A reverse genetics study of resistance to neuraminidase inhibitors in an influenza A/H1N1 virus

A system of reverse genetics was used to generate influenza A/HlNl viruses harbouring neuraminiclase (NA) mutations previously associated with resistance to NA inhibitors in various viral subtypes. The His274Tyr and GIu1196In mutants were rescued whereas the Arg292Lys and 6110119 -> Gly, Val, Ala or Asp mutants could not be generated. In NA inhibition assays, the His274Tyr mutant was resistant to oseltamivir (430-fold over wild-type) and BCX-1812 (50-fold) but was sensitive to zanamivir. A similar trend was seen when the mutant was evaluated by plaque reduction assay (PIRA). The Glull96ln mutant expressed a low level of resistance to oseltarnivir (ninefold) and zanamivir (fourfold) in NA inhibition assay but was only marginally resistant to oseltarnivir (fourfold) in PRA. The replication capacity of both mutants, in particular that of the His274Tyr virus, was impaired when compared with the wild-type virus in vitro.