Conditions favorable for the growth and multiplication of bacteria in food

At very high or very low temperature bacteria can neither survive nor reproduce. But at an optimum condition of about the normal body temperature of human or between the temperature range of 37oC to less than 60oC, bacteria are known to thrive and reproduce to cause food poisoning. When bacteria are present in food items at a very large number, food poisoning occur but at a very small number, food poisoning does not occur. Base on this fact, for food poisoning to occur bacteria must be present at a very large quantity in food and for bacteria to be present in a very large quantity, there must be favourable condition for bacteria to survive and to reproduce.  For this to happened, the condition must be favourable for the bacteria. These conditions depend on different parameters which are sometimes depended on one another or independent on one another.  The most important of them is the temperature.

Most bacteria need oxygen (aerobic), others thrive without it (anaerobic). Some bacteria tolerate the presences of salt better than others and we take advantage of this when curing meats. All of them hate cold, and round 32oF, (1000C) they become lethargic and dormant when the temperature drops lower keeping them at lower temperatures does not kill them, but only stops them from multiplying. At an elevated temperature above it optimum temperature or at lowered temperature the bacteria are kill or inhibited respectively, therefore they cannot cause food poisoning. Once the conditions are favorable again, they will wake up and start growing again. When food products are keep and a very high temperature or very low temperature, the rate at which bacteria reproduce is reduce thereby not being able to cause food poisoning. When the temperature is raised above 600C (1400F), it kills bacteria thereby hindering their ability to cause food poisoning.

Bacteria need the following condition for them to survive and reproduce to cause food poisoning:

  1. Water
  2. Food /nutrients
  3. pH
  4. Oxygen
  5. Temperature


  1. Water: When water or moisture is present, bacteria can cause food poisoning but when moisture of water is absent, bacteria cannot cause food poisoning. Bacteria need water to dissolve food for them to thrive and reproduce to a large number capable of causing food poisoning. Water allows the food to get into the cells, is used for the many chemical reactions necessary for life and growth, and allows waste products to escape. It is a very common practice to dry food items such as meat or fish to preserve them. The drying the food items commonly practice is to remove moisture (water) from it thereby preventing it from poisoning since bacteria cannot survive without moisture. Water or moisture is a very important condition for bacteria to cause food poisoning.
  2. Food/Nutrients: The occurrence of food poisoning by bacteria needs food/nutrient for the bacteria. The presence of sources of energy encourages the growth of bacteria to a very high level that can enable them to cause food poisoning, while the absence of these food items inhibit the growth of bacteria thereby reduces the likelihood of the bacteria to cause poisoning. Bacteria need energy for its existence and this energy occurs in food items such as sugars, starch, protein, fats and others compounds provide the nutrients.
  3. PH: When the pH is favourable the bacteria can survive and reproduce to a large number thereby causing food poisoning but when it is not the bacteria cannot. The acidity or alkalinity of food item is an important determinant whether bacteria can cause food poisoning in the food or not. The pH of a substance is measured with a pH which has a scale of 0 to 14 with 7 being neutral. PH is a term used to determine the acidity or alkalinity of a substance.  If the PH value is below 7, the food is classified as acidic. And when it is above 7 it is classified as an alkaline.  Most bacteria grow well at neutral pH which is 7, but a lot of them can tolerate a pH range from 4.5-10.0.
  4. Oxygen: There are bacteria that require oxygen for them to survive and reproduce, such bacteria are referred to as aerobic bacteria while others do not need oxygen for them to survive and reproduce. These bacteria are referred to as anaerobic bacteria. Depending on the nature of the bacteria, the present and absent of oxygen will determine whether the bacteria will be able to survive and cause food poisoning. For bacteria that need oxygen, the presence of oxygen is a favourable condition for them to cause food poisoning while the absence of oxygen will prevent them from causing food poisoning. While for bacteria that are anaerobic, the absence of oxygen is a favourable condition for them to cause food poisoning while the presence of oxygen will inhibit them from causing food poisoning.
  5. Temperature: The temperature of food or food products will determine whether bacteria will cause poisoning or not. At very high temperature or at very low temperature, bacteria cannot survive or reproduce. Based on this on this situation, food keep at a very high or low temperature are preserved from food poisoning. The temperature of the food is important in determining whether bacteria will cause food poisoning or not. Bacteria can thrive at a temperature around 320C – 600C but the optimum temperature for bacteria is between 36.60C to 40o
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