Genotyping of Acanthamoeba spp. and characterization of the prevalent T4 type along with T10 and unassigned genotypes from amoebic keratitis patients in India

In Vitro Efficacy of Miltefosine Against Clinical Isolates of Acanthamoeba spp. from Patients with Keratitis

PURPOSE

The US Food and Drug Administration (USFDA) granted the miltefosine orphan drug designation in 2016 for treating Acanthamoeba keratitis. This study evaluates miltefosine's in vitro efficacy against clinical isolates of Acanthamoeba from patients with keratitis and its safety profile in human corneal epithelial cell line to rationalize its localized ocular application.

METHODS

Acanthamoeba spp. isolated from corneal scrapings of keratitis patients (n = 17) were cultured axenically, genotyped, and tested for miltefosine's minimal cysticidal and trophozoicidal concentrations (MCC and MTC) by microbroth dilution method. Safer concentrations of miltefosine were determined using human corneal epithelial (HCE) cells at four incubation points. Trophozoites and cysts of one of the isolates, A. castellanii, were challenged on confluent monolayers of HCE in the presence and absence of miltefosine for 24 h. Cytopathic effects were evaluated using microscopic analysis.

RESULTS

The majority of Acanthamoeba isolates tested were T4 genotypes (94.11%). MTC90 and MCC90 of miltefosine were 0.125 and 4 mg/mL, respectively. Miltefosine was found safe on HCE at 0.0625 and 0.125 mg/mL for 4 and 0.25 h, respectively. Microscopical findings showed that A. castellanii trophozoites destroyed the cellular structures of HCE within 24 h without miltefosine. Drug pre-treatment prevented the initiation of infection at both the tested concentrations (0.0625 and 0.125 mg/mL) upto 24 h.

CONCLUSION

Miltefosine was effective against Acanthamoeba trophozoites and cysts in vitro with >30-fold higher cidal concentration for cysts compared to trophozoites. An effective trophozoicidal concentration of miltefosine (0.125 mg/mL), found to be safe for HCEs, suggests its potential utility as an adjunct treatment for Acanthamoeba keratitis.

Molecular evidence for a new lineage within the Acanthamoeba T4 genotype

Acanthamoeba is a widespread free-living amoeba capable of causing serious infections in humans and other animals, such as amoebic keratitis, disseminated infections, and fatal encephalitis. Strain identification is usually based on 18S rDNA sequencing, which allows the distinction of over twenty genotypes. Most sequences from environmental and clinical samples belong to the T4 genotype, which can be divided into seven subtypes, T4A to T4G, and by a nearly similar grouping of mitochondrial sequences into T4a to T4j subtypes. The co-clustering of nuclear and mitochondrial groups can be very useful for a better identification of lineages within the very rich T4 genotype. In this study, we provided molecular phylogenetic evidence for the delineation of a new nuclear subtype, hereafter labelled T4H, and its co-clustering with the mitochondrial T4j subtype. At least three cases of amoebic keratitis are due to strains belonging to this new group, present mainly in fresh water and detected in various countries (France, Iran, India and China).

Molecular detection and genotype identification of Acanthamoeba species from bronchoalveolar lavage of patients with pulmonary symptoms suspected of cancer

Acanthamoeba spp. are the most common free-living amoeba worldwide, inducing life-threatening diseases such as Granulomatous Amoebic Encephalitis, pulmonary infection, and amoebic keratitis. This study aimed to identify the FLA and Acanthamoeba genotypes in patients with pulmonary symptoms suspected of cancer in Kashan's hospitals, Kashan, Iran. This cross-sectional study was conducted on 97 bronchoalveolar lavage samples of patients with respiratory symptoms suspected of lung cancer, who were admitted to the Shahid Beheshti Hospital of Kashan from 2019 to 2020. The samples were cultured onto 1.5% non-nutrient agar enriched with killed Escherichia coli and examined for the presence of FLA. Following amoeba isolation and DNA extraction, Acanthamoeba spp. were determined by Polymerase Chain Reaction using JDP1 and JDP2 primers, which amplified a 490 bp fragment from the 18 S rDNA gene. Eighteen Acanthamoeba isolates were sequenced, and the genotypes were identified. The prevalence of FLA and Acanthamoeba and the relationship between symptoms and demographic variables were analyzed with SPSS Software version 16. The prevalence rates of FLA and Acanthamoeba in the BAL samples was 86.6% and 73.2%, respectively. All Acanthamoeba isolates belonged to the T4 genotype. The most symptoms among Acanthamoeba-positive patients were dyspnea and cough; however, their difference was not statistically significant. The findings indicated the high prevalence of FLA and Acanthamoeba in BAL in the population suspected of cancer in Kashan. Since the T4 genotype is a pathogenic genotype of Acanthamoeba, training health and improving sanitation levels would help to prevent infection.

