Preliminary Study On The Effect Of Synthetic Antimicrobial Peptides Against Escherichia Coli Biofilm

Objective: To study the effect of synthetic antimicrobial peptides using only and with gentamicin against Escherichia coli biofilm. Methods: The MIC and MBC of antimicrobial peptides and gentamicin against Escherichia coli was measured respectively. The test tube method was used to establish the model of 24h Escherichia coli biofilm with 28 8×8 millimeter cover slips. The planktonic Escherichia coli were washed out from the cover slips with sterile Phosphate buffered saline repeatedly. The samples were randomly divided into four groups: group A, by adding 4×MIC antimicrobial peptides to the samples, group B ,by adding 1×MIC gentamicin to the samples, group C, by adding 4×MIC antimicrobial peptides and 1×MIC gentamicin to the samples, group D, by adding phosphate buffered saline to the samples as a control. All the samples were put in the incubator for 24h. The vestigial drugs were washed out from the cover slips with sterile Phosphate buffered saline repeatedly after 24h. The viable bacteria in the biofilm were rinsed off from the cover slips by the ultrasonic cleaner. The rinsed bacterial liquid was blended adequately with oscillator. The viable bacteria in rinsed bacterial liquid were counted following the method of colony count. The different changes in the biofilm were compared between the treated groups and the control group with scanning electron microscope. Results: The MIC and MBC of antimicrobial peptides against Escherichia coli were 16μg/ml and 128μg/ml,while the MIC and MBC of gentamicin were 1μg/ml and 8μg/ml. The viable bacteria in group C were significantly decreased compared with the other three groups (P<0.05). Compared with group D,the viable bacteria were decreased in group A and group B (P<0.05) .While there was no difference between group A and group B(P>0.05). In the graph of scanning electron microscope the integrity of the Escherichia coli cell membrane was destroyed in group A and C, while there was no analogic change in group D. Conclusion: The results suggest that the killing effect of antimicrobial peptides against Escherichia coli biofilm is poor. While the killing effect of combination of antimicrobial peptides with gentamicin is significantly increased, 10 000-30 000 times better than the killing effect of using alone.