Antimicrobial activity of Substance P and Neuropeptide Y against laboratory strains of bacteria and oral microorganisms

Infection and inflammation of mucosal tissue may induce the production of neuropeptides, specifically Substance P and Neuropeptide Y. Since these neuropeptides are similar to antimicrobial peptides in their amino acid composition, amphipathic design, cationic charge, and size, we wanted to determine if they had antimicrobial activity against a panel of common bacteria and oral microorganisms using the radial diffusion assay. Neuropeptide Y and Substance P had antimicrobial activity against E. coli (MIC 20.6 ± 5.5 μg/ml SEM and 71.5 ± 15 SEM μg/ml, respectively), but did not have activity against laboratory strains of Staphylococcus aureus, Pseudomonas aeruginosa, Klebsiella pneumoniae, and Serratia marcescens (MIC > 500 μg/ml) nor oral strains of Streptococcus mutans, Candida albicans, and Actinobacillus actinomycetemcomitans (MIC > 500 μg/ml). While Substance P and Neuropeptide Y did not have direct antimicrobial activity against the microorganisms tested, they still may stimulate local epithelial cells to produce other innate immune factors like defensins and cathelicidins. However, this remains to be determined.