EFFECT OF EXOGENOUS GLYCINE ON PEPTIDOGLYCAN COMPOSITION AND RESISTANCE IN A METHICILLIN-RESISTANT STAPHYLOCOCCUS-AUREUS STRAIN

A highly homogeneously methicillin-resistant Staphylococcus aureus str ain was grown in the presence of various concentrations of exogenous g lycine. Increasing concentrations of glycine in the medium resulted in a decrease in methicillin resistance and the appearance of a heteroge neous resistance phenotype. Parallel to the gradual changes in resista nce was an alteration in the muropeptide composition of peptidoglycan. Increasing concentrations of glycine in the medium resulted in peptid oglycan in which muropeptides with a D-alanyl-D-alanine terminus were replaced with D-alanyl-glycine-terminating muropeptides. The disappear ance of D-alanyl-D-alanine-terminating muropeptides in peptidoglycan a nd the concomitant decrease in resistance indicate a central role for D-alanyl-D-alanine-terminating precursors in methicillin resistance.