What change occurs to bacteria when exposed to ultraviolet light in an irradiator?

When bacteria are exposed to ultraviolet (UV) light in an irradiator, the primary change that occurs is the destruction of their DNA. UV light has a high energy level that can lead to the formation of pyrimidine dimers, particularly thymine dimers in the DNA of bacteria. These dimers disrupt the normal base pairing during DNA replication, resulting in mutations or complete inactivation of the bacteria's genetic material. As a result, the bacteria are unable to replicate, ultimately leading to cell death.

This understanding of the effect of UV light on bacteria is critical in various applications, such as sterilization and disinfection processes in healthcare settings, where controlling bacterial growth is essential for patient safety and infection control.