ABSTRACT
Background Acanthamoeba keratitis is a sort of serious infectious eye disease with high causing-blindness rate.Acanthamoeba keratitis often is misdiagnosed as fungal keratitis or viral keratitis in the early stage.Because conventional clinical diagnosis methods show a low specificity and take a long time,timely treatment often is delayed.Conventional PCR does not apply well because the lesion sample is not enough to extract DNA.However,direct PCR can amplify 18S rRNA conserved sequence of acanthamoeba keratitis without the extraction of DNA.Objective This study was to discuss the feasibility for rapid diagnosis of acanthamoeba keratitis using direct PCR to amplify the gene 18S rRNA fragment.Methods Ten acanthamoeba strains were isolated from 10 eyes with acanthamoeba keratitis in Qingdao Eye Hospital.The sensitivity of the direct PCR assay was tested using different numbers of amoebas.The specificity of the assay was tested using DNA extracted from acanthamoeba,candida albicans,pseudomonas aeruginosa,herpes simplex virus-1 (HSV-1) and normal human corneal epithelial cell.Acanthamoeba keratitis models were established using infected method in clean 6-week-old female BALB/c mice.Corneal lesion samples were obtained 1 day,3,5,7,10,15 days after modeled.The effectivity and feasibility of the direct PCR assay for rapid diagnosis of acanthamoeba keratitis were evaluated and compared with culture method,corneal smear examination and real-time PCR.Results Direct PCR primers could only amplify DNA of acanthamoeba rather than other pathogens,and 10 stains of acanthamoeba were detected at least in each sample.During the development of acanthamoeba keratitis in the mice,the diagnosis positive rate of direct PCR was 80.0％,90.0％,80.0％,70.0％,70.0％ and 50.0％ in 1 day,3,5,7,10,15 days after modeled with the total positive rate 73.3％,which was higher than 31.7％ of culture method,56.7％ of corneal smear examination and 61.7％ of realtime PCR,with a significant difference between the direct PCR and culture method (P =0.005),but no significant difference was seen in the total positive rate between the direct PCR and real-time PC R (P =0.172) or corneal smear examination (P =0.056).Conclusions The direct PCR assay is a simple,rapid,highly specific and sensitive method for the rapid diagnosis of acanthamoeba keratitis,especially for the limited lesion sample.