Correlations between morphological, molecular biological, and physiological characteristics in clinical and nonclinical isolates of Acanthamoeba spp

Validation and redescription of Acanthamoeba terricola Pussard, 1964 (Amoebozoa: Acanthamoebidae)

Acanthamoeba castellanii (Douglas, 1930) Page, 1967 is the type species of a widespread genus of free-living amoebae, potentially pathogenic for humans and animals. The Neff strain is one of the most widely used in biological research, serving as a model for both A. castellanii and the whole genus in general. The Neff strain, isolated in California, closely resembles another strain found in France and originally described as a separate species, Acanthamoeba terricola Pussard, 1964, but both were successively synonymized with A. castellanii. Molecular sequence analysis has largely replaced morphological diagnosis for species identification in Acanthamoeba, and rDNA phylogenies show that the Neff strain forms a distinct lineage from that of the type strain of A. castellanii. In this study, we compared the type strain of A. terricola with the Neff strain and A. castellanii, and analysed the available molecular data including new sequences obtained from A. terricola. Here we provide molecular evidence to validate the species A. terricola. The Neff strain is therefore transferred to A. terricola and should no longer be considered as belonging to A. castellanii.

Characterization of novel extracellular proteases produced by Acanthamoeba castellanii after contact with human corneal epithelial cells and their relevance to pathogenesis

BACKGROUND

Proteases produced by Acanthamoeba spp. play an important role in their virulence and may be the key to understanding Acanthamoeba pathogenesis; thus, increasing attention has been directed towards these proteins. The present study aimed to investigate the lytic factors produced by Acanthamoeba castellanii during the first hours of in vitro co-culture with human corneal epithelial cells (HCECs).

METHODS

We used one old and one recent Acanthamoeba isolate, both from patients with severe keratitis, and subsets of these strains with enhanced pathogenic potential induced by sequential passaging over HCEC monolayers. The proteolytic profiles of all strains and substrains were examined using 1D in-gel zymography.

RESULTS

We observed the activity of additional proteases (ranging from 33 to 50 kDa) during the early interaction phase between amoebae and HCECs, which were only expressed for a short time. Based on their susceptibilities to protease inhibitors, these proteases were characterized as serine proteases. Protease activities showed a sharp decline after 4 h of co-incubation. Interestingly, the expression of Acanthamoeba mannose-binding protein did not differ between amoebae in monoculture and those in co-culture. Moreover, we observed the activation of matrix metalloproteinases in HCECs after contact with Acanthamoeba.

CONCLUSIONS

This study revealed the involvement of two novel serine proteases in Acanthamoeba pathogenesis and suggests a pivotal role of serine proteases during Acanthamoeba-host cell interaction, contributing to cell adhesion and lysis.

Global prevalence of potentially pathogenic free-living amoebae in sewage and sewage-related environments-systematic review with meta-analysis

Free-living amoebae (FLA) include amphizoic microorganisms important in public health, widely isolated from air, water, and soil. However, its occurrence in sewage-related environments still needs to be systematically documented. This study summarizes the occurrence of FLA in sewage-related environments through a systematic review with meta-analysis. A total of 1983 scientific article were retrieved from different databases, of which 35 were selected and analyzed using a random effects forest plot model with a 95% confidence interval (IC). The pooled overall prevalence of FLA in sewage across 12 countries was 68.96% (95% IC = 58.5-79.42). Subgroup analysis indicates high prevalence in all environments analyzed, including sewage water from the sewage treatment plant (81.19%), treated sewage water (75.57%), sewage-contaminated water (67.70%), sediment contaminated by sewage (48.91%), and sewage water (47.84%). Prevalence values of Acanthamoeba spp., Hartmanella/Vermamoeba spp., and Naegleria spp. are 47.48%, 28.24%, and 16.69%, respectively. Analyzing the species level, the distribution is as follows: Acanthamoeba palestinensis (88%), A. castellanii (23.74%), A. astronyxis (19.18%), A. polyphaga (13.59%), A. culbertsoni (12.5%), A. stevensoni (8.33%), A. tubiashi (4.35%) and A. hatchetti (1.1%), Naegleria fowleri (28.4%), N. gruberi (25%), N. clarki (8.33%), N. australiensis (4.89%) and N. italica (4.29%), Hartmannella/Vermamoeba exundans (40%) and H.V. vermiform (32.61%). Overall, our findings indicate a high risk associated with sewage-related environments, as the prevalence of FLA, including pathogenic strains, is high, even in treated sewage water. The findings of this study may be valuable both for risk remediation actions against amoebic infections and for future research endeavors.

