Activity of Silver Nitrate for Treatment of Amoebic Keratitis

Silver nitrate is an inorganic salt that is active against a wide range of microorganisms, mainly bacteria and fungi. The emergence of antibiotics and new medications led to the abandonment of silver nitrate by modern medicine, however microbial resistance to existing medications led to the re-emergence of the use of silver nitrate by the scientific community. Amoebic keratitis is a serious condition associated to the use of contact lenses. Very often this disease results in blindness and its prevalence is increasing along with the number of lens wearers. It is caused by a free-living amoeba belonging to the genus Acanthamoeba. Currently, amoebic keratitis has no specific treatment and what it is available is quite prolonged and requires extreme discipline from the patient. In this study the trophozoites were cultured in PYG medium and subsequently incubated with different concentrations of silver nitrate. Trophozoite viability was assessed after 120 hours using the Trypan blue exclusion test. Morphological changes were evaluated by optical and transmission electron microscopy. .Concentrations above 0.1 mg/mL of silver nitrate have an amoebicidal effect in vitro in 5 days of incubation; a concentration of 1 mg/mL is capable of causing the death of more than 90% of the amoebas tested, in just 15 minutes. The results obtained suggest that silver nitrate-based eye drops can help or form part of a treatment against amoebic keratitis. In conclusion, silver nitrate showed an important amoebicidal effect, in the concentration range of 0.1 to 1 mg/mL.

Keywords:
Amoebic keratitis; Acanthamoeba; contact lenses.

Electron microscopy has shown that silver nitrate promotes membrane rupture

Concentrations above 0.1 mg/mL of silver nitrate have an amoebicidal effect;

1 mg/mL is capable of causing the death of more than 90% of the amoebas tested.