Responsible for addition of the terminal mannose residues to the outer chain of core N-linked polysaccharides and to O-linked mannotriose. Implicated in late Golgi modifications (By similarity). Protein modification; protein glycosylation. Induced during biofilm formation and Up-regulated in response to treatment with MUC7 12-mer, a cationic antimicrobial peptide derived from the N-terminal region of human low-molecular-weight salivary mucin. Belongs to the MNN1/MNT family.