Sentence:  [H]ydrolysis of sialic acid <WSD>moieties</WSD> by neuraminidase of myxoviruses facilitates cellular attachment and invasion, and the disturbed secretion and dispersion of mucin in cystic fibrosis facilitate colonization with "P. aeruginosa". 
Meaning of the word marked with <WSD> tags:  A specific segment of a molecule.