[An experimental study of the LPS release from gram-negative bacteria induced by antibiotics (Part two)].

Objective: To explore the effects of different beta-lactam antibiotics on the inducing of LPS release from gram-negative bacteria and on the protection of infected animals.

Methods: Wistar rats were employed as the model and were inflicted by 30% TBSA III degree scalding and sepsis caused by PA103. The rats were randomly divided into 3 groups, i.e. simple antibiotic treatment group (A), treatment after sensitization with galactosamine (GalN) group (G) and treatment after blocking with carrageenan (CGN) group (C). The rats were injected intra-peritoneally with imipenem (IMP, 5 mg) and ceftazidime (CTZ, 10 mg) for single time, respectively. Same amount of aseptic normal saline was injected in the control group, and GalN (50 mg) was added in G and CGN (1 mg) in C groups. The blood bacterial concentration and plasma LPS levels were determined at different time points after the treatment by antibiotics. The mortality was observed in G and C groups at 10 days after treatment.

Results: The blood bacterial amount could be decreased by both IMP and CTZ evidently. Large amounts of LPS released from PA103 could be induced by IMP and CTZ during their bactericidal process. But the plasma LPS level in rats treated by CTZ was markedly higher than that by IMP (P < 0.05 approximately 0.01). The mortality in G group treated by CTZ was much higher than that by IMP (P < 0.05). Nevertheless, the mortality in C groups was the same no matter CTZ or IMP was applied (P < 0.05).

Conclusion: There was no difference of the bactericidal power between IMP and CTZ. But CTZ was more powerful in inducing LPS release from bacteria than IMP. It was implied by the difference between these two antibiotics that IMP might be better choice in clinical application for burn infection due to its lower potential of inducing LPS release from the bacteria.