First Report of Isolation and Characterization of Acanthamoeba spp. from the Milk Used for Calf Feeding

PURPOSE

Acanthamoeba spp. can be found in natural and artificial environments, which reflects their high adaptability to different conditions. Based on the available data, there is scarce information about the isolation of amoeba from milk. This study aimed to investigate the probable presence of Acanthamoeba in milk used for calf feeding.

METHODS

200 milk samples from 50 industrial and traditional farms were collected. The samples were filtered and cultured on the 1.5% Non-nutrient agar medium. The amoebic growth was examined with an inverted microscope daily. DNA was extracted from the positive plates, and a PCR reaction was undertaken using the primers amplifying the Acanthamoeba 18 S rRNA gene. Five samples were purified and sequenced using specific primers. Maximum likelihood reconstructions were performed using the phylogenetic program MEGA software. The osmo and thermotolerance of isolated trophozoites were examined as well.

RESULTS

Out of 200 milk samples, Acanthamoeba was isolated from 27 (13.5%). The phylogenetic tree represents that all the isolates belonged to the genotype T4. Results of thermo and osmotolerance tests showed that isolates could develop at 37 and 43 ◦C. Besides, trophozoites survived at 0.5 M mannitol and 1 M.

CONCLUSION

For the first time, Acanthamoeba spp. were isolated from milk used to feed dairy calves. Due to Acanthamoeba's neglected role in pathogen persistence and survival, hygiene instructions should be reconsidered.

Epidemiology of and Genetic Factors Associated with Acanthamoeba Keratitis

Acanthamoeba keratitis (AK) is a severe, rare protozoal infection of the cornea. Acanthamoeba can survive in diverse habitats and at extreme temperatures. AK is mostly seen in contact lens wearers whose lenses have become contaminated or who have a history of water exposure, and in those without contact lens wear who have experienced recent eye trauma involving contaminated soil or water. Infection usually results in severe eye pain, photophobia, inflammation, and corneal epithelial defects. The pathophysiology of this infection is multifactorial, including the production of cytotoxic proteases by Acanthamoeba that degrades the corneal epithelial basement membrane and induces the death of ocular surface cells, resulting in degradation of the collagen-rich corneal stroma. AK can be prevented by avoiding risk factors, which includes avoiding water contact, such as swimming or showering in contact lenses, and wearing protective goggles when working on the land. AK is mostly treated with an antimicrobial therapy of biguanides alone or in combination with diaminidines, although the commercial availability of these medicines is variable. Other than anti-amoeba therapies, targeting host immune pathways in Acanthamoeba disease may lead to the development of vaccines or antibody therapeutics which could transform the management of AK.

The gene expression and proteomic profiling of Acanthamoeba isolates

INTRODUCTION

The free-living protozoan Acanthamoeba can cause severe keratitis known as Acanthamoeba Keratitis (AK) and granulomatous amoebic encephalitis (GAE). The pathogenesis of Acanthamoeba includes intricate interactions between the organism and the host's immune system. The downstream analysis of a well-annotated genome assembly along with proteomic analysis can unravel several biological processes and aid in the identification of potential genes involved in pathogenicity.

METHODS

Based on the next-generation sequencing data analysis, genes including lysophospholipase, phospholipase, S8/S53 peptidase, carboxylesterase, and mannose-binding protein were selected as probable pathogenic targets that were validated by conventional PCR in a total of 30 Acanthamoeba isolates. This was followed by real-time PCR for the evaluation of relative gene expression in the keratitis and amoebic encephalitis animal model induced using keratitis (CHA5), encephalitis (CHA24) and non-pathogenic environmental isolate (CHA36). In addition, liquid chromatography-mass spectrometry (LC-MS/MS) was performed for keratitis, encephalitis, and non-pathogenic environmental isolate before and after treatment with polyhexamethylene biguanide (PHMB).

RESULTS

The conventional PCR demonstrated the successful amplification of lysophospholipase, phospholipase, S8/S53 peptidase, carboxylesterase, and mannose-binding protein genes in clinical and environmental isolates. The expression analysis revealed phospholipase, lysophospholipase, and mannose-binding genes to be significantly upregulated in the keratitis isolate (CHA 5) during AK in the animal model. In the case of the amoebic encephalitis model, phospholipase, lysophospholipase, S8/S53 peptidase, and carboxylesterase were significantly upregulated in the encephalitis isolate compared to the keratitis isolate. The proteomic data revealed differential protein expression in pathogenic versus non-pathogenic isolates in the pre and post-treatment with PHMB.

