Bacterial Growth Requirements

Bacteria are single celled organisms that can only be seen with a microscope. They are so small that scientists measure them in micrometers. A micrometer is equal to one millionth of a meter. On average, a

bacterium is equal to one micrometer long. This would mean that the head of a pin could hold hundreds of thousands of these microorganisms.

Bacteria, which can be traced back 3.5 billion years, live all around us and also inside us. They are in the air, soil and water of the earth and in plants and animals as well. In humans bacteria can be found in many places. They are on skin surfaces, the inner surfaces of our nose, throat, stomach and intestines, to name a few. The only places you normally don’t find bacteria in our bodies, according to Encarta,” is in the muscles, blood and the nervous system.” They can, however, invade these areas and cause our immune system to get rid of them. Generally, most bacteria live in or on our bodies and help prevent disease. (pg.2)

According to Alcamo’s Fundamentals of Microbiology,” growth in the microbial world usually refers to an increase in the population size”. Bacteria reproduce asexually using a process called binary fission. Binary fission involves cytokinesis which is an inward pinching of the cell wall that separates it into two. This process occurs after a cell has grown large enough to divide. Under the right conditions some bacteria can reproduce in 15 to 20 minutes. This means that one cell can become two in that time and those two will then become four cells in about half an hour. After 6 hours, in ideal conditions, one bacterial cell can become 131,000 or more bacteria. (pg.139)

In order for bacteria to grow and reproduce they need nutrients and other outside factors. The nutrients are absorbed through pores in the cell wall and passed into the cytoplasm. Some examples of the factors important to cell growth are oxygen, temperature and pH level. “A thermophile grows at high temperatures, an acidophile grows at low pH, and an osmophile grows at high solute concentration,” are according to, which shows how the names correspond with growth conditions. (pg.8)

Temperature has been deemed one of the most important factors for growth because each species has an ideal growth temperature. The temperature range for these bacteria is a range of approximately 30 degrees with their ideal temp being somewhere in the middle. For example, “the thermophiles mentioned earlier multiply best at 60 degrees Celsius but still multiply between 40 and 70 degrees,” according to Alcamo’s Fundamentals of Microbiology. They tend to multiply better at the higher temperatures than they do at the lower ones. There are, however, cells that are opposite of this and would multiply better at lower temperatures than they would at the higher ones. (pg.147)

The next factor important for growth is oxygen. Many bacteria depend highly on oxygen and those are called aerobic cells. Oxygen in aerobic cells is used to make energy which is important for cell function and growth. There are, however, cells that don’t need oxygen and these are called anaerobic. Anaerobic cells would, obviously, use means other than oxygen for their energy source.

The pH level, which refers to the acidity or alkalinity level, is very important to bacterial cells. The cytoplasm in most of them has a pH level of 7.0 which is in the neutral range. This would make it important for these cells to be in an environment with a similar level in order for them to grow. There are cells that are more tolerant to lower acid levels and can survive in them. However, the majority don’t grow well in acidic environments. In the human body this is good news for the stomach. The acid levels here would help deter disease and keep bacteria from reaching other areas beyond the stomach.

As stated previously, bacteria are everywhere and in most cases are harmless and beneficial. However, there are bacteria that cause disease and when the immune system is not functioning properly they can invade areas of the body. Generally harmless bacteria can also become a problem if they enter the body through a cut or injury and make their way into the bloodstream. The bloodstream is one of the areas bacteria are not normally found and in the case of a weak immune system it would be an ideal place for them to multiply. For many cells the temperature, oxygen and pH levels are perfect in the bloodstream, for growth, and this can cause many problems for the human body. Other places that bacteria can grow which are harmful to a person are food and water. When they multiply to high numbers on things that we ingest it can cause food poisoning and other serious and sometimes deadly diseases.

The human immune system is designed to help keep bacteria counts at a normal range to keep us healthy and to fight off attacks of harmful bacteria. There are also other ways in which we can protect ourselves if our immune system is weak. One way is through antibiotics which are antibacterial drugs that are a very important part of the battle with bacteria. However, in time bacteria can become immune to antibiotics so they are no longer effective. Other ways to insure good health and good bacteria counts is through vaccines and maintaining healthy clean environments. These methods will help to prevent bacteria spread and a large number of health issues that go along with it.

Marquis, Robert E. (2007). Bacteria. Retrieved June 29, 2007, from

Pommerville, Jeffrey C. (2007) Alcamo’s Fundamentals of Microbiology. Eighth Edition.

Todar, Kenneth (2004) University of Wisconsin-Madison Department of Bacteriology.
Nutrition and Growth of Bacteria. Retrieved June 25, 2007, from