Researchers found that the human antimicrobial peptide LL‑37 and its shorter versions can kill the parasite that causes trichomoniasis, even strains that resist the usual drug metronidazole. The smallest piece, KR‑20, worked best, and mixing low amounts of these peptides with metronidazole made the drug work better against both sensitive and resistant parasites. This is early‑stage lab work, so it isn’t a ready‑to‑use treatment yet, but it hints that peptide‑based supplements could boost standard therapy in the future.

The parasite Trichomonas vaginalis is the aetiologic agent of trichomoniasis, the most common non-viral sexually transmitted disease worldwide. This infection often remains asymptomatic and is related to several health complications. The traditional treatment for trichomoniasis uses drugs of the 5-nitroimidazole family, such as metronidazole; however, scientific reports indicate an increasing number of drug-resistant strains. Antimicrobial peptides could be an alternative or complementary treatment. In this sense, one attractive candidate is the human cathelicidin, being LL-37 its active form. LL-37 possesses microbicidal activity against many microorganisms such as bacteria, Candida albicans, and Entamoeba histolytica. Shorter sequences derived from this peptide, such as KR-20, FK-13 and KR-12, have been shown to possess a higher microbicidal effect than LL-37. In this study, we determined the activity of LL-37 and its derivatives against T. vaginalis, which was unknown. The results showed that the four peptides (LL-37, KR-20, FK-13-NH₂ and KR-12) decreased the viability of T. vaginalis on a 5-nitroimidazole-sensitive and a 5-nitroimidazole-resistant strain; however, KR-20 was the most effective peptide, followed by FK-13-NH₂. Low concentrations of all peptides showed a better effect when combined with metronidazole in the sensitive and resistant T. vaginalis strains. These results are promising for potential future therapeutic uses.