Catalyzes the N-deacetylation of poly-beta-1,6-N-acetyl-D-glucosamine (PNAG, also referred to as PIA), a biofilm adhesin polysaccharide. In fact, the IcaB deacetylase converts 15 to 20% of the GlcNAc residues of PNAG to glucosamine. N-deacetylation is crucial for attachment of the polysaccharide to the bacterial cell surface; it leads to the introduction of positive charges in the otherwise neutral PIA polymer, allowing electrostatic interactions. Deacetylation of the polymer is also essential for key virulence mechanisms of S.epidermidis, namely biofilm formation, colonization, and resistance to neutrophil phagocytosis and human antibacterial peptides 