Antibacterial properties of human lysozyme toward Fusobacterium nucleatum Fev1

Human lysozyme in physiologic concentrations (17-50 micrograms/ml) had apparently no effects on growth rate and viability of exponentially growing Fusobacterium nucleatum Fev1 cells, but cells in the stationary phase were affected. When grown in the presence of active lysozyme about 70% of the cells in late exponential phase (24-h culture) were able to form colonies, compared to about 100% in the control culture. About 24 h later the colony forming abilities were about 5% and 20%, respectively. Addition of lysozyme to suspensions of cells taken from any growth phase did not lead to any significant decrease in turbidity, that is, no more than 10% decrease at 650 nm. Control cells treated with acridine orange fluoresced with a uniform bright orange color, while the lysozyme treated stationary phase cells fluoresced more faintly. Intracellular granules were more preponderant in the latter cells. When incubated with the hydrophobic probe 8-anilinonaphthalene-1-sulfonic acid (ANS), lysozyme exposed cells gave approximately 20% higher fluorescence intensity than the control cells. Changes in the ultrastructure of the lysozyme treated cells were best studied in the transmission electron microscope using ultrathin sectioned preparations. The peptidoglycan layer became disorganized and apparently dissolved and the ordered structure of the cell wall had disappeared in zones. The cells, however, still retained their form, and only a few per cent had lost their cellular content. This explains why the turbidity of the solution did not change significantly.