Legionella Testing / Biosafety Training
legionella_banner.png

Blog

Dr Richard W Gilpin’s Blog

Are PCR Hoods Effective? No

PCR Hoods are claimed to remove residual DNA from the work area by UV-C radiation - do they?

Class II Type A2 Biosafety Cabinets are preferred over PCR Hoods for removal of residual DNA from the work area airstream by HEPA/ULPA filtration.
K.F. Held et. al, Applied Biosafety April 19, 2018 
HEPA filters are very effective at removing various-sized contaminants but do not prevent gases and vapors from penetrating through them. Researchers have speculated that DNA may not be captured by HEPA filters, allowing for contamination of subsequent experiments by aerosolized DNA. Here we found that DNA is captured by a HEPA filter at the same efficiency as the filter is rated and discovered that DNA cannot be dislodged from a HEPA filter.

Modern UV lamps create 254 ηm UV-C by electrical discharge through low-pressure gas (including mercury vapor) enclosed in an industrial quartz tube. Inorganic materials (metal and glass) are not affected by normal exposure to UV-C. Organic materials (synthetic filter media, gaskets, rubber, motor windings, electrical insulation, internal duct insulation, and plastic piping) can be rapidly degraded by UV-C. ASHRAE Journal 50:28, August 2008.

Life may have existed on Earth as early as 3.8 billion years ago. It is nevertheless reasonable to assume that early life may have been at the edge of “mutation meltdown” partly due to high levels of mutagenic UV. Early microorganisms developed strategies to repair UV damage. http://www.dnva.no/geomed/solarpdf/Nr_10_Hessen.pdf

Photoreactivation repair of germicidal UV-C damage to DNA involves rapid monomerization of pyrimidine dimers before they can enter DNA replication. Dimer splitting is accomplished by combined action of photoreactivation enzyme and visible radiation (380-430 nm wavelength). ASM News 65:795, 1999.

UV-C kill curves for microorganisms are performed in liquid or agar, not dried on surfaces. UV-C disinfection is much more efficient in aqueous environments.
https://www.researchgate.net/publication/292158745_Laboratory_and_field_applications_of_UV_light_disinfection_on_six_species_of_Legionella_and_other_bacteria_in_water

UV-C does not degrade nucleic acid sequences and therefore is not effective as a method to destroy contaminant nucleic acids. Appl. Environ. Microbiol. 60:4203-4206, November 1994.
http://aem.asm.org/content/60/11/4203.abstract?sid=f9e4e1c5-e85c-470b-8548-8cc1999eeba8

UV-C lamps with industrial quartz solarize within 6 to 9 months and no longer produce 254 ηm germicidal radiation.

NSF/ANSI Standard 49 - 2016 Biosafety Cabinetry: Design, Construction, Performance, and Field Certification does NOT recommend installation of UV-C lamps in BSC’s.
http://www.nsf.org/newsroom_pdf/NSF_49-2016_Annex_E.pdf