The Targeted Action of Natamycin
Natamycin, a polyene macrolide, exerts its effects primarily on yeasts and molds by targeting a crucial component of their cell membrane known as ergosterol. Unlike human cells, which use cholesterol, fungi rely on ergosterol for membrane integrity and function. This fundamental difference allows natamycin to selectively attack fungal pathogens while remaining largely non-toxic to human cells.
How Natamycin Kills Fungi
The mechanism is quite precise and involves a cascade of cellular events that ultimately lead to the fungus's demise.
- Binding to Ergosterol: Natamycin binds irreversibly to the ergosterol in the fungal cell membrane.
- Altered Membrane Permeability: This binding alters the permeability of the membrane, leading to the leakage of essential cellular components.
- Disruption of Cellular Transport: It inhibits amino acid and glucose transport proteins, further starving the cell of vital nutrients.
- Cell Death: The resulting loss of cellular constituents and disruption of transport eventually causes the fungal cell to die.
Why Natamycin Doesn't Affect Bacteria
Since bacteria lack ergosterol in their cell membranes, natamycin has no effect on them. This specificity is a significant advantage, particularly in applications like preserving fermented foods, where a bacterial ripening process is desired but mold growth is not.
Natamycin's Medical Uses and Low Absorption
In a medical context, natamycin is almost exclusively used topically, and its effects on the body are highly localized. The most common application is as ophthalmic drops (e.g., under the brand name Natacyn) to treat serious fungal eye infections such as blepharitis, conjunctivitis, and keratitis.
Medical Administration and Systemic Effects
Because it has very poor water solubility and is not readily absorbed through the gastrointestinal tract, the amount of natamycin that enters the bloodstream after topical application or accidental ingestion is negligible. This minimal systemic absorption is why significant body-wide side effects are rare when used as directed. In fact, studies in rabbits showed no measurable compound in the intraocular fluid or blood serum after topical administration.
Potential side effects from ophthalmic use are typically confined to the eye and include:
- Eye discomfort or irritation
- Redness or swelling of the eye
- Watery eyes
- Feeling like there is a foreign body in the eye
- Changes in vision
- Localized allergic reactions
Natamycin as a Food Preservative (E235)
Beyond its pharmaceutical use, natamycin is a widely used food preservative, designated as E235. It is applied to the surface of various products to prevent the growth of mold and yeast and extend shelf life.
What Happens When You Eat Natamycin?
When consumed as a food additive, natamycin is poorly absorbed from the gastrointestinal tract and is rapidly degraded by stomach acids. Regulatory agencies, including the European Food Safety Authority (EFSA) and the U.S. Food and Drug Administration (FDA), have confirmed its safety profile within specified limits. The acceptable daily intake (ADI) is set far above typical exposure levels from treated foods.
Potential Side Effects from Oral Ingestion
While generally safe, high oral doses (much higher than those found in preserved food) have been shown to cause temporary gastrointestinal upset in humans, such as nausea, vomiting, and diarrhea. For the vast majority of consumers, dietary intake of natamycin is of no toxicological concern.
Natamycin vs. Other Antifungals
| Feature | Natamycin | Amphotericin B | Azole Antifungals (e.g., Voriconazole) |
|---|---|---|---|
| Mechanism of Action | Binds to ergosterol, altering membrane permeability without creating membrane pores. | Binds to ergosterol, creating membrane pores and causing cell leakage. | Inhibit ergosterol synthesis, impairing membrane function. |
| Route of Administration | Primarily topical (ophthalmic, cream, lozenge); limited systemic use. | Both topical and systemic (intravenous) administration. | Primarily systemic (oral, intravenous), but some topical forms exist. |
| Systemic Absorption | Negligible from topical or oral administration. | Poor oral absorption, but highly absorbed via IV. | Well absorbed orally and intravenously. |
| Effectiveness | Highly effective against filamentous fungi like Fusarium in keratitis. | Broad spectrum; used for both superficial and deep infections. | Broad spectrum; used for systemic and some topical infections. |
| Toxicity Profile | Low toxicity, mainly localized side effects with topical use; minimal systemic risk. | Higher risk of systemic toxicity (e.g., kidney damage) with IV use. | Varying toxicity profiles; potential for drug interactions. |
Conclusion
To summarize, what does natamycin do to your body is a question with a clear, specific answer: it acts as a powerful, localized antifungal with minimal systemic impact. Its primary mechanism involves disrupting the cell membranes of fungi by binding to ergosterol, a sterol not found in human cells. Medically, this action is leveraged through topical eye drops for fungal infections like keratitis, where its effects are concentrated at the site of infection with minimal systemic absorption. As a food additive (E235), it provides surface-level protection against mold and yeast, is minimally absorbed when ingested, and poses no significant risk to human health within approved concentrations. Its selective action against fungi and low systemic toxicity make it a valuable tool in both medicine and food preservation.
Helpful Resources
- Drug Summary from PDR.net: For more detailed information on natamycin's medical use, side effects, and mechanism of action, refer to the drug summary provided by PDR.net, a reputable resource for health professionals.
