Suppression of lytic effect of beta lactams on Escherichia coli and other bacteria.

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Abstract
Growth of E. coli at pH 5 protected the bacteria against the lytic effect of .beta.-lactam antibiotics typically observed when the cells are grown at pH 7 or 7.5, i.e., the pH values routinely used in laboratory experiments. The typical effects of .beta.-lactam antibiotics on cellular shape and elongation and cell division appeared to be similar in cultures grown under neutral and acid pH conditions. The pH-dependent antibiotic tolerance can also be demonstrated with pneumococci, staphylococci, streptococci and Bacillus subtilis. The mechanism of the pH-dependent antibiotic tolerance may involve either the production of a more stable plasma membrane or the suppression of the activity of a murein hydrolase(s) that catalyzes the antibiotic-induced lysis; at least a fraction of these enzyme molecules may be localized at the cell surface and be accessible to experimental manipulation.