The Effects of Ultraviolet Light on Bacterial Growth

In laboratories and health care facilities, ultraviolet light can be used to sterilize work spaces, some equipment and tools. Ultraviolet sterilization can also be used to control bacteria in food, air, aquariums and ponds.

Mechanism

• Ultraviolet light causes two thymine (a compound that is an essential part of DNA) molecules that are next to each other on the bacteria’s DNA strand to dimerize (form a single molecule composed of two identical, thymine molecules).

Effect

• With all the thymine pairs on the DNA strand dimerized, the DNA cannot replicate. Sometimes, ultraviolet sterilization may not kill the bacteria outright, but the bacteria will not be able to reproduce, spread or cause disease.

Exception

• Because bacteria living in fissures, cracks and shadows can be shielded from ultraviolet rays, ultraviolet sterilization should only be used in conjunction with other sterilization techniques.

Types of Ultraviolet Light Used

• There are three wavelengths (185 nm, 254 nm and 265 nm) of ultraviolet light that are best for killing bacteria. A wavelength is the distance, measured in the direction the wave is going, between two peaks in the wave that have the same phase of oscillation.

History

• After the early 1900s, ultraviolet sterilization declined in popularity as a preferred method of sterilization, but it is beginning to regain some of its former popularity because it does not generate toxic chemical by-products that other sterilization methods can generate.