This 2023 review explored a naturally produced antimicrobial:

“This review focuses on the role of abundant hypothiocyanous acid (HOSCN), a potent oxidant that kills bacteria but is non-toxic to human cells. Produced from thiocyanate (SCN⁻) and hydrogen peroxide (H₂O₂) in a variety of body sites by peroxidase enzymes, HOSCN has been explored as an agent of food preservation, pathogen killing, and even improved toothpaste.

Lactoperoxidase (LPO) is considered the main producer of HOSCN, and is secreted in saliva, tears, breastmilk, and lacrima of mammals. LPO regulates the oral microbiome and keeps breastmilk free of pathogens during the first few weeks after delivery. LPO has long been understood to play a role in prevention of dental caries.

Thiocyanate is mostly acquired from diet. Many food plants contain glucosinolates – precursors to isothiocyanates – found in vegetables of order Brassicales (broccoli, cabbages, turnips, mustard, horseradish, etc.).

HOSCN is likely to exist at substantial concentrations in the oral cavity and the respiratory tract, and is probably present under any inflammatory circumstances. Oxidative damage caused by HOSCN is largely reversible, since HOSCN cannot oxidize thiols to sulfinic or sulfonic acid.

The study of bacterial HOSCN stress response is in its infancy. Results summarized above suggest overlaps with both ROS and RCS responses, particularly in the areas of redox homeostasis (e.g., glutathione metabolism), cysteine metabolism, and prevention of protein aggregation, but considerable work needs to be done to more fully characterize this response.”

https://onlinelibrary.wiley.com/doi/10.1111/mmi.15025 “Hypothiocyanite and host–microbe interactions”