Table 1.
Antiviral susceptibility and genotype of an influenza B virus with an H273Y substitution that was recovered from a patient in Ontario, Canada, during the 2010 to 2011 influenza seasona
| Virus strain | Type/subtype | Passage/virus subsetb | NA mutation | Oseltamivir carboxylate |
Peramivir |
Zanamivir |
|||
|---|---|---|---|---|---|---|---|---|---|
| Mean IC50 ± SD (nM) | Fold difference | Mean IC50 ± SD (nM) | Fold difference | Mean IC50 ± SD (nM) | Fold difference | ||||
| B/Ontario/006876/2011 | B | Primary | H273Y | Not tested | Not tested | Not tested | Not tested | Not tested | Not tested |
| B/Ontario/006876/2011 | B | 1 | H273Y | 19.4 ± 0.65 | 11.4 | 11.12 ± 0.23 | 34.8 | 0.93 ± 0.66 | 1 |
| B/Memphis/20/96 | B | Reference | WT | 1.32 ± 0.85 | 1 | 0.32 ± 0.23 | 1 | 1.35 ± 0.37 | 1 |
| B/Memphis/20/96 | B | Reference | R152K | 156.25 ± 70.04 | 118 | 43.14 ± 15.32 | 134.8 | 38.82 ± 29.33 | 28.75 |
| A/California/07/2009 | A(H1N1)2009 | Reference | WT | 0.12 ± 0.04 | 1 | 0.08 ± 0.04 | 1 | 0.10 ± 0.06 | 1 |
| A/North Carolina/39/2009 | A(H1N1)2009 | Reference | H275Y | 81.25 ± 42.16 | 677 | 9.05 ± 1.54 | 113.1 | 0.26 ± 0.07 | 1 |
| A/Wuhan/395/95 | A(H3N2) | Reference | WT | 0.27 ± 0.11 | 1 | 0.23 ± 0.14 | 1 | 0.73 ± 0.29 | 1 |
| A/Wuhan/395/95 | A(H3N2) | Reference | E119V | 5.01 ± 2.18 | 18.5 | 0.19 ± 0.09 | 1 | 0.54 ± 0.17 | 1 |
Susceptibility to the neuraminidase inhibitors oseltamivir and zanamivir was measured by a chemiluminescent assay using the NA-Star kit (Applied Biosystems Inc.). NA inhibition was assayed with equivalent NA enzyme activity and incubated with increasing concentrations of NAI from 0.0316 to 1,000 nM. Curve fitting and the 50% inhibitory concentration were calculated by plotting percent inhibition relative to the NAI concentration using GraphPad Prism 4 software. NA, neuraminidase; NAI, neuraminidase inhibition; IC50, 50% inhibitory concentration; WT, wild type; SD, standard deviation; V, valine; H, histidine; Y, tyrosine; R, arginine; K, lysine. Mean IC50s for wild-type reference control viruses for each type/subtype are in boldface and were used to calculate the fold differences for their respective types/subtypes as indicated. IC50s for reference viruses represent the average taken from at least 5 replicates.
Reference, susceptible and resistant reference viruses used as controls in NAI assays.