Identification of Acanthamoeba sp. with Different Microscopes and Analysis of the Anatomical Changes from Trophozoite to Cyst form with an Electron Microscope

Background: Acanthamoeba is a free living ubiquitous protozoa, capable of causing Acanthamoeba keratitis (AK) of eyes and Acanthamoeba meningitis/ meningoencephalitis (AME) of central nervous system in human. Identification of amoeba is possible by a light microscope but, due to its poor resolution power, it is insufficient to distinguish the intimate sub cellular structures. As the resolution power of Differential Interference Contrast microscope (DIC) is more compared to light microscope, it can perfectly distinguish the trophozoite and cyst forms of amoeba on the basis of morphology, but the detailed understanding and characterization of the inner cell structure and sub cellular organelles is only possible with an electron microscope. Methods: Corneal scraping was collected from a clinically suspected AK patient reporting to the outpatient department (OPD) of Dr RP. Centre for Ophthalmic Sciences, All India Institute of Medical Sciences, India with prior consent and thorough clinical examination under a slit lamp. Specimen was plated carefully onto a 2% non-nutrient agar plate previously seeded with live E. coli. Growth of amoeba over the agar surface was confirmed with a light microscope. DIC microscope and electron microscope were implemented to study the morphology and anatomy of Acanthamoeba. Results: Prominent spine like structures i.e. acanthapodia were clearly visible on the outer surface of Acanthamoeba trophozoites and prominent double layer cell wall (exocyst and endocyst) was seen in the mature cyst form with DIC microscope. Several oval mitochondrias, food vacuoles and water expulsion vacuoles were seen within the cytoplasm of trophozoite of Acanthamoeba sp. by electron microscopy. Number of Golgi bodies were more within the cyst and found close to the inner cell wall. Conclusions: Although identification of Acanthamoeba sp. can be possible with light and DIC microscopes but analysis of the anatomical changes from trophozoite to cyst forms can be studied with an electron microscope.