Abstract
Influenza A and B viruses possess a neuraminidase protein that shows sialidase activity. Influenza virus-specific neuraminidase inhibitors (NAIs) are commonly used for clinical treatment of influenza. However, some influenza A and B viruses that are resistant to NAIs have emerged in nature. NAI-resistant viruses have been monitored in public hygiene surveys and the mechanism underlying the resistance has been studied. Here, we describe a new assay for selective detection and isolation of an NAI-resistant virus in a speedy and easy manner by live fluorescence imaging of viral sialidase activity, which we previously developed, in order to achieve high-efficiency capture of an NAI-resistant virus. An NAI-resistant virus maintains sialidase activity even at a concentration of NAI that leads to complete deactivation of the virus. Infected cells and focuses (infected cell populations) of an oseltamivir-resistant virus were selectively visualized by live fluorescence sialidase imaging in the presence of oseltamivir, resulting in high-efficiency isolation of the resistant viruses. The use of a combination of other NAIs (zanamivir, peramivir, and laninamivir) in the imaging showed that the oseltamivir-resistant virus isolated in 2008 was sensitive to zanamivir and laninamivir but resistant to peramivir. Fluorescence imaging in the presence of zanamivir also succeeded in selective live-cell visualization of cells that expressed zanamivir-resistant NA. Fluorescence imaging of NAI-resistant sialidase activity will be a powerful method for study of the NAI resistance mechanism, for public monitoring of NAI-resistant viruses, and for development of a new NAI that shows an effect on various NAI-resistant mutations.