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      An update on Acanthamoeba keratitis: diagnosis, pathogenesis and treatment Translated title: Mise au point sur la kératite à Acanthamoeba : diagnostic, pathogenèse et traitement

      1 , * , 2 , 3


      EDP Sciences

      Acanthamoeba, keratitis, diagnosis, therapy, pathogenesis

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          Free-living amoebae of the genus Acanthamoeba are causal agents of a severe sight-threatening infection of the cornea known as Acanthamoeba keratitis. Moreover, the number of reported cases worldwide is increasing year after year, mostly in contact lens wearers, although cases have also been reported in non-contact lens wearers. Interestingly, Acanthamoeba keratitis has remained significant, despite our advances in antimicrobial chemotherapy and supportive care. In part, this is due to an incomplete understanding of the pathogenesis and pathophysiology of the disease, diagnostic delays and problems associated with chemotherapeutic interventions. In view of the devastating nature of this disease, here we present our current understanding of Acanthamoeba keratitis and molecular mechanisms associated with the disease, as well as virulence traits of Acanthamoeba that may be potential targets for improved diagnosis, therapeutic interventions and/or for the development of preventative measures. Novel molecular approaches such as proteomics, RNAi and a consensus in the diagnostic approaches for a suspected case of Acanthamoeba keratitis are proposed and reviewed based on data which have been compiled after years of working on this amoebic organism using many different techniques and listening to many experts in this field at conferences, workshops and international meetings. Altogether, this review may serve as the milestone for developing an effective solution for the prevention, control and treatment of Acanthamoeba infections.

          Translated abstract

          Les amibes à vie libre du genre Acanthamoeba sont les agents causant une infection sévère de la cornée, dangereuse pour la vue, appelée kératite à Acanthamoeba. De plus, le nombre de cas signalés à travers le monde est en augmentation année après année, principalement chez les porteurs de lentilles de contact, bien que des cas de kératite à Acanthamoeba aient également été signalés chez les non-porteurs de lentilles. Fait intéressant, la kératite à Acanthamoeba est restée significative, en dépit de nos progrès dans la chimiothérapie antimicrobienne et les soins de soutien. En partie, cela est dû à une compréhension incomplète de la pathogenèse et la physiopathologie de la maladie, aux retards du diagnostic et aux problèmes associés aux interventions chimiothérapeutiques. Compte tenu de la nature dévastatrice de cette maladie, nous présentons ici notre compréhension actuelle de la kératite à Acanthamoeba et des mécanismes moléculaires associés à la maladie, ainsi que les traits de virulence de Acanthamoeba qui peuvent être des cibles potentielles pour l’amélioration du diagnostic, les interventions thérapeutiques et/ou pour l’élaboration de mesures préventives. Des approches moléculaires comme la protéomique, l’ARNi et des approches consensuelles de diagnostic pour un cas suspecté de kératite à Acanthamoeba sont proposées et examinées sur la base des données qui ont été compilées après des années de travail sur cet organisme amibien, utilisant de nombreuses techniques différentes et l’écoute de nombreux experts sur ce domaine à des conférences, ateliers et réunions internationales. Au total, cette étude peut servir de jalon pour développer une solution efficace pour la prévention, le contrôle et le traitement des infections à Acanthamoeba.

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          Most cited references 117

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          Structures and mechanisms of glycosyl hydrolases.

          The wealth of information provided by the recent structure determinations of many different glycosyl hydrolases shows that the substrate specificity and the mode of action of these enzymes are governed by exquisite details of their three-dimensional structures rather than by their global fold.
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            Use of subgenic 18S ribosomal DNA PCR and sequencing for genus and genotype identification of acanthamoebae from humans with keratitis and from sewage sludge.

            This study identified subgenic PCR amplimers from 18S rDNA that were (i) highly specific for the genus Acanthamoeba, (ii) obtainable from all known genotypes, and (iii) useful for identification of individual genotypes. A 423- to 551-bp Acanthamoeba-specific amplimer ASA.S1 obtained with primers JDP1 and JDP2 was the most reliable for purposes i and ii. A variable region within this amplimer also identified genotype clusters, but purpose iii was best achieved with sequencing of the genotype-specific amplimer GTSA.B1. Because this amplimer could be obtained from any eukaryote, axenic Acanthamoeba cultures were required for its study. GTSA.B1, produced with primers CRN5 and 1137, extended between reference bp 1 and 1475. Genotypic identification relied on three segments: bp 178 to 355, 705 to 926, and 1175 to 1379. ASA.S1 was obtained from single amoeba, from cultures of all known 18S rDNA genotypes, and from corneal scrapings of Scottish patients with suspected Acanthamoeba keratitis (AK). The AK PCR findings were consistent with culture results for 11 of 15 culture-positive specimens and detected Acanthamoeba in one of nine culture-negative specimens. ASA.S1 sequences were examined for 6 of the 11 culture-positive isolates and were most closely associated with genotypic cluster T3-T4-T11. A similar distance analysis using GTSA.B1 sequences identified nine South African AK-associated isolates as genotype T4 and three isolates from sewage sludge as genotype T5. Our results demonstrate the usefulness of 18S ribosomal DNA PCR amplimers ASA.S1 and GTSA.B1 for Acanthamoeba-specific detection and reliable genotyping, respectively, and provide further evidence that T4 is the predominant genotype in AK.
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              Conserved catalytic machinery and the prediction of a common fold for several families of glycosyl hydrolases.

              The regions surrounding the catalytic amino acids previously identified in a few "retaining" O-glycosyl hydrolases (EC 3.2.1) have been analyzed by hydrophobic cluster analysis and have been used to define sequence motifs. These motifs have been found in more than 150 glycosyl hydrolase sequences representing at least eight established protein families that act on a large variety of substrates. This allows the localization and the precise role of the catalytic residues (nucleophile and acid catalyst) to be predicted for each of these enzymes, including several lysosomal glycosidases. An identical arrangement of the catalytic nucleophile was also found for S-glycosyl hydrolases (myrosinases; EC for which the acid catalyst is lacking. A (beta/alpha)8 barrel structure has been reported for two of the eight families of proteins that have been grouped. It is suggested that the six other families also share this fold at their catalytic domain. These enzymes illustrate how evolutionary events led to a wide diversification of substrate specificity with a similar disposition of identical catalytic residues onto the same ancestral (beta/alpha)8 barrel structure.

                Author and article information

                EDP Sciences
                18 February 2015
                : 22
                : ( publisher-idID: parasite/2015/01 )
                [1 ] University Institute of Tropical Diseases and Public Health of the Canary Islands, University of La Laguna, Avda. Astrofísico Fco. Sánchez, S/N 38203 La Laguna, Tenerife, Canary Islands Spain
                [2 ] Department of Biological and Biomedical Sciences, Aga Khan University Karachi Pakistan
                [3 ] Institute of Specific Prophylaxis and Tropical Medicine, Medical University of Vienna Vienna Austria
                Author notes

                All authors contributed equally to this manuscript.

                [* ]Corresponding author: jmlorenz@ 123456ull.edu.es
                parasite140120 10.1051/parasite/2015010
                © J. Lorenzo-Morales et al., published by EDP Sciences, 2015

                This is an Open Access article distributed under the terms of the Creative Commons Attribution License ( http://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

                Page count
                Figures: 8, Tables: 3, Equations: 0, References: 118, Pages: 20
                Review Article

                pathogenesis, acanthamoeba, keratitis, diagnosis, therapy


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