The potential use of secondary metabolites from Bacillus amyloliquefaciens to control Acinetobacter baumannii

Background and Objective : Acinetobacter baumannii  is an important cause of hospital-derived infection or nosocomial infections in many hospitals. The bacterium has an ability to survive for a long time on common surfaces including medical equipments and drug resistant isolates have been increasingly reported. Bacillusamyloliquefaciens N3-8 was isolated from soil. The secondary metabolites that were produced from this organism showed inhibition againstseveral pathogens including A. baumannii . This study aimed toobserve the range of inhibition and to set a model investigating the ability of crude proteinsproduced from B. amyloliquefaciens inkilling A. baumannii on plastic surface. Material and Methods: The inhibition activity of crude proteins from B. amyloliquefaciens N3-8 was observed against 28isolates of A. baumannii by agar well diffusion. Imipenem, the drug of choice, was used as a positive control. The efficiency of crude proteinsfrom theN3-8 to kill or prevent A. baumannii contamination was done on plastic surface and observed by colony count and streak plate methods using A. baumannii N5, which is a drug resistant isolate.Chlorhexidine of 1.5% was used as a positive control. Results: Thecrude proteins could inhibit 71% (20/28) while imipenem could inhibit only 21% (6/28) of total A. baumannii isolates. Seven isolates showed no inhibition by both compounds, 15 isolates were inhibited by crude proteins but not imipenem, 5 were inhibited by both compounds and 1 isolate was inhibited by imipenem but not the crude proteins. Crude protein at concentrations of1, 2, 4, 8, 16 and 32 mg/ml that spread overthe 5x10 6 CFU/ml of N5 or the other way round could completely kill the bacterium. When N5 was applied before and after the crude proteins, the concentrations of2, 4, 8, 16 and 32 mg/ml could completely kill the N5 similar to 1.5% chlorhexidine. Conclusion: These may be no advantage to use the crude proteins from B.amyloliquefaciens N3 - 8 for antiseptic purpose but they were superior to imipenem in killing the majority of A. baumannii isolates. Further purification and characterization may lead to the discovery of a new drug for treatment of A. baumannii .