The only way to kill bacteria by temperature is by cooking food at temperatures of 165 degrees or more. Bacteria also die in highly acidic environments like pickle juice.
Bacteria grow quickly in food, especially if it is left in the "danger zone" of temperatures, between 40 degrees and 140 Fahrenheit.
What bacteria need to grow and multiply
- Food (nutrients)
- Water (moisture)
- Proper temperature.
- Time.
- Air, no air, minimal air.
- Proper acidity (pH)
- Salt levels.
Why it matters: Bacteria are among the fastest reproducing organisms in the world, doubling every 4 to 20 minutes.
Bacteria may grow across a wide range of temperatures, from very cold to very hot. A mesophile is an organism that grows best in moderate temperature, neither too hot nor too cold. All human pathogens are mesophiles.
Bacteria are all around us. Given good growing conditions, a bacterium grows slightly in size or length, new cell wall grows through the center, and the "bug" splits into two daughter cells, each with same genetic material. If the environment is optimum, the two daughter cells may split into four in 20 minutes.
Each microorganism has a temperature range over which it can grow. Psychrophiles grow best at temperatures < 15 °C. In nature, they are commonly found in deep ocean waters or in polar regions. Mesophiles, which grow between 15 and 45 °C, are the most common types of microorganisms and include most pathogenic species.
Organisms categorized as mesophiles (“middle loving”) are adapted to moderate temperatures, with optimal growth temperatures ranging from room temperature (about 20 °C) to about 45 °C. As would be expected from the core temperature of the human body, 37 °C (98.6 °F), normal human microbiota and pathogens (e.g., E.
Since as early as 1860, it has been recognized that three cardinal temperatures (minimum or base temperature Tb, optimum temperature, Topt and maximum temperature, TMax) describe the temperature range over which the seeds of a particular species can germinate (Bewley & Black, 1994.
Whereas essentially all eukaryotic organisms require oxygen to thrive, many species of bacteria can grow under anaerobic conditions. Bacteria that require oxygen to grow are called obligate aerobic bacteria.
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.
Most bacteria grow best around neutral pH values (6.5 - 7.0), but some thrive in very acid conditions and some can even tolerate a pH as low as 1.0. Such acid loving microbes are called acidophiles.
Some of the important factors affecting bacterial growth are:
- Nutrition concentration.
- Temperature.
- Gaseous concentration.
- pH.
- Ions and salt concentration.
- Available water.
Enzymes cannot reproduce themselves. They speed up chemical reactions without getting used up themselves. All enzymes are proteins, and some enzymes attack proteins. Therefore, enzyme usefulness is limited by digestion from other enzymes Chemicals are NOT alive.
Fungal and bacterial growth rates had optimum temperatures around 25-30 degrees C, while at higher temperatures lower values were found. This decrease was more drastic for fungi than for bacteria, resulting in an increase in the ratio of bacterial to fungal growth rate at higher temperatures.
psychrophilic or cryophilic) are extremophilic organisms that are capable of growth and reproduction in low temperatures, ranging from −20 °C to +10 °C. They are found in places that are permanently cold, such as the polar regions and the deep sea.
Environmental Factors affecting Microbial Growth
- Moisture.
- Oxygen.
- Carbon Dioxide.
- Temperature.
- pH.
- Light.
- Osmotic Effect.
- Mechanical and Sonic Stress.
Nutrients are necessary for microbial growth and play a vital role in the proper cultivation of microorganisms in the laboratory and for proper growth in their natural environments. The types of nutrients that are required include those that supply energy, carbon and additional necessary materials.
Bacteria usually grow in the 'Danger Zone' between 8°C and 60°C. Below 8°C, growth is stopped or significantly slowed down. Above 60°C the bacteria start to die.
Low Risk FoodsBy removing moisture, (with sugar or salt), or by using a vinegar, (pickle), you are effectively taking away one of the four main elements that bacteria need to survive. It is rare for these foods to be associated with food poisoning outbreaks.
Food held between 5oC and 60oC for less than 2 hours can be used, sold or put back in the refrigerator to use later. Food held between 5oC and 60oC for 2-4 hours can still be used or sold, but can't be put back in the fridge. Food held between 5oC and 60oC for 4 hours or more must be thrown away.
The bacteria Listeria has been in the news a lot lately, linked to ice cream, frozen vegetables and fruit. Unlike most bacteria, Listeria can grow and multiply in your freezer and refrigerator. This is surprising to some. These bacteria can be killed by proper cooking and pasteurization.
Time – in ideal conditions, one bacterium can multiply to more than two million in seven hours. Temperature – food poisoning bacteria grow best in the temperature range between 5 °C and 60 °C. This is referred to as the 'temperature danger zone'.
