Table 1

Properties of bacteria producing either wild-type (WT) or mutant LLO proteins. Hemolytic units are expressed as the reciprocal of the dilution of bacterial culture supernatant required for 50% lysis of a 0.5% sheep red blood cell suspension as described (8). Escape from primary phagosomes of murine bone marrow–derived macrophages was determined by using indirect immunofluorescence to count the percentage of bacteria decorated with actin filaments 90 min after infection (8). Association with host actin indicates that the bacterium has reached the cytosol. Strain DP-L2161 contains a complete deletion of the LLO gene (8). LD50, 50% lethal doses (25).

StrainCytolysin synthesizedHemolytic unitsEscape from phagosome (%)LD50
pH 5.5pH 7.4
10403SWT LLO106111459  ±  62  ×  104
DP-L4042LLOΔ26151424355  ±  42  ×  108
DP-L4048LLOS44A,S48A,T51A 133015154  ±  43  ×  106
DP-L2161No cytolysin0002  ×  109