ABSTRACT
Objective To study the antimicrobial activity of chemically synthesized Musca domes-tica cecropin-4 (mdCec4) against Acinetobacter baumannii. Methods Minimum inhibitory concentration (MIC) and minimum bactericidal concentration(MBC) of mdCec4 against Acinetobacter baumannii were de-tected by microdilution method. Dynamic time-kill curve was monitored by microplate reader. Effects of dif-ferent influencing factors,such as NaCl,trypsin and pH value,on the antimicrobial activity of mdCec4 were assessed. The ultrastructure of Acinetobacter baumannii exposed to the MIC of mdCec4 was observed under scanning electron microscope (SEM). Results The MIC and MBC of mdCec4 against Acinetobacter bau-mannii were 4 μg/ml and 8 μg/ml,respectively. The dynamic time-kill curve revealed that mdCec4 had a high antimicrobial activity within 24 hours. The antimicrobial activity of mdCec4 was not affected by NaCl concentration ranged from 0 to 200 mmol/L, but could be inhibited by trypsin at a concentration of 1.0 mg/ml. Among Tris-HCl buffers with different pH values (6.5, 7.5, 8.8), the optimum condition for mdCec4 was pH8.8. Results of SEM showed that the degree of bacterial cell injury was positively correlated with exposing time. Conclusion This study shows that the newly discovered mdCec4 has a better antimicro-bial activity against Acinetobacter baumannii as it can eliminate Acinetobacter baumannii within a short period of time and its antimicrobial ability can last more than 24 hours. Moreover,mdCec4 has the characteristic of good stability in conditions of different concentrations of NaCl and Trypsin as well as various pH values. SEM observation shows that the MIC of mdCec4 can destroy the integrity of bacterial membrane resulting in a re-lease of a large number of cell contents, which finally lead to the death of Acinetobacter baumannii. This study provides references for further study of the antimicrobial mechanism of mdCec4 against Acinetobacter baumannii.