TABLE 1.

Growth characteristics of wild-type and mouse-adapted H1N1 influenza virusesd

H1N1 virusVirus yieldPlaque sizec
EggsaMDCK cellsb
A/CA/04/097.5 ± 0.16.9 ± 0.10.2 ± 0.1
A/CA/04/09-MA18.2 ± 0.1*°8.1 ± 0.2*1.0 ± 0.2*°
A/CA/04/09-MA27.8 ± 0.1*°7.6 ± 0.4*0.5 ± 0.3°
A/TN/1-560/097.5 ± 0.16.6 ± 0.10.2 ± 0.1
A/TN/1-560/09-MA19.2 ± 0.3*°8.2 ± 0.2*°0.6 ± 0.2
A/TN/1-560/09-MA28.5 ± 0.1*°4.4 ± 0.1*°0.3 ± 0.1
  • a Values are mean log10 EID50/ml ± SD from three independent determinations. The EID50 in 10-day-old chicken eggs was determined with 10-fold serial dilutions of virus, incubated for 48 h at 37°C, and calculated by the Reed-Muench method (35).

  • b Values are mean log10 PFU/ml ± SD from three independent determinations. The PFU in MDCK cells was determined by plaque assay after 3 days of incubation at 37°C with 10-fold serial dilutions of virus (13).

  • c Values are mean plaque diameter (mm) ± SD as measured by using the Finescale comparator.

  • d *, P < 0.05 compared with the value for the respective wild-type virus (one-way ANOVA); °, P < 0.05 compared with the value for the respective mouse-adapted virus (one-way ANOVA).