Infectious titers were significantly higher for all the combined isolates as compared with those of ECwt, particularly at 10 and/or 12 h.p.i. in Sp2/0-Ag14 cells (Fig 2A), whereas only WTEW and WWM exhibited higher infectious titers in Sp2/0-Ag14 cells at the last post-infection times (Fig 2B). This evidence concerns the gene SP2 and infection.