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Marina Roizenblatt, Linda C Carrijo-Carvalho, Annette S Foronda, Fabio R Carvalho, Denise Freitas; Effect of biguanide on excystment, proliferation and death of Acanthamoeba strains. Invest. Ophthalmol. Vis. Sci. 2014;55(13):5788.
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Acanthamoeba keratitis is a sight-threating infection which can progress into the eye, causing corneal ulcer, loss of visual acuity and eventually blindness. There is a lack of a standard therapy. The treatment is based on topical instillation of biguanides and/ or diamidines at higher concentration and these compounds seems to be toxic to corneal cells. The present study was designed to investigate the antimicrobial activity of a biguanide, at a lower concentration, against Acanthamoeba cysts isolated from a severe AK case, comparing the susceptibility pattern with an avirulent strain of the protozoa.
The study was approved by the local ethics committee. The effect of polyhexamethylene biguanide (PHMB) at 0.02% was evaluated in an avirulent Acanthamoeba strain (ATCC 30011) and a clinical isolate. Induction of death, excystment and proliferation of protozoa at 12 and 72 h were evaluated by quantitative analysis. The experimental procedures were carried out in triplicate. Data were subjected to one-way ANOVA and results were considered statistically significant when p < 0.05.
Our findings demonstrated a reduction of 44.5 and 61.6% in the total number of trophozoites from ATCC 30011 and clinical isolate, respectively, at the time of 12 h. After 72 h, the reduction was 94.9 and 85.4% for ATCC 30011 and the clinical isolate, respectively. Avirulent strain and clinical isolate were equally susceptible to PHMB at 12 h, while the clinical isolate showed increased resistance to PHMB action after 72 h, with a high viability rate.
Differential patterns of resistance against PHMB were demonstrated between Acanthamoeba strains. Data suggest the hypothesis of PHMB acts in the viability and proliferation of trophozoites and not in the inhibition of excystment of the protozoa. Our findings demonstrates the importance of an earlier and specific therapeutic profile and the key role of patient in regular usage of PHMB in order to avoid the eventual occurrence of acquired resistance strain during the treatment for AK. Finally, the results open perspectives about the dosage and frequency of PHMB 0.02% to be used in the treatment of AK.
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