The Efficacy of the Antimicrobial Peptide Melittin and the Enzyme DNase I Against E. coli Biofilms

Abstract

Biofilms are aggregations of bacteria that often cause nosocomial infections and are tolerant to antibiotic treatments due to a variety of factors, including the physical barrier of their matrix. One field of treatment that has been explored is the use of antimicrobial peptides, like melittin. Melittin has been demonstrated to have antimicrobial effects on bacteria in both a biofilm and a planktonic state. Its required concentration to affect biofilms, however, is too high to be applicable in clinical settings. One potential way to increase efficacy is to use a compound like DNase I that degrades the matrix and thereby increases the penetration of melittin into the biofilm. I investigated whether DNase I would enhance the efficacy of melittin in relatively low concentrations that could be clinically viable. Melittin and DNase I were applied to E. coli biofilms in 24-well plates, both individually and in combination; biofilm density was measured at two time-points afterwards, using a crystal violet staining assay. The results showed DNase I was the most effective treatment. Surprisingly, none of the melittin treatments were statistically significant. A second experiment investigated variation among 11 bioreplicates and found that there was approximately 5-fold variation in response to treatment with DNase I. Given these promising results, further study on DNase I should be conducted.\n\nImportanceThis work is important as it is crucial to have as many viable treatment options as possible for biofilm infections. Biofilm infections are common and many of our standard antibiotic options are simply not effective against them. According to the NIH, 65% of microbial infections and 80% of chronic infections are associated with biofilms, costing the United States millions of dollars each year (Jamal et al., 2018). Every avenue that could potentially further efforts to increase the efficacy and practicality of treatment options should be explored. Antimicrobial peptides are one of the most promising fields for biofilm treatment, and this study further investigates the potential for treatment that they hold.