Priv. Doz. Dr. Ingo Maier
Labor für Mikrobiologie und Ökosystemforschung
ecoscope · Hochgratweg 12 · 88279 Amtzell · Germany
Leica Biosystems GmbH
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69226 Nussoch
Germany
Hochgratweg 12
88279 Amtzell, Germany
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CERTIFICATE
Inactivation of pathogens by UV-C in the Leica cryostat product family with
particular focus on coronaviruses
ADDENDUM to Maier, I (2010): Certificate: Inactivation of bacteria, viruses and other pathogens
by UV-C irradiation in the Leica cryostat product family
A family of Leica cryostats is equipped with germicidal UV-C lamps (254 nm) that provide
disinfection of the working space in a safe and convenient way. UV-C irradiation is an efficient
and well-established technology for the inactivation of microorganisms in sensitive areas.
Besides aerosols, contaminated surfaces are a potential source for the spread of viruses. This is
especially true for high-touch fomites that are shared by multiple users. In the following, the
inactivation of coronaviruses by UV-irradiation in the cryostats will be addressed.
The main UV emission line of ionized mercury at 254 nm is close to the absorption maximum of
DNA and RNA and causes the photochemical dimerization of adjacent pyrimidine nucleotides.
Consequently, nucleic acid transcription is inhibited (Douki et al. 2003, Ravanat et al. 2001). UVC inactivation efficacy depends primarily on the target (genome) size and shielding by other UVC absorbing material (including water) as well as nucleic acid composition and conformation.
In UV-C-inactivation studies, test bacteria and viruses were dried onto stainless steel surfaces,
placed in the cryostat working space at - 20 °C and irradiated for various periods of time. As a
biodosimetry virus, simian virus 40 (SV40) was inactivated by >4 log10 units by irradiation for 95
to 180 minutes (Maier 2010). From these experiments and by comparison with published data,
predictions can be made on the efficacy of UV-irradiation for inactivation of microorganisms
and viruses for which empirical data are lacking. From a literature review, a mean radiation
dose of about 290 mJ/cm2 for reduction of polyomaviruses by 4 log10 units was deducted. SV40
is regarded as a highly UV-C-resistant virus (Maier 2010, Nims & Plavsic 2013).
Coronaviruses (CoV) in general cause various respiratory and enteric diseases in humans and
animals. At present, we are facing an unprecedented pandemic with hundreds of thousands of
deaths caused by SARS-CoV-2, the Severe acute respiratory syndrome related coronavirus 2.
Other life-threatening diseases are caused by SARS-CoV-1 and the Middle East respiratory
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UV-C disinfection in Leica cryostats
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syndrome related coronavirus (MERS-CoV). The genus also includes, for example, several
human coronaviruses (HCoV), responsible for mild to moderate respiratory tract infections,
Porcine epidemic diarrhea virus (PEDV) and Canine coronavirus (CCoV).
Coronaviruses are large enveloped single-stranded RNA viruses with a genome size of about 30
kb (Lee 2015, Lu et al. 2020, Marra et al. 2003, Rota et al. 2003, van Boheemen et al. 2012). Due
to large target size, the single-stranded genome and presence of a lipid envelope,
coronaviruses, including SARS-CoV-2, are highly susceptible to UV-C radiation as well as to
chemical disinfectants. Application of UV-C technologies for the reduction of virus transmission
is thus urgently recommended, as has already been put forward by Garcia de Abajo (2020),
Hadi et al. (2020), Heilinghoh et al. (2020), Heßling et al. (2020) and others.
Bedell et al. (2016) showed MERS-CoV and Mouse hepatitis virus (MHV, a beta-coronavirus)
surface disinfection by >5 log10 units using an automated whole-room UV-C irradiation system
without information of the UV-C dose applied. For coronaviruses in aerosols and in
suspensions, D90 irradiation dose values (90 % inactivation, 1 log10 unit) of 0.7 - 2.1 mJ/cm2 have
been reported (Kowalski et al. 2009, Sagripanti & Lytle 2020, Walker & Ko 2007). Heßling et al.
(2020) estimate a ‘true’ D90 value of 3.7 mJ/cm2 for the inactivation of SARS-CoV-2 in
suspension, taking the large variation in published data and experimental limitations into
account. With the same dose, Bianco et al. (2020) achieved a reduction in virus titer of > 3 log10
units. Patterson et al. (2020) reported a reduction by ≥ 6 log10 units with 40 mJ/cm2. As
Kowalski et al. (2009), Pendyala et al. (2020) developed a genomic model to predict the
sensitivity of SARS-CoV-2 and MERS-CoV to UV-C, resulting in D90 values of 2.2 mJ/cm2 and 2.8
mJ/cm2, respectively.
In conclusion and by comparison with other single-stranded RNA viruses of similar genome size,
2.5 mJ/cm2 is regarded as a realistic D90 value, corresponding to 10 mJ/cm2 for a 4 log10
reduction. SARS-CoV-2, SARS-CoV and MERS-CoV are far less resistant to UV-C radiation than
SV40, the tested reference virus. It can thus be safely assumed that irradiation in the cryostat
for three hours (CM1850UV/CM1860UV/CM1950) and four hours (CM1900UV), respectively,
reduces coronavirus contamination by more than 4 log10 units.
