Abstract:

[Abstract]   Objective   To study mechanisms of lipopolysaccharide (LPS) release from Acinetobacter baumannii (A.
baumannii) induced by biapenem (BIPM), meropenem (MEM) and levofloxacin (LVFX).  Methods   A. baumannii was exposed to different concentrations of BIPM, MEM, LVFX, and ceftazidime (CAZ) at different time points. The LPS release was measured by tachypleus amebocyte lysate (TAL) test. Quantities of bacteria exposing to0.5MIC antibiotics were measured.The morphology of bacteria treated with different antibiotics for7-hour was evaluated by light microscope.  Results   The LPS releases of A. baumannii treated with four kinds of antibiotics were significantly less than those of control group. In the later period, LPS releases of A. baumannii exposed to the high concentration of antibiotics tended to smooth. The cell quantities of bacteria were significantly lower in treatment group than that of control group. The cells of A. baumannii treated with CAZ and LVFX showed long filamentous shape. The bacteria exposed to MEM and BIPM showed obviously globular. At the same time, some bacterial cells were induced to lysis rapidly by BIPM.  Conclusion   The level of LPS release is influenced by kinds of antibiotics, concentration and incubation period. All kinds of antibiotics could induce morphological changes of A. baumannii, which may be related to the different mechanisms that bacteria induce the different levels of LPS release.

Key words: ceftazidime, beta-lactams, ofloxacin, acinetobacter baumannii, endotoxins, biapenem, meropenem