MadSci Network: Microbiology

Re: why won't bacteria grow in a high sugar environment?

Date: Tue Mar 7 20:48:49 2000
Posted By: George Stearns, Grad student, Food Microbiology, University of Nebraska-Lincoln
Area of science: Microbiology
ID: 952455753.Mi

The question that Cassi asked "why won't bacteria grow in a high sugar environment?" is a good one. The principal behind bacteria not growing in this type of environment is actually one of the common food preservation techniques that have been used for centuries, even though people may not have known how they were actually preserving the food. The reason for most bacteria's inability to grow in a high sugar environment is the same as the reason for their inability to grow in high salt environments.

Both sugar and salt bind up the water and thus makes the water unavailable to the bacteria to use. In essence, while the environment may seem like it has a lot of water in it, most of the water is tied up by the salt or sugar. Bacteria require a certain amount of "available" water to survive and grow. Spoilage of jams and jellies is usually due to molds and not bacteria because of the high sugar content. Molds do not require as much water for growth and survival as most bacteria.

There are some bacteria that can grow in situations where there is a high salt or sugar content, but these species are usually not found in the bathroom. I am not familiar with a "high sugar agar" so I do not know the sugar concentration. If any bacteria do grow on the agar they would most likely will be species of Staphylococcus (Staph). Staph has an higher salt tolerance than many other bacteria. If you need an actual source that states this information any Food Microbiology textbook with a section on food preservation techniques should serve the purpose.

I would like to encourage Cassi to pursue her interest in being a Food Scientist. There are many different aspects of Food Science that a person can pursue. Due to the variety of subjects under the realm of Food Science anyone can find an area that matches their strengths. Food Engineering requires someone with good math skills and a desire to learn engineering. Food Chemistry relies on people with an aptitude for chemistry. There are many different aspects to the field and there are many good universities that offer degrees in Food Science. I wish Cassi the best of luck in pursuing her goal of becoming a Food Scientist.

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