Infection of Chick Chorioallantoic Membrane (CAM) as a Model for the Pathogenesis of Cryptococcus gattii.

The use of embryonated egg as an alternative in the study of the pathogenesis of fungi is evolving. Although murine models are the "gold standard," embryonated egg models are also used to screen determinants of virulence among fungi species. This study was aimed at determining the virulence potential of Cryptococcus gattii strains R265, R272, and EJB18, and Malassezia sympodialis using chorioallantoic membrane (CAM) of embryonated egg. At a concentration of 107 cfu/ml, C. gattii R272 was more virulent than R265 in the egg model, while EJB18 had low virulence. The CAM model supported the growth of Malassezia sympodialis strain and induced the formation of hyphae. The formation of lesions by the organism and its re-isolation from CAM suggest that the model can be used for evaluating the virulence of C. gattii. Histopathology of CAM from both strains also revealed massive disruption of CAM. This study suggests that embryonated egg is a useful alternative tool to pre-screen Cryptococcus gattii strains to select strains for subsequent testing in murine models and could also be a potential medium for studying the hyphal growth in Malassezia species.