor too cold. All human pathogens are mesophiles.
hyperthermophiles (“heat- lovers”) grow best at temperatures well above human body temperature. They do not cause disease in humans because they do not grow in humans.
What bacteria need to grow and multiply
- Food (nutrients)
- Water (moisture)
- Proper temperature.
- Time.
- Air, no air, minimal air.
- Proper acidity (pH)
- Salt levels.
When the temperature or pH of their environment falls outside this range, their growth is inhibited, and they may even die as a result of the adverse conditions. Therefore, only those microbes whose pH and temperature requirements match those conditions found in the human body will be able to grow and reproduce there.
We have investigated the growth of Escherichia coli, a mesophilic bacterium, as a function of pressure (P) and temperature (T). Escherichia coli can grow and divide in a wide range of pressure (1–400 atm) and temperature (23–40°C).
Psychrotrophic microorganisms have a maximum temperature for growth above 20°C and are widespread in natural environments and in foods. Psychrophilic microorganisms have a maximum temperature for growth at 20°C or below and are restricted to permanently cold habitats.
Bacteria grow most rapidly in the range of temperatures between 40 °F and 140 °F, doubling in number in as little as 20 minutes. This range of temperatures is often called the “Danger Zone.” Never leave food out of refrigeration over 2 hours.
On average, the occurrence of coliform bacteria was significantly higher when water temperatures were above 15 °C (Figure 10.2). Temperature is widely recognized as an important controlling factor in influencing bacterial growth. In climates where water temperatures are warm, bacterial growth may be very rapid.
In the light, both strains of bacteria take in more organic carbon, including sugars, metabolize them faster. In the dark, those functions are reduced, and the bacteria increase protein production and repair, making and fixing the machinery needed to grow and divide.
“Freezing food kills harmful bacteria that can cause food poisoning.” Bacteria can survive freezing temperatures. Freezing is not a method for making food safe to eat. When food is thawed, bacteria can still be present and may begin to multiply.
Viruses are actually protected by cold air. According to the National Institutes of Health, cold temperatures allow the virus's outer layer, it's envelope, to harden into a "rubbery gel." This protects the virus, allowing it to better transmit, or spread. Cold, dry conditions can also increase the spread of germs.
