Purpose: This study was undertaken to characterize the efficacy of four commercial QACs against HuNoV GII.4 Sydney and a cultivable surrogate, Tulane virus (TuV).
Methods: HuNoV GII.4 Sydney positive stool (20% suspension), TuV cell culture lysate, and GII.4 virus-like particles (VLPs) were used in this study. Virucidal suspension assays were conducted in accordance with ASTM International standard E1052-11 using exposure times of 5, 10, 20, and 30 min. Analysis of degree and mode of GII.4 HuNoV inactivation was evaluated using a combination of RT-qPCR with RNase pre-treatment and SDS-PAGE. Analysis of TuV infectivity was done by plaque assay using LLC-MK2 cells.
Results: RT-qPCR assay results showed a 1.1±0.2 and 1.8±0.2 log10 reduction in HuNoV genome copies after 10 and 30 min exposure to QAC4, respectively. QACs 1 through 3 produced <1 log10 reduction following exposures of up to 30 min. QAC4 was, therefore, chosen for additional screening with TuV and GII.4 VLPs. A 1.3±0.2 log10 reduction in TuV infectivity following a 0.5 min exposure to QAC4 was observed and infectivity was eliminated following a contact time of 5 min. SDS-PAGE of HuNoV VLPs exposed to QAC4 for up to 30 min showed minimal capsid damage, suggesting the mechanism of action is not peptide bond cleavage.
Significance: Collectively, this study demonstrated limited efficacy of QACs against HuNoV, but greater sensitivity of the TuV surrogate. The behavior of cultivable surrogates may not always be representative of HuNoV. Consistent with currently held beliefs, the QACs evaluated here, with currently available methods, would have only partial utility for HuNoV inactivation.