Light and scanning-beam electron microscopy of wall-defective Staphylococcus aureus induced by lysostaphin

The serial morphological changes of Staphylococcus aureus after exposure to lysostaphin (one unit per ml) in hypertonic culture medium containing 5% NaCl were studied over an 8-hr period at 37 C. S. aureus stained gram-negative almost instantaneously upon contact with lysostaphin. Many cells were lysed, but wall-defective staphylococci with corrugated surface were detected as early as 5 min by use of scanning-beam electron microscopy. Wall-defective staphylococci enlarged progressively with increasing periods of incubation. The absorbance of the lysostaphin-treated culture decreased significantly by 2 min, remained stationary for 2 hr, and then progressively increased. The number of vegetative colony-forming units decreased progressively with increasing periods of incubation, whereas the number of L-colony-forming units remained the same.