الفهرس 
Historical ReviewOnly 14 pages are availabe for public view
 |  | from | 206 |  |  |
| | | from | 206 | | |
Abstract
Background: Genus Acanthamoeba is commonly found in soil and aquatic environments worldwide. Acanthamoebae are the most common opportunistic amphizoic protozoa that cause life-threatening granulomatous amoebic encephalitis in immunocompromised individuals and sight-threatening amoebic keratitis (AK) in contact lens wearers. The incidence of AK infection has increased exponentially during the last 30 years. Additionally, they may help transmit microbial endosymbionts to the susceptible hosts which contribute to the pathogenicity. A reliable identification method of genotypes based on the nuclear 18S small subunit ribosomal RNA gene (Rns) sequence is now used worldwide. Phylogenetic analysis has led to the identification of 19 different genotypes (T1-T19) however; attempts to correlate pathogenicity with certain genotypes are under investigation.
Aim: The present work aimed to determine the presence of Acanthamoeba spp. in different environmental sources: water, soil and dust from some districts in Cairo Governorate and characterize the pathogenic potential of the isolated Acanthamoeba spp. using physiological and biochemical assays as well as determination of the genotypes of the potentially pathogenic environmental isolates in an attempt to correlate pathogenicity with genotypes.
Materials and Methods: The study included the collection of 22 corneal scrapings from clinically diagnosed AK patients and 75 environmental samples including 35 water, 30 soil and 10 dust samples, they were cultivated on non-nutrient agar plates preseeded with E. coli (NNA- E. coli). Positive samples for Acanthamoeba were subjected to osmotolerance and temperature tolerance assays and Zymography analysis; to determine the pathogenic potential of Acanthamoeba environmental isolates in comparison to pathogenic isolates from AK patients. Potentially pathogenic environmental Acanthamoeba isolates were subjected to PCR followed by partial sequencing of the Rns including DF3 and genotype identification.
Results: The total detection rate for Acanthamoeba in environmental samples was 33.3% (25 out of 75); collected from water 31.4% (11 out of 35), dust 20% (2 out of 10) and soil 40% (12 out of 30). It was found that 70.6 % (12 out of 17) and 76.5% (13 out of 17) of the Acanthamoeba isolates obtained from the environment demonstrated pathogenic potential using osmotolerance and temperature tolerance assays, respectively. Proteolytic activity of some water and soil isolates resembled the proteolytic activity of all AK isolates. Three and two Acanthamoeba isolates from water and soil sources respectively were classified as potential pathogens as they exhibited full range of pathogenic traits. Other 12 isolates (5 from water, 5 from soil and 2 from dust) were designated as weak potential pathogens as they didn’t exhibit full range of pathogenic traits. Only 10 of the environmental isolates were positive in PCR and were classified by genotype analysis into T4 genotype (70%), T3 (10%) and T5 (20%). Potential pathogens belonged to genotypes T4 (from water) and T5 (from soil) while weak potential pathogens belonged to genotypes T3 (from water) and T4 (from water and soil). Additionally, T7 genotype was isolated from keratitis patients.
Conclusions: There is a considerable variation in the response of Acanthamoeba members of the same genotype to physiological and biochemical assays making generalization difficult. Although there are only limited variants of Acanthamoeba genotypes in studied Cairo districts, presence of potentially pathogenic Acanthamoeba strains in habitats related directly to human populations represents a risk for human health. Isolation of Acanthamoeba genotype T7 from AK cases, which is commonly considered as nonpathogenic, might draw the attention to other Acanthamoeba genotypes considered as non pathogenic and reevaluate their role in production of human infections.