The Carboxyl Terminus of Peptidoglycan Stem Peptides Is a Determinant for Methicillin Resistance in Staphylococcus aureus

Abstract

ABSTRACT A mecA -containing Staphylococcus aureus strain was grown in the presence of high concentrations of d -serine, d -threonine, and d -phenylalanine. These growth conditions resulted in the replacement of the carboxyl-terminal (fifth) d -alanine residue of peptidoglycan stem peptides with the d- amino acid present in the growth medium and a reduced ability to grow in the presence of methicillin. The most dramatic effect was seen with d -serine. With 32 mM d -serine, strains that had been able to grow in the presence of 800 μg of methicillin per ml were only able to grow in the presence of less than 50 μg/ml. The results also suggest that in S. aureus vancomycin resistance mediated through the incorporation of precursors not terminating in d -alanyl- d -alanine would be mutually exclusive with expression of mecA -mediated methicillin resistance.