Continuous culture of Nosema mesnili NM-HC-A8801 (microsporida: nosematidae) in four lepidopteran cell lines

Spores of Nosema mesnili NM-HC-A8801 primed with 0.1 N KOH solution were inoculated into four lepidopteran cell lines (Antheraea eucalypti, Spodoptera frugiperda SF21AEII, Bombyx mari BmN-4, and Trichoplusia ni hi5), and the microsporidian growth and spread of infection were investigated. At a ratio of 30 spores per cell, 3% to 5% of host cells were infected initially with sporoplasms at 1 h post-inoculation. The number of the parasites in an infected cell started to increase at 24 h post-inoculation, depending on the merogony of N, mesnili NM-HC-A8801. At 48 h post-inoculation, when secondary infective forms appeared, rapid increases were observed in the number of parasitized cells. The percentage of infected cells at 120 h post-inoculation in the A. eucalypti, S. frugiperda SF21AEII, and B. mori BmN-4 cell lines reached approximately 90%, 60%, and 20%, respectively. Persistent infections of N. mesnili NM-HC-A8801 could be maintained through several passages of these cell cultures. In particular, the A. eucalypti and S. frugiperda SF21AEII cell lines showed high compatibility with this microsporidium. On the other hand, only 4% of T. ni hi5 cells were infected at 120 h post-inoculation, and infected cells disappeared after the second passage.