Effect of MUC7 peptides on the growth of bacteria and on Streptococcus mutans biofilm

Objectives: To investigate the susceptibility of selected bacteria as well as Streptococcus mutans biofilm to MUC7 peptides and compare the activities with those of other known antimicrobial peptides. Methods: MIC and MBC of peptides for S. mutans, Escherichia coli, Streptococcus gordonii, Actinobacillus actinomycetemcomitans, Porphyromonas gingivalis and Pseudomonas aeruginosa were determined using the microdilution method. For S. mutans, the effects of the peptides on the kinetics of growth inhibition, time-killing, and on biofilm formation and reduction were also examined. For biofilm studies, polystyrene microtitre plates, Calgary Biofilm Device (CBD) and hydroxylapatite (HA) discs, along with Crystal Violet and Alamar Blue dyes, and/or EM observations, were employed. Results: S. mutans was the most susceptible to all peptides tested (MICs of 9.4-25.0 mu M), compared with the other species (MICs of 3.1 -> 100 mu M). MUC7 peptides (except MUC7-12-mer-L4) exerted 2-fold higher activity against S. mutans than Hsn5-12-mer and magainin-II, and faster killing of S. mutans than Hsn5-12-mer. The MUC7 peptides also had an effect on S. mutans biofilm. On the polystyrene plates, they suppressed the biofilm formation, with MBIC50 of 6.25-12.5 mu M, and reduced the 1 day developed biofilm in a batch culture, with MBRC50 of 25-50 mu M. On the CBD pegs, the viabilities of the biofilm were suppressed by > 95% in the presence of MUC7 peptides at 4x MIC (50 mu M). One day developed biofilm viabilities were inhibited by 49-75%. On HA, the formation of biofilm (as observed by EM) was also considerably reduced. Conclusions: MUC7 peptides present somewhat preferential antimicrobial activity against S. mutans. They also have an effect on in vitro formation and reduction of the preformed S. mutans biofilm.