Detection of Staphylococcus aureus cell walls by enzyme-linked immunoassay using antibodies prepared from a semi-synthetic peptidoglycan precursor

Abstract

The peptidoglycan layer of Staphylococcus aureus contains a (Gly)₅ cross-link which is not found in other bacteria, and which could be used to develop a specific immunoassay for detection ofS. aureus in MRSA infections. A semi-synthetic route was used to prepare the S. aureuspeptidoglycan precursor UDPMurNAc-L-Ala-γ-D-Glu-L-Lys(Gly)₅-D-Ala-D-Ala, which was covalently attached to carrier protein bovine serum albumin via the UDP nucleotide. Serum raised using this antigen showed specificity for chemically immobilised peptidoglycan monomer containing (Gly)₅, using an ELISA immunoassay. ELISA assays using 0.1 or 1.0 μg samples of cell walls prepared from two MRSA strains and one penicillin-sensitive S. aureus strain, and from three other bacteria, showed the highest response against cell walls containing (Gly)₅, with a particularly high response against cell walls from one MRSA strain. Competition assays to investigate antibody selectivity demonstrated that the antibody response could be most effectively antagonised using ligands containing (Gly)₅. These data demonstrate that it is possible to generate antibodies with high affinity and selectivity for the (Gly)₅ containing monomer in S. aureuspeptidoglycan, that could be used to develop an immunoassay for S. aureus.