Isolation and morphological and molecular characterization of waterborne free-living amoebae: Evidence of potentially pathogenic Acanthamoeba and Vahlkampfiidae in Assiut, Upper Egypt

Free-living amoebae (FLA) are gaining attention due to the increasing number of related grave central nervous system (CNS) and sight-threatening eye infections and their role as Trojan horses for many bacteria and viruses. This study was conducted in Assiut City, Egypt to detect the presence of FLA in different water sources using morphological and molecular approaches and determine their potential pathogenicity. A total of 188 water samples (100 tap, 80 tank, and 8 swimming pool samples) were collected, cultivated on non-nutrient agar seeded with Escherichia coli, and inspected for FLA. Thermo- and osmo-tolerance assays were performed to determine their pathogenicity. Polymerase chain reaction and sequence analysis were performed to confirm the identification and analyze the genotype. Overall, 52 samples (27.7%) were positive for FLA. Of these, 20.7% were identified as Acanthamoeba, 1.6% as Vahlkampfiidae, and 5.3% as mixed Acanthamoeba and Vahlkampfiidae. Seven species of Acanthamoeba were recognized, of which A. triangularis, A. polyphaga, A. lenticulata, and A. culbertsoni are thermo- and osmo-tolerant, and A. astronyxis, A. comandoni, and A. echinulata are non-thermo- and non-osmo-tolerant. The phylogeny analysis revealed T4 and T7 genotypes. Among Vahlkampfiids, 61.5% were identified as thermo- and osmo-tolerant Vahlkampfia, and 30.8% were identified as non-pathogenic Naegleria. One isolate (7.7%) was identified as potentially pathogenic Allovahlkampfia, as confirmed by sequencing. This is the first report documenting the occurrence and phylogeny of waterborne FLA (Acanthamoeba/Vahlkampfiidae) in Assiut, Egypt. The presence of potentially pathogenic FLA highlights the possible health hazards and the need for preventive measures.

Environmental water surveillance for free-living amoeba in North India

PURPOSE

Free-living amoebae (FLA) exist in various environmental sources and are the causative agents of many serious human diseases. We surveyed various natural and artificial water bodies in areas of north India to detect the presence of FLA species.

MATERIALS AND METHODS

Surface water samples were collected from 29 water bodies and subjected to microscopy, non-nutrient agar (NNA) culture, and various polymerase chain reaction (PCR) assays for the detection of FLA.

RESULTS

FLA were found in 62.1% (18/29) of the natural and artificial water bodies by NNA culture. Based on PCR based detection, Acanthamoeba spp. was identified in 41.4% (12/29), Vannella spp./Vahlkampfia ovis in 17.2% (5/29) and Naegleria spp. in 20.7% (6/29) of the samples from different locations. PCR-sequencing of Naegleria positive samples identified them as Naegleria australiensis and Naegleria species.

CONCLUSIONS

The present study reports widespread occurrence of medically important FLA species in various natural and artificial water bodies, and highlights the need for regular molecular surveillance of FLA in the environment for better control and prevention of the diseases caused by FLA.

