Sialidases from S. pneumoniae (A), C. perfringens (B) and Newcastle disease virus (C), which showed partial or low levels of H185 epitope hydrolysis by ELISA (Fig1A), were less efficient in hydrolyzing Neu5,7Ac2 and Neu5,9Ac2 from human tears than A. ureafaciens sialidase (step 1); further treatment of the digested tears with A. ureafaciens sialidase revealed the presence of remaining Neu5,7Ac2 and Neu5,9Ac2 derivatives in the samples (step 2).