Virus inactivation by UV-C is restricted to irradiated areas. Virus particles shielded by other
material like water, body fluids or tissue may not be affected. Therefore, aerosol formation and
inhalation of tissue debris should be avoided as much possible. UV-C irradiation cannot replace
regular chemical disinfection of the cryostat chamber.
Bedell K et al 2016. Efficacy of an automated multiple emitter whole-room ultraviolet-C disinfection system against
coronaviruses MHV and MERS-CoV. Infection Control & Hospital Epidemiology 37(5): 598-599.
doi:10.1017/ice.2015.348
Bianco A et al 2020. UV-C irradiation is highly effective in inactivating and inhibiting SARS-CoV-2 replication.
medRxiv 2020.06.05.20123463. doi: 10.1101/2020.06.05.20123463
Douki T et al 2003. Inter-strand photoproducts are produced in high yield within A-DNA exposed to UVC radiation.
Nucleic Acids Research 31(12): 3134-3142. doi: 10.093/nar/gkg408
Garcia de Abajo FJ et al 2020. Back to normal: An old physics route to reduce SARS-CoV-2 transmission in indoor
spaces. ACS Nano 14(7): 7704-7713. doi: 10.1021/acsnano.0c04596
Hadi J et al. 2020. Control measures for SARS-CoV-2: A review on light-based inactivation of single-stranded RNA
viruses. Pathogens 9(9): 737. doi: 10.3390/pathogens90900737
Heilingloh CS et al 2020. Susceptibility of SARS-CoV-2 to UV irradiation. American Journal of Infection Control 48,
1273-1275. doi: 10.1016/j.ajic.2020.07.031
Heßling M et al 2020. Ultraviolet irradiation doses for coronavirus inactivation - review and analysis of coronavirus
photoinactivation studies. GMS Hygiene. and Infection Control 15:Doc08. doi: 10.3205/dgkh000343
ecoscope Labor für Mikrobiologie und Ökosystemforschung 88279 Amtzell Germany
UV-C disinfection in Leica cryostats
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Kowalski WJ et al 2009. Genomic model for the prediction of ultraviolet inactivation rate constants for RNA and
DNA viruses. In: Ultraviolet germicidal irradiation handbook. UVGI air and surface, International Ultraviolet
Association, Boston, MA, USA
Lee C 2015. Porcine epidemic diarrhea virus: An emerging and re-emerging epizootic swine virus. Virology Journal
12: 193. doi: 10.1186/s12985-015-0421-2
Lu R et al 2020. Genomic characterization and epidemiology of 2019 novel coronavirus: Implications for virus
origins and receptor binding. Lancet 395(10224): 565-574. doi: 10.1016/S0140-6736(20)30251-8
Maier I 2010. Certificate: Inactivation of bacteria, viruses and other pathogens by UV-C irradiation in the Leica
cryostat product family. ecoscope, Amtzell, 21 p.
Marra MA et al. 2003. The genome sequence of the SARS-associated coronavirus. Science 300(5624): 1399-1404
Nims RW, Plavsic M 2013. Polyomavirus inactivation - A review. Biologicals 41(2): 63-70.
10.1016/j.biologicals.2012.09-011
Patterson EI et al 2020. Methods of inactivation of SARS-CoV-2 for downstream biological assays. Journal of
Infectious Diseases 222(9): 1462-1467. doi: 10.1093/infdis/jiaa507
Pendyala B et al 2020. Genomic modeling as an approach to identify surrogates for use in experimental validation
of SARS-CoV-2 and HuNoV inactivation by UV-C treatment. Frontiers in Microbiology 11: 572331. doi:
10.3389/fmicb.2020.572331
Ravanat JL et al 2001. Direct and indirect effects of UV radiation on DNA and its components. Journal of
Photochemistry and Photobiology B 63: 88-102. doi: 10.1016/s1011-1344(01)00206-8
Rota PA et al. 2003. Characterization of a novel coronavirus associated with severe acute respiratory syndrome.
Science 300(5624): 1394-1399. doi: 10.1126/science.1085952
Sagripanti JL, Lytle CD 2020. Estimated inactivation of coronaviruses by solar radiation with special reference to
COVID-19. Photochemistry and Photobiology 96(4): 731-737. doi: 10.1111/php.13293
van Boheemen S et al 2012. Genomic characterization of a newly discovered coronavirus associated with acute
respiratory distress syndrome in humans. mBio 3: e00473-12. doi: 10.1128/mBio.00473-12
Walker CM, Ko G 2007. Effect of ultraviolet germicidal irradiation on viral aerosols. Environmental Science &
Technology 41(15): 5460-5465. doi: 10.1021/es070056u
Amtzell, 31 December 2020
Priv.-Doz. Dr. Ingo Maier
ecoscope Dr. Ingo Maier does not accept any responsibility for misleading citations due to
incomplete reproduction of this document.
ecoscope Labor für Mikrobiologie und Ökosystemforschung 88279 Amtzell Germany