Effects of Different Drugs on the Viability of Cysts and Trophozoites of Acanthamoeba spp.

• Grant number: 25/15712-3
• Support Opportunities: Scholarships in Brazil - Scientific Initiation
• Start date: October 01, 2025
• End date: September 30, 2026
• Field of knowledge: Biological Sciences - Parasitology - Protozoology of Parasites
• Principal Investigator: Denise de Freitas
• Grantee: Eduarda Ferreira Rocha Polito
• Host Institution: Escola Paulista de Medicina (EPM). Universidade Federal de São Paulo (UNIFESP). Campus São Paulo. São Paulo , SP, Brazil

Abstract

Acanthamoeba keratitis (AK) is a rare but highly morbid infection that affects the cornea. Its etiologic agent is the protozoan Acanthamoeba spp., comprising 25 species and 23 genotypes, of which 12 species and 11 genotypes have been associated with AK. These amoebae are widely distributed in nature, suggesting frequent human exposure - between 50% and 100% of the population have serum antibodies against antigens of this genus. These amphizoic protozoa exist in two evolutionary forms: trophozoites, which are metabolically active and infectious; and cysts, which are structurally resistant and confer greater tolerance to adverse conditions and antimicrobial treatments. Among the infections caused by Acanthamoeba, AK stands out, often linked to improper contact lens use. With variable clinical progression and difficult early diagnosis, it can lead to significant vision loss if not properly treated. Current therapy is based on a combination of biguanides (such as polyhexamethylene biguanide) and diamidines (such as propamidine isethionate - Brolene®); however, treatment response may be limited. In recent years, other drugs have been considered as promising alternatives. This study aims to evaluate the effects of polyaminopropyl biguanide (PAPB), benzalkonium chloride (BAK), chlorhexidine, alexidine, polyquaternium (PQ), and auranofin on the viability of trophozoite and cystic forms of Acanthamoeba spp. A total of 20 clinical isolates from patients with AK will be used, along with two reference strains: A. polyphaga (ATCC 30461), of clinical origin, and A. castellanii (ATCC 30010), of environmental origin. Drug concentrations tested will be 10 uL/mL (0.01%), 20 uL/mL (0.02%), 60 uL/mL (0.06%), 80 uL/mL (0.08%), and 100 uL/mL (0.1%), with analyses performed at 4 h, 12h and 24 h. The minimum inhibitory concentration (MIC) will be determined by microdilution assays in 96-well plates. Cell viability will be assessed using lactophenol cotton blue, acridine orange, calcofluor white, and silver staining.