Sialic acid-rich glycoproteins are important components of mammalian cells.  They are used by host cells to bind molecules on other cells.  In addition, sialic acid moitites can be shed and accumulate around cells or in the extracellular fluid where they act as decoys for pathogen binding.  Several pathogens,  some bacteria and a few viruses, have evolved virulence factors that utilize sialic acid to their benefit.  Propose two reasonable mechanisms for bacteria and or viruses to utilize host cell sialic acid or sialic acid-rich glycoproteins as virulence factors.  Don't just list them, describe your ideas and discuss the benefit to the pathogen for each mechanism you propose