Genotype distribution of Acanthamoeba in keratitis: a systematic review

Acanthamoeba spp. are among the most worldwide prevalent protozoa. It is the causative agent of a disease known as Acanthamoeba keratitis, a painful and severe sight-threatening corneal infection that can lead to blindness. In recent years, the prevalence of Acanthamoeba keratitis has rapidly increased, growing its importance to human health. This systematic review aims to assess the distribution of Acanthamoeba sp. genotypes causing keratitis around the world, considering the sample collected type and the used identification method. Most of the cases were found in Asia and Europe. Not surprisingly, the T4 genotype was the most prevalent worldwide, followed by T3, T15, T11, and T5. Furthermore, the T4 genotype contains a higher number of species. Given the differences in pathology, susceptibility to treatment, and clinical outcome between distinct genotypes, it is essential to genotype isolates from Acanthamoeba keratitis cases to help to establish a better correlation between in vitro and in vivo activities, resulting in better drug therapies and successful treatment in cases of this important ocular infection.

Microbiological diagnosis of Acanthamoebic keratitis: experience from tertiary care center of North India

Acanthamoeba keratitis (AK) is a painful vision-threatening infection caused by pathogenic free-living Acanthamoeba. Due to the non-specific clinical presentation, this condition tends to be misdiagnosed by clinicians. A timely diagnosis is crucial for favorable visual outcome. Three hundred patients with suspected microbial keratitis presenting to the Advanced Eye Center at our tertiary care center in North India during the period from 2014 to 2018 were included. Patient's corneal scrapings, contact lens, lens solution, lens case, and tears were processed for microscopic examination by Giemsa and Calcofluor staining, non-nutrient agar (NNA) culture and molecular diagnosis by conventional PCR (cPCR) and Real-time PCR (qPCR). 18S rDNA gene sequencing was done to assess phylogenetic relationship. AK was found in 3.6% (11/300) of non-bacterial non-fungal keratitis patients. Among microbiological techniques, microscopy for Acanthamoeba was positive in 7 cases, NNA culture was positive in 9 cases and 11 cases were detected both by cPCR and qPCR. The sensitivity of microscopy, culture, cPCR and qPCR was 63.64%, 81.82 %, 100%, and 100% respectively whereas specificity was 100% for all the tests. 18S rDNA sequencing revealed that A. castellanii was the predominant species and isolates were genetically distinct. AK should be considered in the differential diagnosis of infectious keratitis. Molecular tests are useful for rapid, sensitive and specific diagnosis and must be included in workup of keratitis.

Cluster of Post-Operative Endophthalmitis Caused by Acanthamoeba T10 Genotype - A First Report

PURPOSE

To report a cluster of postoperative Acanthamoeba endophthalmitis after routine cataract surgeries.

METHODS

A brief summary of sentinel events leading to the referral of 4 patients of postoperative endophthalmitis to our hospital is followed by clinical descriptions and the various diagnostic approaches and interventions used. Genotyping and phylogenetic analysis are also discussed.

RESULTS

Four cases of postoperative cluster endophthalmitis, presumed to be bacterial and treated as such, were referred to our hospital. The presence of an atypical ring infiltrate in the first case facilitated the diagnosis of Acanthamoeba endophthalmitis. All patients had vitritis, corneal involvement, and scleral inflammation. Multiple diagnostic methods, such as corneal scrapings, confocal microscopy, aqueous and vitreous taps, scleral abscess drainage, histopathological studies, polymerase chain reaction, and genotyping and phylogenetic analyses of isolated Acanthamoeba, were used to confirm the diagnosis of endophthalmitis and to establish the extent of ocular involvement. Various medical and therapeutic interventions used to control the infections were also documented. The isolated Acanthamoeba were confirmed as belonging to the T10 genotype, an environmentally and clinically rare variety.

CONCLUSIONS

This is the first report of a cluster of postoperative T10 genotype Acanthamoeba endophthalmitis, occurring after routine cataract surgery in immunocompetent individuals. Contrary to current perceptions, a rapidly evolving infection can occur with Acanthamoeba.

