β-Propiolactone (BPL)-inactivation of SARS-Co-V-2: In vitro validation with focus on saliva from COVID-19 patients for scent dog training.

β-Propiolactone (BPL) is an organic compound widely used as an inactivating agent in vaccine development and production, for example for SARS-CoV, SARS-CoV-2 and Influenza viruses. Inactivation of pathogens by BPL is based on an irreversible alkylation of nucleic acids but also on acetylation and cross-linking between proteins, DNA or RNA. However, the protocols for BPL inactivation of viruses vary widely. Handling of infectious, enriched SARS-CoV-2 specimens and diagnostic samples from COVID-19 patients is recommended in biosafety level (BSL)- 3 or BSL-2 laboratories, respectively. We validated BPL inactivation of SARS-CoV-2 in saliva samples with the objective to use saliva from COVID-19 patients for training of scent dogs for the detection of SARS-CoV-2 positive individuals. Therefore, saliva samples and cell culture medium buffered with NaHCO3 (pH 8.3) were comparatively spiked with SARS-CoV-2 and inactivated with 0.1 % BPL for 1 h (h) or 71 h ( ± 1 h) at 2-8 °C, followed by hydrolysis of BPL at 37 °C for 1 or 2 h, converting BPL into non-toxic beta-hydroxy-propionic acid. SARS-CoV-2 inactivation was demonstrated by a titre reduction of up to 10^4 TCID50/ml in the spiked samples for both inactivation periods using virus titration and virus isolation, respectively. The validated method was confirmed by successful inactivation of pathogens in saliva samples from COVID-19 patients. Furthermore, we reviewed the currently available literature on SARS-CoV-2 inactivation by BPL. Accordingly, BPL-inactivated, hydrolysed samples can be handled in a non-laboratory setting. Furthermore, our BPL inactivation protocols can be adapted to validation experiments with other pathogens.