Define Bacterial Growth

Living beings grow because their cells divide and multiply. Even though bacteria only have one cell, their growth is also defined as an increase in number of cells, not an increase in their size.
Bacteria have specific requirements for their growth, and different species have different preferable growth conditions. By understanding growth requirements, we can determine how to control the growth of harmful bacteria and how to encourage the growth of those beneficial to us.

Meaning of Bacterial Growth

For most bacteria, growth involves increase in cell mass and duplication of the bacterial DNA, synthesis of new cell wall and cellular membrane, and finally cell division. This asexual process of reproduction is called binary fission. One bacterial cell divides into two cells, two cells into four, and so on.

Growth Requirements

Most bacteria, such as those that cause diseases and food spoilage, grow well at temperatures and pH (acidity or alkalinity of the environment) favored by humans. Bacteria also require water, since they are composed of 80-90 percent water, and they obtain most of the nutrients from water.
Bacteria need carbon, nitrogen, sulfur and phosphorus to build their proteins, carbohydrates, fats, DNA and RNA. Some bacteria, known as aerobic bacteria, require oxygen for their growth. They produce more energy from nutrients than anaerobic bacteria---bacteria that grow in the absence of oxygen.

Growth Phases

By observing laboratory bacteria, scientists discovered four basic phases of bacterial growth. The first phase is a period of little or no cell division, but of intense metabolic activity within the cells. The growth phase is when the bacteria begin to divide and are most metabolically active. In the stationary phase, or the period of equilibrium, the growth rate slows, because the number of bacterial deaths balances the number of new cells. In the death phase the number of deaths exceeds the number of new cells, which leads to death of the whole population. Bacteria can circumvent the death phase if they obtain fresh nutrients and if the dead bacteria are removed from the population.

Growth of Pathogenic Bacteria

Bacteria that cause diseases in plants, animals or humans are pathogenic bacteria. Some of them grow exclusively within the host cells, some in the cellular surrounding, and some in both environments. But what they all have in common are mechanisms that help them avoid being killed by the host. Their main aim is to multiply, to grow. And, indeed, the growth rate of pathogenic bacteria largely exceeds that of the host cells.

Control of Bacterial Growth

The control of bacterial growth is important in medicine, agriculture and food science. It usually involves the use of agents that either kill bacteria or prevent their growth.
Heat, irradiation, filtration, chemicals and gases are used for sterilization to completely destroy or eliminate all viable bacteria in a substance being sterilized. To reduce the number of bacteria in order to preserve food, people use refrigeration, drying and mild heat preservation, called pasteurization. To kill or inhibit the growth of pathogenic bacteria, we use antibiotics and chemical antiseptics, such as alcohol or iodine.