title: Evaluation of virus inactivation by formaldehyde to enhance biosafety of diagnostic electron microscopy.
abstract: Formaldehyde (FA) fixation of infectious samples is a well-established protocol in diagnostic electron microscopy of viruses. However, published experimental data that demonstrate virus inactivation by these fixation procedures are lacking. Usually, fixation is performed immediately before the sample preparation for microscopy. The fixation procedure should transform viruses in a non-infectious but nonetheless structurally intact form in order to allow a proper diagnosis based on morphology. FA provides an essential advantage in comparison to other disinfectants, because it preserves the ultrastructure of biological material without interfering significantly with the preparation (i.e., the negative staining) and the detection of viruses. To examine the efficiency of FA inactivation, we used Vaccinia virus, Human adenovirus and Murine norovirus as models and treated them with FA under various conditions. Critical parameters for the inactivation efficiency were the temperature, the duration of the FA treatment, and the resistance of the virus in question. Our results show that FA inactivation at low temperature (4 °C) bears a high risk of incomplete inactivation. Higher temperatures (25 °C) are more efficient, although they still require rather long incubation times to fully inactivate a complex and highly robust virus like Vaccinia. A protocol, which applied 2% buffered FA for 60 min and a temperature-shift from 25 to 37 °C after 30 min was efficient for the complete inactivation of all test viruses, and therefore has the potential to improve both biosafety and speed of diagnostic electron microscopy.
authors: Advanced Light and Electron Microscopy (ZBS 4), Robert Koch Institute, Berlin D-13353, Germany. MoellerL@rki.de.
authors: Lars
authors: L
authors: Möller
authors: Highly Pathogenic Viruses (ZBS 1), Robert Koch Institute, Berlin D-13353, Germany. SchuenadelL@rki.de.
authors: Livia
authors: L
authors: Schünadel
authors: Highly Pathogenic Viruses (ZBS 1), Robert Koch Institute, Berlin D-13353, Germany. NitscheA@rki.de.
authors: Andreas
authors: A
authors: Nitsche
authors: Hospital Hygiene, Infection Prevention and Control (FG 14), Robert Koch Institute, Berlin D-13353, Germany. SchwebkeI@rki.de.
authors: Ingeborg
authors: I
authors: Schwebke
authors: Hospital Hygiene, Infection Prevention and Control (FG 14), Robert Koch Institute, Berlin D-13353, Germany. HanischM@rki.de.
authors: Manuela
authors: M
authors: Hanisch
authors: Advanced Light and Electron Microscopy (ZBS 4), Robert Koch Institute, Berlin D-13353, Germany. LaueM@rki.de.
authors: Michael
authors: M
authors: Laue
mesh_terms: D000818:Animals; D004202:Disinfectants / Q000494:pharmacology*; D004203:Disinfection / Q000379:methods* / Q000592:standards*; D004869:Equipment Safety; D005557:Formaldehyde / Q000494:pharmacology*; D006801:Humans; D008854:Microscopy, Electron; D038301:Virus Inactivation / Q000187:drug effects*; D014780:Viruses / Q000187:drug effects / Q000648:ultrastructure
chemical_list: D004202:Disinfectants; D005557:Formaldehyde