# Sodium Metabisulfite Inhibits Acanthamoeba Trophozoite Growth through Thiamine Depletion

## TL;DR

Sodium metabisulfite, found in eye drops, inhibits Acanthamoeba growth by depleting thiamine, a nutrient the organism cannot make itself.

## Contribution

The study identifies sodium metabisulfite as a novel inhibitor of Acanthamoeba trophozoites through thiamine depletion.

## Key findings

- Sodium metabisulfite inhibits Acanthamoeba trophozoites at low concentrations (IC50 0.03 mg/mL).
- Acanthamoeba is a thiamine auxotroph, requiring external thiamine for growth.
- Thiamine supplementation reverses the inhibitory effects of sodium metabisulfite.

## Abstract

Acanthamoeba keratitis (AK) is a severe infection of the cornea. Prevention and treatment are difficult due to the inefficacy of currently available compounds. The impact of many commonly used compounds for routine examinations of Acanthamoeba is unexplored but might offer insight useful in combatting AK. In this study, we demonstrate that sodium metabisulfite, a common preservation constituent of eye care solutions, was found to be active against Acanthamoeba trophozoites at concentrations lower than that commonly found in eye drops (IC50 0.03 mg/mL). We demonstrate that sodium metabisulfite depletes thiamine from growth medium and that Acanthamoeba is a thiamine auxotroph, requiring thiamine salvage for growth. The inhibitory effects of sodium metabisulfite can be overcome by thiamine supplementation. These results are consistent with the lack of key enzymes for thiamine biosynthesis in the genome of Acanthamoeba, an area which might prove exploitable using new or existing compounds. Indeed, this study highlights sodium metabisulfite as a useful inhibitor of Acanthamoeba castellanii trophozoites in vitro and that it acts, at least in part, by limiting available thiamine.