TABLE 2.

Characterization of R292K, R371K, and R118K viruses^a

Reverse genetics virus	Growth of the virus in MDCK cellsb							NA activity (mean pmol/30 min ng−1 ± SD)	IC50 (nM)c
	C. perfringens NA	First passage		Third passage		Fifth passage
		Virus titer	Plaque size (%)	Virus titer	Plaque size (%)	Virus titer	Plaque size (%)		Oseltamivir carboxylate	Zanamivir
Wild type	−	7.4	L (100)	7.7	L (100)	7.5	L (100)	2,861.4 ± 107.2	0.5	2.8
R292K	−	3.4	S (100)	7.3	S (100)	7.5	S (97), L (3)	171.6 ± 33.9	>30,000 (+++)	19.9
	+	5.6	S (100)	7.3	S (100)	7.6	S (100)
R371K	−	4.0	S (100)	7.3	S (100)	7.0	S (100)	74.2 ± 25.4	23.4 (+)	46.3 (+)
	+	5.0	S (100)	7.4	S (100)	6.9	S (100)
R118K	−	<1.0	NAV	<1.0	NAV	<1.0	NAV	ND	ND	ND
	+	2.8	S (100)	5.8	S (99.3), L (0.7)	7.7	S (67.9), L (32.1)

^aData for the second and fourth passages were determined but are not shown for the sake of brevity. ND, not determined due to compromised growth of the virus.

^bThe recombinant viruses were grown in the presence (+) or absence (−) of 2 mU of C. perfringens NA/ml during the five serial passages in MDCK cells. NAV, not available. Virus titers were determined by plaque assay in MDCK cells in the absence of C. perfringens NA and expressed as the log₁₀ PFU/ml. Plaque sizes: S, small (0.2 to 0.6 mm in diameter); L, large (1.0 to 2.0 mm in diameter), as determined by the Finescale comparator (Los Angeles, CA). The percentage of small or large plaques is shown in parentheses.

^cDrug resistance is expressed as a multiple of the IC₅₀ of the wild-type virus as determined by NA inhibition assay: +, multiple > 10; ++, multiple > 100; +++, multiple > 1,000.