Immunopathogenicity of Acanthamoeba spp. in the Brain and Lungs

Free-living amoebas, including Acanthamoeba spp., are widely distributed in soil, water, and air. They are capable of causing granulomatous amebic encephalitis, Acanthamoeba pneumonia, Acanthamoeba keratitis, and disseminated acanthamoebiasis. Despite low occurrence worldwide, the mortality rate of Acanthamoeba spp. infections is very high, especially in immunosuppressed hosts. Acanthamoeba infections are a medical problem, owing to limited improvement in diagnostics and treatment, which is associated with incomplete knowledge of pathophysiology, pathogenesis, and the host immune response against Acanthamoeba spp. infection. The aim of this review is to present the biochemical and molecular mechanisms of Acanthamoeba spp.-host interactions, including the expression of Toll-like receptors, mechanisms of an immune response, the activity of metalloproteinases, the secretion of antioxidant enzymes, and the expression and activity of cyclooxygenases. We show the relationship between Acanthamoeba spp. and the host at the cellular level and host defense reactions that lead to changes in the selected host's organs.

Detection and Identification of Acanthamoeba and Other Nonviral Causes of Infectious Keratitis in Corneal Scrapings by Real-Time PCR and Next-Generation Sequencing-Based 16S-18S Gene Analysis

Acanthamoeba is a free-living amoeba of extensive genetic diversity. It may cause infectious keratitis (IK), which can also be caused by bacteria, fungi, and viruses.

Acanthamoeba is a free-living amoeba of extensive genetic diversity. It may cause infectious keratitis (IK), which can also be caused by bacteria, fungi, and viruses. High diagnostic sensitivity is essential to establish an early diagnosis of Acanthamoeba-associated keratitis. Here, we investigated the applicability of next-generation sequencing (NGS)-based ribosomal gene detection and differentiation (16S-18S) compared with specific real-time PCR for the detection of Acanthamoeba. Two hundred DNAs extracted from corneal scrapings and screened by Acanthamoeba-specific real-time PCR were analyzed using an in-house 16S-18S NGS assay. Of these, 24 were positive by specific real-time PCR, of which 21 were positive by the NGS assay. Compared with real-time PCR; the specificity and sensitivity of the NGS assay were 100% and 88%, respectively. Genotypes identified by the NGS assay included T4 (n = 19) and T6 (n = 2). Fungal and bacterial species of potential clinical relevance were identified in 31 of the samples negative for Acanthamoeba, exemplified by Pseudomonas aeruginosa (n = 11), Moraxella spp. (n = 6), Staphylococcus aureus (n = 2), Fusarium spp. (n = 4), and Candida albicans (n = 1). In conclusion, the 16S-18S assay was slightly less sensitive than real-time PCR in detecting Acanthamoeba-specific DNA in corneal scrapings. Robust information on genotypes was provided by the NGS assay, and other pathogens of potential clinical relevance were identified in 16% of the samples negative for Acanthamoeba. NGS-based detection of ribosomal genes in corneal scrapings could be an efficient screening method for detecting nonviral causes of IK, including Acanthamoeba.

18S rDNA sequencing aided diagnosis of Acanthamoeba jacobsi keratitis -A case report

Identification of Acanthamoeba cysts and trophozoites in cases of keratitis is traditionally done with microbiological techniques such as smear examination with 10% potassium hydroxide (KOH) and culture. Double walled cyst with hexagonal inner wall is characteristic of Acanthamoeba. We report a unique case of a 9 year old boy who presented with dense anterior corneal stromal infltration, which on smear examination showed atypical double walled spherical cysts, leading to a diagnostic dilemma. An 18S rRNA gene-based PCR done on the growth on culture, subsequently identifed a rarely reported species of Acanthamoeba. The patient was advised combination therapy with polyhexamethylene biguanide (PHMB 0.02%) and chlorhexidine (0.02%) eye drops. Three weeks post treatment, the keratitis resolved with scarring and vascularisation and visual acuity improved to 20/60. At 8 weeks follow up Best corrected visual acuity further improved to 20/30 with contact lens.

First time identification of Acanthamoeba genotypes in the cornea samples of wild birds; Is Acanthamoeba keratitis making the predatory birds a target?

