comparison of a pcr-based method with culture and direct examination for diagnosis of acanthamoeba keratitis

background: the aim was to compare three different methods (direct examination, culture and pcr meth­ods) for the diagnosis of acanthamoeba keratitis (ak) in corneal scrapes. methods: twenty eight corneal scrapes and contact lenses were collected from keratitis patients and re­ferred to the de­partment of medical parasitology and mycology, school of public health, tehran univer­sity of medical sci­ences. corneal scrapes were divided in three parts for direct examination, culture on non-nutrient agar and pcr analysis. pcr analysis was also performed using a 18s rrna gene primer pair (df3 region). df3 (diagnostic frag­ment 3) is a region of the nuclear small subunit ribosomal rna gene which is specific for detecting acan­thamoeba strains. results:   acanthamoeba was the causative agent of keratitis in 50% of the patients. direct smear of all pre­pared corneal scrapes in ak patients was negative and culture was positive in only 14.3% of the isolates. pcr analysis was positive in 71.4% of ak patients. these three methods were negative in corneal scrapes of non-ak patients. the sensitivity and specificity of pcr technique for the detection of acanthamoeba sp. were calculated as 71.4% and 100%, respectively. conclusion: according to high sensitivity and specificity of pcr-based method, this study confirmed that pcr using 18s rrna gene primers (df3 region) is more useful for detecting ak cases compare to culture and direct microscopy methods.