To reduce cytotoxicity when testing the virucidal activity of chemical disinfectants and biocides: The “T-25 method” as an alternative to “large-volume-plating”

When testing the virucidal activity of biocides, the non-inactivated residual virus is titrated on cell cultures by the end point dilution method on 96-well tissue culture plates. However, residues of the biocide to be tested also come into contact with the cell cultures in varying concentrations and thus can lead to cytotoxic effects even at high levels of dilution. In the European standards for testing biocides, in particular disinfectants, methods such as Large-Volume-Plating (LVP) method and, in some guidelines, gel filtration procedures are described for reducing cytotoxic effects in the case of highly cytotoxic products, if the classical dilution method proves to be impractical. In order to enable the testing of highly cytotoxic biocides for their activity against viruses, an alternative method for reducing cytotoxicity is introduced, which is based on a procedure of isolating infectious viruses from cytotoxic patients’ materials such as stool and can be applied when the other methods fail.