Acanthamoeba is a free-living amoeba which can be isolated from environment and among others well known as an opportunist protozoan parasite causing infections in humans and animals. Eyes are extremely important for the wild birds and losing sight ability due to Acanthamoeba can be dangerous. The studies on Acanthamoeba infection in wild birds is very few in world and Turkey therefore we aimed to screen deceased wild birds found in İzmir and Manisa provinces located in western Turkey using PCR and non-nutrition agar (NNA) plate method. Cornea samples were obtained from 18 deceased wild birds. During the external examination, signs of keratitis were observed in two Eurasian sparrowhawks (Accipiter nisus). All of the corneal samples were analyzed by two PCR methods and NNA plate. According to results, the Acanthamoeba positivity in corneal samples was 16.6% and 5.5% by PCR and plate method, respectively. According to sequencing data, two of isolates belonged to genotype T5 and one was genotype T4. In conclusion, Acanthamoeba infection was detected in wild bird cornea samples with/without keratitis for the first time in the world. The result of this study also show that Acanthamoeba can be a cause of keratitis in wild birds of Turkey and thus these predator birds can be a target of other wild animals due to loss of sight ability. In terms of public health, these results show the importance of wild birds as a source of Acanthamoeba infection in nature.

Molecular detection and genotyping of Acanthamoeba spp. among stray dogs using conjunctival swab sampling

Acanthamoeba is one of the most common free-living amoebas (FLA) that present in environment. In humans, Acanthamoeba can cause an infection of the eye termed Acanthamoeba keratitis, which mostly occurs in contact lens wearers. In the present study, we aimed to screen the presence of Acanthamoeba DNA in stray dogs using previously collected conjunctival swab samples in a hyper-endemic area for canine leishmaniasis. Totally, 184 dogs were included in the study and 27 of them (14.6%) were found positive for Acanthamoeba according to the 18s rRNA gene sequencing. Two different genotypes (T4 and T5) were identified and T5 was firstly reported in Turkey in the present study. Statistical analysis was performed and no correlation was found between Leishmania and Acanthamoeba positivity (P<0.05). To best of our knowledge, this is the first study conducted to screen Acanthamoeba among stray dogs. Further studies are necessary to reveal the infection status and genotypes among dogs and its possible correlation with leishmaniasis.

Isolation and genotyping of Acanthamoeba spp. from Acanthamoeba meningitis/ meningoencephalitis (AME) patients in India

Background

Acanthamoeba spp. are free-living ubiquitous protozoans capable of causing Acanthamoeba meningitis/meningoencephalitis (AME) of the central nervous system in humans. Acanthamoeba spp. are divided into 20 different genotypes (T1–T20) on the basis of variation in nucleotide sequences of the 18S rRNA gene. The objective of this study was to identify the genotypes of Acanthamoeba spp. in patients of Acanthamoeba meningitis/meningoencephalitis (AME) using 18S rRNA gene-based PCR assay. The present study provides information regarding the involvement of the most prevalent and predominant genotype of Acanthamoeba spp. in Acanthamoeba meningitis/meningoencephalitis infections in India.

Methods

Cerebrospinal fluid (CSF) was collected from 149 clinically suspected Acanthamoeba meningitis/meningoencephalitis (AME) patients reporting to the outpatient department/causality services of the Neurosciences Centre, AIIMS, New Delhi, India during the past five years. Samples were inoculated onto 2 % non-nutrient agar plates overlaid with E. coli and incubated at 30 °C for 14 days. Among 149 suspected patients, ten were found culture-positive for Acanthamoeba spp. out of which six isolates were established in axenic culture for molecular analysis. DNA was isolated and a PCR assay was performed for amplification of the Diagnostic fragment 3 (DF3) (~280 bp) region of the 18S rRNA gene from axenic culture of six Acanthamoeba spp. isolates. Rns genotyping was performed on the basis of the variation in nucleotide sequences of DF3 region of the 18S rRNA gene.

Results

In the phylogenetic analysis, all of the six Acanthamoeba spp. isolates were found to belong to genotype T4. The sequence homology search for these six isolates in the NCBI databank showed homology with the available strains of Acanthamoeba spp. The newly generated sequences are available in the GenBank database under accession numbers KT004416–KT004421.

Conclusions

In the present study, genotype T4 was found as the most prevalent and predominant genotype in Acanthamoeba meningitis/ meningoencephalitis infections. Hence further studies are needed to develop optimal therapeutic strategy against Acanthamoeba spp. of genotype T4 to combat against the infections.