In vitro quantitative assessment of Echinococcus multilocularis metacestode viability after in vivo and in vitro...

The aim of this study was to apply the enzymatic MTT (3,5 dimethylthiazol-2yl)-2,5-diphenyl tetrazolium bromide--formazan colorimetry for quantifying the viability of Echinococcus multilocularis whole cysts, after maintenance in vivo or in vitro. The enzymatic activities of young cysts freshly removed from rodents were linearly correlated with the parasite cyst weight. A comparative evaluation of the MTT assay and the in vitro viability assessments showed that the number of animals used for drug-screening purposes would be reduced by 35.8%. In this way, the use of different parasite samples removed from the same host is required, because of their different ages and their subsequent different abilities to reduce MTT. Cysts removed from mice exhibited higher colorimetric values than those removed from jirds. Thus, small entire cysts obtained from mice were maintained in the CMRL 1066 culture medium. Their enzymatic activities were evaluated at different times. The results indicate that, in such conditions, the optimal period of time for testing the effect of drugs against the metacestodes is limited to the 10 days following their transfer from mouse to culture flasks. The MTT assay encourages further studies to improve the viability of the whole cysts in vitro, using other standardizable culture conditions.