A method for identifying a nucleic acid which codes for a polypeptide factor affecting the covalent bonding of polypeptides to the surface of Gram-positive bacteria, comprising the following steps: a) providing a sample of Gram-positive bacteria which can be genetically altered and contain or produce at least one enzymatic reporter substance which is or can become covalently bonded to the surface of the Gram-positive bacteria, said at least one reporter substance having a different enzymatic activity when not covalently bonded to the surface of the Gram-positive bacteria from that exhibited when it is covalently bonded to the surface of the Gram-positive bacteria; b) causing genetic alterations in Gram-positive bacteria of the sample; c) assaying the enzymatic activity of the reporter substance of the Gram-positive bacteria of the sample; d) separating Gram-positive bacteria which exhibit a different enzymatic activity of the reporter substance from that observed for covalent bonding of the reporter substance to the surface of the Gram-positive bacteria; e) isolating the nucleic acid of the Gram-positive bacteria separated in step d); f) identifying at least one segment of the nucleic acid isolated in step e) that carries the genetic alteration; g) based on the segment identified in step f), identifying a nucleic acid which codes for a polypeptide factor affecting the covalent bonding of polypeptides to the surface of Gram-positive bacteria.