Peptide Basics
Antimicrobial Peptides: What They Are, How They Work and Examples
Antimicrobial peptides are small, mostly positively charged peptides that animals, insects and plants use as an early defence against microbes, mainly by damaging the microbe’s membrane. This page sets out how the U.S. National Library of Medicine defines them, human examples (the defensins, LL-37 and the histatins) with their lengths from UniProt, how they attack a membrane, the antimicrobial peptides found in frogs and bacteria, including the food preservative nisin, and which peptide antibiotics FDA has approved. FDA’s approvals database lists no human defence peptide as the active ingredient of any approved medicine.
What antimicrobial peptides are
MeSH defines antimicrobial peptides as small peptides that play an important role in early innate and induced defences against invading microbes, and adds that most have a positive overall charge, so they are referred to as cationic antimicrobial peptides. In animals, MeSH places them on mucosal surfaces, inside the granules of phagocytes (the white blood cells that swallow microbes) and on the surface of the body; they are also found in insects and plants. The group includes the defensins, protegrins, tachyplesins and thionins.
They belong to the innate immune system, the body’s inborn defences. Our page on types of peptides places them among the peptides classified by function.
How they attack a microbe
MeSH records the mechanism for the cationic peptides: they displace divalent cations from the phosphate groups of membrane lipids, which disrupts the membrane. For the cathelicidins it states that they kill non-viral pathogens by forming pores in membranes, and for the magainins from frog skin that they kill bacteria by permeabilising cell membranes without significant toxicity to mammalian cells.
Killing is not their only role. MeSH links the defensins to host defence against infection and also to inflammation, wound repair and acquired immunity, which is why the research literature also calls many of them host-defence peptides.
Sources: NLM MeSH descriptors D000089882, D023181, D054804, D054806 and D023082. Read 1 November 2026.
Human antimicrobial peptides
Each is cut from a longer precursor that starts with a signal peptide. Alpha-defensins are found, according to MeSH, in the granules of neutrophils and in the Paneth cells of the intestine; beta-defensins mainly in epithelial cells.
| Peptide | Family (MeSH) | Amino acids | Note |
|---|---|---|---|
| Histatin-3 | Histatins | 32 | A histidine-rich salivary peptide; MeSH records histatins as antibacterial and antifungal. |
| HNP-1 (neutrophil defensin 1) | Alpha-defensins | 30 | Stored in neutrophil granules; three disulfide bonds hold it together. |
| Beta-defensin 1 (hBD-1) | Beta-defensins | 36 | Made mainly by epithelial cells; three disulfide bonds. |
| Beta-defensin 2 (hBD-2) | Beta-defensins | 41 | A second epithelial beta-defensin; three disulfide bonds. |
| LL-37 | Cathelicidins | 37 | The last 37 amino acids of the 170-amino-acid cathelicidin precursor. |
LL-37 in detail. UniProt’s cathelicidin record (P49913) lists a 170-amino-acid precursor: a 30-amino-acid signal peptide, a 101-amino-acid cathelin-like domain, and the antimicrobial end, from which LL-37 (amino acids 134 to 170) and a slightly longer form, FALL-39, are cut, along with shorter fragments such as LL-29, LL-23 and KR-20. MeSH describes cathelicidins as made first as preproproteins and then cleaved, with a highly conserved cathelin-like front end and a more variable antimicrobial end. Our LL-37 guide covers its research history and regulatory status.
Sources: UniProt P15516, P59665, P60022, O15263 and P49913; NLM MeSH descriptors D054808, D023084, D023083 and D054804. Read 1 November 2026.
Beyond humans: frogs, bacteria and food
- Magainins were discovered in the skin of the African clawed frog, Xenopus laevis, according to MeSH.
- Bacteriocins are substances made by particular strains of bacteria that are lethal to other strains of the same or related species (MeSH).
- Nisin is one of them: a 34-amino-acid peptide from Lactococcus lactis whose ring-shaped lanthionine cross-links, listed in UniProt, make it a lantibiotic. MeSH notes its use as a preservative in canned fruit, vegetables and cheese, and under 21 CFR 184.1538 nisin preparation is generally recognised as safe in the United States to inhibit the outgrowth of Clostridium botulinum spores and toxin formation in pasteurised cheese spreads.
Sources: NLM MeSH descriptors D054806, D001430 and D009561; UniProt P13068; eCFR 21 CFR 184.1538. Read 1 November 2026.
Peptide antibiotics that are approved medicines
Several approved antibiotics are peptides or peptide-based molecules made by bacteria. MeSH describes polymyxins as lipopeptides from Bacillus polymyxa that act on the cell membrane by detergent action and may cause neuromuscular and kidney damage; bacitracin as a mixture of cyclic peptides from Bacillus subtilis used on the skin; gramicidin as peptides from Bacillus brevis; and vancomycin as a glycopeptide that blocks assembly of the bacterial cell wall. Some approved examples, in order of first U.S. approval:
| Antibiotic | U.S. brand | First approved | What it is |
|---|---|---|---|
| Colistin, given as colistimethate | Coly-Mycin M | 1970 | Cyclic polypeptide from Bacillus colistinus (polymyxins E1 and E2); acts like a detergent on bacterial membranes. |
| Daptomycin | Cubicin | 2003 | Cyclic lipopeptide made by fermentation of Streptomyces roseosporus; active against Gram-positive bacteria. |
| Telavancin | Vibativ | 2009 | Lipoglycopeptide; a synthetic derivative of vancomycin. |
| Dalbavancin | Dalvance | 2014 | Lipoglycopeptide made from a fermentation product of Nonomuraea species. |
No human defence peptide is among them. A search of Drugs@FDA on 1 November 2026 found no product with LL-37, a cathelicidin, a defensin, a histatin or a magainin as its active ingredient.
