Abstract

Three insect cell lines viz. DZNU-Bm-1, DZNU-Bm-12 and NIAS-MaBr-92 were tested for susceptibility to BmNPV. Cytopathic effects of infection on cultured cells were observed. BmNPV was then serially passaged in these cell lines to assess their long-term ability to support BmNPV replication. They were cultured in MGM-448 medium supplemented with 10% Foetal Bovine Serum (FBS). Virus inoculum was prepared from Bombyx mori larvae infected with BmNPV. Early signs of infection started appearing within 16-36 hours post inoculation (hr pi). DZNU-Bm-1 and DZNU-Bm-12 cells showed heavy clumping. NIAS-MaBr-92 cells lost their motility and tended to form loose aggregations. Cytopathic effects such as hypertrophy of nuclei and increase in cell size were prominent in all three cell lines. Beginning of OB formation in DZNU-Bm-1 was first observed at about 36-42 hr pi while in DZNU-Bm-12 they were observed only after 42 hr pi. NIAS-MaBr- 92 cells exhibited OB formation only after 84 hr pi. Large mature OBs were visible in DZNU-Bm-1 cells by 66 hr pi and in DZNU-Bm-12 cells by 72 hr pi. Mature OBs were observed in NIAS-MaBr-92 cells only after 120 hr pi. Number of OBs/cell varied from 12 to 82 in DZNU-Bm-1; 3 to 23 in DZNU-Bm-12 while 3 to 14 in NIAS-MaBr-92 cells. In present study, DZNU-Bm-1 and DZNU-Bm-12 cell lines were found to be better than NIAS-MaBr-92 in terms of percentage infection. Yield of OBs per infected cell is also highest in DZNU-Bm-1 while DZNU-Bm-12 and NIAS-MaBr-92 have comparable yields of OBs per cell.

Key words: Cytopathic effects; Serial passaging; Susceptibility; Insect cell line; DZNU-Bm-1