Natamycin

Natamycin, also known as pimaricin, is a naturally occurring antimicrobial agent produced by the bacterium Streptomyces natalensis. It is a macrolide polyene antifungal drug used to treat fungal keratitis. It is especially effective against Aspergillus and Fusarium corneal infections.

In foods
It is used in the food industry as a preservative to inhibit fungal growth on cheese and other food. It may be applied in a liquid spray or in powdered form on whole, shredded, or soft cheese, or applied on or in the wax covering of some cheeses.

As a food additive, it has E number E235.

Medical
Natamycin is used to treat fungal infections, including Candida, Aspergillus, Cephalosporium, Fusarium and Penicillium. It is applied as a cream, in eyedrops, or (for oral infections) in a lozenge. Natamycin shows negligible absorption into the body when administered in these ways. When taken orally, little or none is absorbed from the gastrointestinal tract, making it inappropriate for systemic infections.

Safety
Natamycin lacks acute toxicity. In animal studies, the lowest LD50 found was 450 mg/kg. In rats, the LD50 is ≥2300 mg/kg, and doses of 500 mg/kg/day over 2 years caused no detectable differences in survival rate, growth, or incidence of tumors. The metabolites of natamycin also lack toxicity. The breakdown products of natamycin under various storage conditions may have a lower LD50 than natamycin, but in all cases the numbers are quite high. In humans, a dose of 500 mg/kg/day repeated over multiple days caused nausea, vomiting, and diarrhea.

There is no evidence that natamycin, at either pharmacological levels or levels encountered as a food additive, can harm normal intestinal flora, but definitive research may not be available.