AIMTo investigate the inhibitory effect of egg white lysozyme (LZM) on ceftazidime (CFT)-induced release of endotoxin from Pseudomonas aeruginosa.

METHODSP. aeruginosa PAO1 was inoculated in nutrition broth or diluted rabbit blood free of antibiotics in the presence or absence of LZM and incubated at 37 degrees C on a water bath shaker. beta-Lactam antibiotic, CFT, was added to cultures at 3.5 h (nutrition broth culture) or 5 h (diluted rabbit blood culture) after inoculation. After 3 h of CFT treatment, the supernatants from different bacterial cultures were prepared by centrifuge and the concentrations of endotoxin in the supernatants were measured. The bacterial supernatants were also added to a murine macrophage cell line RAW 264.7 or intravenously injected into carrageenin-sensitized mice. Tumor necrosis factor-alpha (TNF alpha) and nitric oxide (NO) concentrations in RAW 264.7 supernatants or in mouse sera were tested.

RESULTSCFT treatment alone obviously inhibited the growth of P. aeruginosa PAO1 accompanied by strong and rapid bacteriolysis and released relatively high concentration of endotoxin from bacteria both in nutrition broth and in diluted rabbit blood cultures. The bacterial supernatant from CFT treatment alone yielded high concentrations of TNF alpha both in RAW 264.7 cells and in mice and high level of NO in RAW 264.7 cells. Treatment with the combination of LZM and CFT evidently blocked the lysis of bacteria and reduced the release of endotoxin without decreasing bactericidal activity of CFT. TNF alpha and NO productivity of the supernatants prepared from the LZM/CFT combinative treated bacterial cultures were significantly decreased both in RAW 264.7 cells and in mice indicating that the inflammatory activity was reduced.

CONCLUSIONLZM can effectively prevent CFT-induced bacteriolysis, endotoxin release and subsequent proinflammatory factor production but without decreasing bactericidal activity of CFT, resulting in the disassociation of bactericidal activity and bacteriolysis. Thus, LZM might be important for preventing endotoxemia in Gram-negative sepsis with the treatment of antibiotics.