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How do UV rays kill microbes?

Q: How do UV rays kill microbes?

Krishna: Ultraviolet germicidal irradiation (UVGI) is an established means of disinfection and can be used to prevent the spread of certain infectious diseases.

We use this daily in our microbiology labs.

Low-pressure mercury (Hg) discharge lamps are commonly used in UVGI applications and emit shortwave ultraviolet-C (UV-C, 100–280 nanometer [nm]) radiation, primarily at 254 nm. UV-C radiation kills or inactivates microbes by damaging their deoxyribonucleic acid (DNA). (1)

The principal mode of inactivation occurs when the absorption of a photon forms pyrimidine dimers between adjacent thymine bases and renders the microbe incapable of replicating. UVGI can be used to disinfect air, water, and surfaces, although surface disinfection is limited by microshadows and absorptive protective layers. Water disinfection is currently the most advanced and accepted germicidal application. Air disinfection is accomplished via several methods: irradiating the upper-room air only, irradiating the full room (when the room is not occupied or protective clothing is worn), and irradiating air as it passes through enclosed air-circulation and heating, ventilation, and air-conditioning (HVAC) systems. UVGI is also used in self-contained room air disinfection units. (1)

UV rays kill microbes by damaging their genetic material (DNA and RNA), which prevents them from replicating and functioning. The UV photons are absorbed by the microorganism's nucleic acids, causing them to form abnormal bonds, specifically creating pyrimidine dimers in the DNA and RNA strands. This damage disrupts replication and transcription, leading to the death or inactivation of the microbe.

This is the usual process ....

Absorption of UV light: Microorganisms absorb UV photons, particularly in the UV-C range, through their genetic material.

Formation of pyrimidine dimers: The absorbed energy triggers a chemical reaction that causes covalent bonds to form between adjacent pyrimidine bases (like thymine in DNA and uracil in RNA).

Disruption of replication and function: These abnormal structures, known as pyrimidine dimers, physically block the enzymes needed for DNA replication and RNA transcription.

Inactivation or death: With their genetic code damaged, the microbes cannot reproduce or carry out necessary functions, leading to their inactivation or death.

Footnotes:

1. https://pmc.ncbi.nlm.nih.gov/articles/PMC2789813/#:~:text=Low%2Dpre...(Hg),their%20deoxyribonucleic%20acid%20(DNA).

How do UV rays kill microbes?

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