Studies on cytopathic effects of BmNPV infection in three lepidopteran insect cell lines in MGM-448 medium

ABSTRACT

Three insect cell lines, namely, DZNU-Bm-1, DZNU-Bm-12, and NIAS-MaBr-92, were tested for susceptibilityto Bombyx mori nucleopolyhedrovirus (BmNPV). The cytopathic effects of infection on cultured cells wereobserved. BmNPV was then serially passaged in these cell lines to assess their long-term ability to supportBmNPV replication. The cell lines were cultured in MGM-448 medium supplemented with 10% fetal bovineserum. Virus inoculum was prepared from B. mori larvae infected with BmNPV. The early signs of infectionstarted appearing within 16–36 hours post inoculation (hr pi). DZNU-Bm-1 and DZNU-Bm-12 cells showedheavy clumping. NIAS-MaBr-92 cells lost their motility and tended to form loose aggregations. Cytopathiceffects such as hypertrophy of nuclei and increase in cell size were prominent in all three cell lines. Beginningof occlusion body (OB) formation in DZNU-Bm-1 was first observed at about 36–42 hr pi, whereas, inDZNU-Bm-12, they were observed only after 42 hr pi. NIAS-MaBr-92 cells exhibited OB formation onlyafter 84 hr pi. The large mature OBs were visible in DZNU-Bm-1 cells by 66 hr pi, whereas, in DZNU-Bm-12cells by 72 hr pi. Mature OBs were observed in NIAS-MaBr-92 cells only after 120 hr pi. A number of OBsper cell varied from 12 to 82 in DZNU-Bm-1, 3 to 23 in DZNU-Bm-12, and 3 to 14 in NIAS-MaBr-92 cells.In this study, DZNU-Bm-1 and DZNU-Bm-12 cell lines were found to be better than NIAS-MaBr-92 interms of percentage infection. The yield of OBs per infected cell is also the highest in DZNU-Bm-1, whereasDZNU-Bm-12 and NIAS-MaBr-92 have comparable yields of OBs per cell.