Effect of elevated atmospheric pressure on penicillin binding by Staphylococcus aureus and Streptococcus pyogenes.

A gas pressure of 68 atm, elicited by helium-oxygen gas mixtures, reduced the susceptibility to penicillin of Staphylococcus aureus but not of Streptococcus pyogenes. The elevated pressure also caused a reduction in the binding of (14)C-penicillin to S. aureus, but not to S. pyogenes. When these studies were extended to glycine incorporation, it was shown that, even without penicillin, pressurization reduced glycine incorporation into the cell wall of S. aureus. Incorporation into other cellular components was not altered by pressurization. Cells grown in a pressurized environment were slightly more susceptible than those grown at 1 atm to rapid change in osmotic pressure. In the presence of penicillin, glycine incorporation into the cell wall was reduced to the same low level at 68 atm and at 1 atm. These results suggest that pressurization renders S. aureus less susceptible to penicillin because it reduces the enzymatic activity of the binding component on the cell, a penicillin-sensitive transpeptidase.