Table 1.
Drug susceptibility and genotype of influenza B/Ontario/RV75-11/2010 virusa
| Virus strain | Passage no. of isolate or description | NA change | Oseltamivir |
Zanamivir |
||
|---|---|---|---|---|---|---|
| IC50 (nM) | Fold increaseb | IC50 (nM) | Fold increaseb | |||
| B/Ontario/RV75-11/2010 | 1 | G109E | 19.87 ± 0.41 | 7 | 23.11 ± 1.57 | 6 |
| B/Ontario/RV75-11/2010 | 2 | G109E | 39.99 ± 5.99 | 13 | 69.29 ± 5.88 | 18 |
| B/Ontario/RV535/2011 | 1 | G109 | 3.60 | 1.2 | 6.37 | 1.7 |
| Controls | ||||||
| B/Hong Kong/45/2005 | Susceptible control | None (WTc) | 3.00 ± 0.47 | 1 | 3.83 ± 0.34 | 1 |
| B/Hong Kong/36/2005 | Resistant control | R371K | 633.33 ± 185.59 | 211.93 ± 89.38 | ||
The susceptibility to oseltamivir and zanamivir was determined by a chemiluminescence neuraminidase inhibition assay, using the NA-Star kit (Applied Biosystems Inc.). Neuraminidase (NA) inhibition was assayed with viruses standardized to equivalent NA enzyme activity and incubated with NA inhibitor (NAI) at concentrations of 0.0316 nM to 1,000 nM. The 50% inhibitory concentration (IC50) was calculated by plotting the percentage of inhibition of NA activity against the inhibitor concentration, using GraphPad PRISM 4 software for curve fitting.
Fold increase in the IC50 compared to the values for the wild-type control B/Hong Kong/36/2005 for oseltamivir and zanamivir.
WT, wild type.