Sources: Drugs@FDA original approval dates (Coly-Mycin M NDA050108, Cubicin NDA021572, Vibativ NDA022110 and Dalvance NDA021883) and active-ingredient search; U.S. labels via openFDA for daptomycin, Dalvance and Vibativ; NLM MeSH descriptors D011113, D003091, D017576, D001414, D006096 and D014640. Read 1 November 2026.
Antimicrobial peptides sold for research
LL-37 is sold as a research compound, and KPV, a three-amino-acid fragment of the hormone alpha-MSH, is often listed next to it. KPV is mainly described as anti-inflammatory; one 2000 laboratory study reported that alpha-MSH peptides including KPV also inhibited Staphylococcus aureus and Candida albicans in culture. A compound sold for research use only is labelled not for human use. Our pages on what research peptides are and whether peptides are legal set out what regulators have said.
Medibact does not manufacture or sell peptides. We supply USP-grade bacteriostatic water, made in the USA, for research use only, and publish reference material like this page.
Where this sits in the rest of the reference
FAQ
What are antimicrobial peptides?
Antimicrobial peptides, or AMPs, are small peptides that the body uses as an early line of defence against microbes. The U.S. National Library of Medicine’s MeSH vocabulary defines them as small peptides that play an important role in early innate and induced defences against invading microbes, and notes that most carry a positive overall charge, which is why they are also called cationic antimicrobial peptides. They are found in animals, insects and plants.
How do antimicrobial peptides work?
Mainly by damaging the microbe’s membrane. MeSH records that cationic antimicrobial peptides displace divalent cations from the phosphate groups of membrane lipids, disrupting the membrane, and that cathelicidins kill non-viral pathogens by forming pores in membranes. Defensins are also linked in MeSH to inflammation, wound repair and acquired immunity, so some of these peptides do more than kill microbes.
What are examples of antimicrobial peptides in humans?
Examples include the defensins, LL-37 and the histatins. Alpha-defensins such as HNP-1 (30 amino acids) are stored in neutrophils and in Paneth cells of the gut; beta-defensins such as hBD-1 (36) and hBD-2 (41) are made mainly by epithelial cells; LL-37 (37) is cut from the cathelicidin precursor; histatins are histidine-rich peptides in saliva. Lengths are from UniProt.
What is LL-37?
LL-37 is the human cathelicidin antimicrobial peptide. UniProt lists it as amino acids 134 to 170 of a 170-amino-acid precursor that also carries a 30-amino-acid signal peptide and a 101-amino-acid cathelin-like domain; the name comes from its first two amino acids, two leucines, and its length. UniProt also lists shorter fragments cut from the same stretch, such as LL-29, LL-23 and KR-20. Our LL-37 guide covers its research history and regulatory status.
Are antibiotics peptides?
Some are. Colistin and polymyxin B, daptomycin, bacitracin, gramicidin and the glycopeptides such as vancomycin are peptide or peptide-based antibiotics made by bacteria. MeSH describes polymyxins as lipopeptides that act on the cell membrane by detergent action and may cause neuromuscular and kidney damage, and daptomycin as a cyclic lipopeptide.
Is nisin an antimicrobial peptide?
Yes. Nisin is a 34-amino-acid peptide made by the bacterium Lactococcus lactis, with ring-shaped cross-links called lanthionines, which makes it a lantibiotic. Under 21 CFR 184.1538 nisin preparation is generally recognised as safe in the United States as an antimicrobial agent to inhibit the outgrowth of Clostridium botulinum spores and toxin formation in pasteurised cheese spreads.
Are any human antimicrobial peptides approved as medicines?
Not in the United States. A search of Drugs@FDA on 1 November 2026 found no product with LL-37, a cathelicidin, a defensin, a histatin or a magainin as its active ingredient. The approved peptide antibiotics, such as daptomycin and colistimethate, come from bacteria, not from the human defence peptides.
Is KPV an antimicrobial peptide?
Not in the usual sense. KPV is the tripeptide Lys-Pro-Val from the end of alpha-MSH, a melanocortin hormone, and is mainly described as anti-inflammatory. One 2000 laboratory study (Cutuli and colleagues) also reported that alpha-MSH peptides including KPV inhibited Staphylococcus aureus and Candida albicans in culture. Our KPV guide sets out that research and its limits.
Is this medical advice?
No. This page explains what antimicrobial peptides are, from public scientific and regulatory records. It gives no dose, schedule, protocol or recommendation, and peptides sold for research are labelled research use only, not for human use. Medibact supplies USP-grade bacteriostatic water, made in the USA, and does not manufacture or sell peptides.
References: NLM MeSH descriptors D000089882, D023181, D023082, D023084, D023083, D054804, D054808, D054806, D001430, D009561, D011113, D003091, D017576, D006096, D001414 and D014640; UniProt P49913, P59665, P60022, O15263, P15516 and P13068; eCFR 21 CFR 184.1538; Drugs@FDA and openFDA labels. Read 1 November 2026.
Educational use only — not medical advice. This guide summarizes information reported in published research and community practice for educational purposes. It is not medical advice and not a recommendation to use any compound. Any doses, schedules, or combinations shown are examples of what has been reported, not instructions for you. Many peptides described here are research compounds that are not FDA-approved for the uses discussed and may be investigational or restricted. Effects, risks, and legal status vary; individual needs and results vary. Consult a qualified, licensed healthcare professional before making any decision. Do not use this content to diagnose, treat, or dose yourself.