Mechanism of killing of pneumococci by lysozyme

J Infect Dis. 1991 Sep;164(3):527-32. doi: 10.1093/infdis/164.3.527.


Lysozyme is abundant in respiratory secretions and may play a role in lung host defenses. Mechanisms by which lysozyme killed Streptococcus pneumoniae, an important respiratory pathogen, were studied. Lysozyme caused optical clearing of pneumococcal suspensions and released fragments containing [3H]choline from their cell walls. Electron micrographs revealed wide-spread cell wall destruction and bacteriolysis. Breakdown of the cell wall appeared to be mediated mostly by the major pneumococcal autolysin, N-acetylmuramoyl-L-alanine amidase, because it was blocked by phosphorylcholine, a specific inhibitor of amidase, or by substitution of ethanolamine for choline in the cell wall. Blockade of amidase did not greatly increase survival of lysozyme-treated pneumococci on blood agar. Pneumococci in which amidase was blocked appeared intact immediately after treatment with lysozyme, but when they were reincubated at 37 degrees C in fresh culture medium they swelled and lysed. Thus, widespread triggering of the major pneumococcal autolysin is not essential for the bactericidal effect of lysozyme.

Publication types

  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Bacteriolysis
  • Cell Wall / metabolism
  • Cell Wall / ultrastructure
  • Microscopy, Electron
  • Muramidase / metabolism*
  • N-Acetylmuramoyl-L-alanine Amidase / metabolism
  • Phosphorylcholine / metabolism
  • Streptococcus pneumoniae / enzymology*
  • Streptococcus pneumoniae / ultrastructure


  • Phosphorylcholine
  • Muramidase
  • N-Acetylmuramoyl-L-alanine Amidase