Tolerant response of Streptococcus sanguis to beta-lactams and other cell wall inhibitors.

In contrast to group A streptococci or Streptococcus pneumoniae, cells of Streptococcus sanguis (group H) do not exhibit the irreversible effects of penicillin treatment, such as loss of viability or lysis. On the other hand, the same bacteria show typical effects of penicillin, such as morphological alterations, reduction in the rate of cell wall synthesis, and secretion of murein and lipoteichoic acid polymers into the medium. A novel effect of cell wall inhibitors was also noted: treatment with beta-lactams or with fosfomycin, d-cycloserine, or beta-halogeno-d-alanine caused the release of substantial amounts of glycerol lipids into the growth medium. The antibiotic "tolerance" of S. sanguis is interpreted in terms of the hypothesis that the activity of bacterial murein hydrolases is essential for the irreversible effects of cell wall inhibitors.