The paper shows that the natural antimicrobial peptide LL‑37 found in saliva is too low to kill the cavity‑causing bacteria Streptococcus mutans, but adding synthetic LL‑37 at high micromolar levels (8‑10 µM) can kill S. mutans while leaving the friendly S. gordonii untouched. However, achieving such concentrations in the mouth with everyday products is difficult, so the finding is more of a proof‑of‑concept than a ready‑to‑use hack.

The antimicrobial peptide hCAP18/LL-37 is detected in desquamated epithelial cells of human whole saliva, but the functional importance of this pool of hCAP18/LL-37 is not understood. Here, we assess the impact of homogenates of desquamated oral epithelial cells and exogenous, synthetic LL-37 on two oral bacteria: <i>S. mutans</i> and <i>S. gordonii</i>. Desquamated epithelial cells of unstimulated whole saliva were isolated and cellular and extracellular levels of hCAP18/LL-37 analyzed by ELISA. Bacterial viability was determined by BacLight Live/Dead staining and confocal laser scanning microscopy. Desquamated oral epithelial cells harboured hCAP18/LL-37, and they spontaneously released/leaked the peptide to their medium. Exogenous, synthetic LL-37 showed cytotoxic activity against <i>S. mutans</i> but not <i>S gordonii</i>, suggesting that LL-37 acts differentially on these two types of oral bacteria. Homogenates of desquamated oral epithelial cells had no effect on <i>S. mutans</i> viability. Treatment with exogenous, synthetic LL-37 (8 and 10&#x2009;&#x3bc;M) reduced <i>S. mutans</i> viability, whereas lower concentrations (0.1 and 1&#x2009;&#xb5;M) of the peptide lacked effect. Desquamated oral epithelial cells contain hCAP18/LL-37, but their cellular levels of hCAP18/LL-37 are too low to affect <i>S. mutans</i> viability, whereas exogenous, synthetic LL-37 has a strong effect on these bacteria.