Microbes grow everywhere. They exist in the air, in the food and in the water. Like other living organisms, microbes require an ideal environment to grow and flourish. These ideal environments may differ depending on the type of microbe. But the main factors that support microbial growth include temperatures, nutrients, acidity and osmotic pressure.
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Microbes can grow at a variety of temperatures. Scientists classify microbes according to the favoured temperatures for growth. According to the Food and Drug Administration (FDA), thermophiles flourish between the temperatures of 55 and 75 degrees Celsius. The group of microbes that typically infect humans are classified as thermophiles. These microbes, according to the FDA, grow rapidly at temperatures between 86 and 113 degrees Fahrenheit. Psychrophilic microbes, on the other hand, tend to grow at colder temperatures, between 54 and 59 degrees Fahrenheit. According to the FDA, psychrotrophs are capable of growing at very low temperatures, between 23 and 41 degrees Fahrenheit. But these microbes thrive at temperatures from 77 to 86 degrees Fahrenheit.
Microbes need nutrients to grow. The type of nutrients will vary based on the type of microbe. For microbes to grow, they may require water and energy, according to the FDA. Microbes usually derive energy from such sources as sugars, alcohols and fatty acids. Nutrients such as iron, sulphur and phosphorous also support microbial growth.
Acidity and alkalinity levels can also influence microbe growth. Most microbes grow at a more neutral pH range between 6.5 and 7.5. Some microbes can grow outside that pH range. Microbes such as Helicobacter pylori thrive in acidic areas such as the human stomach, which has pH below 6. Yeasts are another example of microbes that grow in acidic environments.
Microbes need the environment inside the cells to be in harmony with the environment outside the cells. Ideally, most microbes have a concentration of salt around 1 per cent in their cytoplasm and in their environment, keeping osmotic pressure at the desired balance. When the salt balance in microbes is thrown off, the environment inside the cell shifts. Added salt, for example, will remove water from the cell in an attempt to balance the levels of salt inside and outside an organism. When this process occurs, microbes shrink and die rather than grow. Some microbes, however, are tolerant of environments that have high salt concentrations.
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- U.S. Food and Drug Administration: Chapter 3. Factors that Influence Microbial Growth
- University of South Carolina School of Medicine: Bacterial Nutrition, Growth and Energy Metabolism
- Scientific American: How do salt and sugar prevent microbial spoilage?
- CliffNotes; Microbiology; Growth Requirements for Microorganisms