The presence of potentially harmful bacteria in food is the leading cause of foodborne illnesses globally. It’s essential to understand the factors affecting the growth of harmful bacteria in food to reduce, prevent or eliminate the risk of bacterial contamination.
Any reference to bacteria in this article refers to the potentially harmful bacteria found in and on food products.
The 6 Factors Affecting Bacterial Growth Explained
The potentially harmful bacteria you can sometimes find in and on food need certain conditions to grow, survive and multiply. These conditions include food, acidity, temperature, time, oxygen and moisture.
In theory, it is only necessary to remove/control one of these factors to reduce or eliminate bacterial growth and make food safer.
For example, cooking food at high temperatures to kill bacteria. (TEMPERATURE factor)
Practically, it’s better to focus on removing/controlling two or more of these factors to make sure bacteria will not multiply to dangerous levels.
For example, cooking food at high temperatures to kill the bacteria AND store food out of the temperature danger zone as soon as possible to hinder bacterial growth. (TEMPERATURE and TIME factors)
1. Food (Nutrients)
Like most living things, the bacteria you can find in and on food also need a food source and nutrients to survive, grow and multiply.
Different bacteria have different nutritional needs, but food rich in protein and carbohydrates are the preferred choice for many bacteria.
Raw eggs, fish, poultry, cooked rice, and cooked pasta are a few examples of perfect food sources to encourage bacterial growth and thus pose a higher risk of contamination.
2. Acidity
Bacteria grow best in low acidic foods and do not grow in acidic environments lower than 4.6 pH. Any food with a pH level higher than 4.6 has the risk of increased bacterial growth.
The optimal range where bacteria thrive best is between 6.6 pH and 7.5 pH levels. You need to keep a close eye on food products falling within this pH range.
For example, poultry, fish, dairy and eggs (to only mention a few) are considered low acid foods and susceptible to bacterial contamination.
High acid foods like lemon juice and vinegar do not support bacterial growth and are often used as preservatives for low acid foods.
List of common food products and their pH levels
3. Temperature
Temperature plays an integral part in bacterial growth.
The ideal temperature range that encourages the growth and multiplication of bacteria is called the “Temperature Danger Zone (TDZ)” and ranges from 5°C to 60°C.
Within the TDZ, you can also find the “Extreme Temperature Danger Zone (ETDZ)”, which ranges from 25°C to 39°C. This is the range for optimal bacterial growth.
The TDZ also include room (ambient) temperature. Be careful of ambient temperatures falling inside the Extreme Temperature Danger Zone.
It’s important to keep food products outside the TDZ.
Temperature fast facts:
- Keep cold food cold and hot food hot.
- Chilling and freezing do not kill bacteria. Freezing put most bacteria “into hibernation” and chilling slows down bacterial growth dramatically. Bacteria are inactive while the food is frozen and will “wake up” as soon as the food thaws. Once thawed, any bacteria present on food left inside the TDZ will start to multiply rapidly.
- High temperatures above 60°C will kill bacteria, but not necessarily the toxins they might have already produced.
4. Time
Bacteria need time, in combination with the ideal conditions to multiply (reproduce).
A single bacterium cell can divide into two cells within 20-30 minutes, but it can also be as quick as every 15 minutes.
Extended time also allows some bacteria to produce harmful toxins.
The presence of small numbers of bacteria on food usually poses a low risk of becoming harmful. Still, extended time and the right conditions will allow the bacteria to multiply rapidly and can start producing toxins on the food, which poses a higher health risk.
Keep in mind that the bacteria can continue to multiply and even produce toxins once inside a person’s intestine. This means that a person eating contaminated food with only a few bacteria can eventually suffer from food poisoning.
It is crucial not to allow bacteria to grow. Keep high-risk food products outside the temperature danger zone (TDZ). If this is unavoidable, no more than 2 hours at ambient temperature or 1 hour if the food is stored within the Extreme temperature danger zone (ETDZ).
Discard any high-risk food products exposed to the TDZ or ETDZ for extended periods.
5. Oxygen
Most bacteria need oxygen to grow, survive and multiply. These bacteria are called “Aerobic bacteria”.
A few types of bacteria will only grow in oxygen-free environments. These bacteria are called “Anaerobic bacteria”.
The most well-known bacteria that thrive in an oxygen-free environment are Clostridium botulinum (botulism-causing) bacteria. Botulism is rare but extremely dangerous and can be found in canned foods when improperly processed and canned, especially home-canned, preserved, or fermented foods.
Storing food products in air-tight containers or vacuum-sealed packaging is an effective way to reduce the oxygen levels that bacteria need to grow in. Keep in mind some bacteria thrive in low oxygen environments.
6. Moisture
Bacteria need moisture to grow, survive and multiply. Foods containing high water content provide the ideal conditions for bacteria to thrive and multiply rapidly.
Raw meats, fish, poultry and raw eggs are good examples of foods with high water content and an ideal breeding ground for bacteria.
Dry and salted foods with lower water content have a lower risk of spoiling.
Conclusion
Bacteria need 6 conditions to grow, survive and multiply: food, acidity, temperature, time, oxygen and moisture.
If you take one, but preferably two or more of these factors out of the equation, it will prevent / reduce / eliminate bacterial growth.
In combination with improper storage practices, many high-risk food products provide the ideal conditions for potentially harmful bacterial growth.
It’s the responsibility of every food handler, food handling establishment and even consumers to ensure they understand the factors that promote bacterial growth to control the risk of contamination and foodborne illness.
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