CONCLUSION

The gene expression data suggests that lysophospholipase, phospholipase, S8/S53 peptidase, carboxylesterase, and mannose-binding protein (MBP) could play a role in the contact-dependent and independent mechanisms of Acanthamoeba pathogenesis. In addition, the proteomic profiling of the 3 isolates revealed differential protein expression crucial for parasite growth, survival, and virulence. Our results provide baseline data for selecting possible pathogenic targets that could be utilized for designing knockout experiments in the future.

Occurrence, molecular diversity and pathogenicity of Acanthamoeba spp. isolated from aquatic environments of Northeastern Brazil

Acanthamoeba is a free-living amoeba (FLA) that is ubiquitous in nature and can cause serious pathologies in humans. This protozoan has been detected in several environmental sources, such as soil, water, and swimming pools. The aim of this study was to evaluate the occurrence and molecular diversity of Acanthamoeba spp. in aquatic environments of the state of Sergipe, northeastern Brazil, and to determine the pathogenic potential of the isolated samples. A total of 138 samples were collected from 69 aquatic environments and, after cell culture, 74% of the samples were positive for FLA, 47% belonging to the genus Acanthamoeba. Genotypic analysis was performed using the primers JDP1 and JDP2, confirming distinct Acanthamoeba genotypes: 18 (75%) isolates belonging to genotype T4, two (8%) to T3, and one isolate (4%) to genotype T5. Tests carried out to analyze the pathogenic potential showed that 11 isolates could grow at 0.5 M mannitol concentration and seven isolates supported hyperosmolarity. In the thermotolerance test, two isolates grew at 37°C. These results confirm the presence and the pathogenic potential of FLA of the genus Acanthamoeba in aquatic environments of the municipalities of Sergipe.

Comparing cytotoxicity and efficacy of miltefosine and standard antimicrobial agents against Acanthamoeba trophozoites and cyst forms: An in vitro study

Acanthamoeba keratitis (AK) is an eye disease often occurring in contact lens wearers. AK treatment is prolonged and requires multiple drugs, which can lead to adverse effects. Our study aimed to compare the in vitro activities and safety of Miltefosine with that of conventional antimicrobial agents used to treat AK. Acanthamoeba castellanii genotype T4 was obtained from a patient with keratitis and subjected to in vitro susceptibility testing with various antimicrobial agents, including Chlorhexidine (CHX), Pentamidine isethionate (PI)Polyhexamethylene biguanide (PHMB), and Miltefosine to assess their efficacy against Acanthamoeba trophozoites and cyst. The cytotoxicity of the agents was evaluated in Vero cells, and their selectivity indexes (SI) were calculated. Chlorhexidine exhibited the highest amoebicidal activity with the highest selectivity index against the trophozoite and cyst, ranging from 1.17 to 8.35. The selectivity index of PHMB is slightly comparable to Chlorhexidine, exhibiting significant anti-Acanthamoeba activity. On the other hand, Pentamidine isethionate and Miltefosine displayed low SI among the compounds. Pentamidine isethionate was effective at high concentrations, which was toxic. Miltefosine exhibited the lowest cytotoxicity; nevertheless, due to the lowest anti-Acanthamoeba activity presented a low selectivity against the parasite. Further studies on more clinical samples and prolonged incubation time should be done to investigate the effectiveness and toxicity of drugs in both in vitro and in vivo conditions.

Assessment of pathogenic potential of Acanthamoeba isolates by in vitro and in vivo tests

Acanthamoeba are free-living protozoa present ubiquitously in numerous environmental reservoirs that exist as an actively feeding trophozoite or a dormant cyst stage. The pathogenic Acanthamoeba are known to cause Acanthamoeba keratitis (AK) and granulomatous amoebic encephalitis (GAE). Despite their omnipresence, the number of infections is quite low. The reason behind this low frequency of Acanthamoeba infections could be the existence of many non-pathogenic strains or a successful host immune response to these infections. Studies in the past have proposed a few physiological parameters for the differentiation of pathogenic and non-pathogenic strains. Additionally, in vivo experiments are known to play an essential role in understanding the virulence of parasites, immunological aspects, and disease pathogenesis. The thermotolerance (30 °C, 37 °C, and 40 °C) and osmotolerance (0.5 M, 1 M, and 1.5 M) tests were performed on 43 Acanthamoeba isolates from patients with keratitis (n = 22), encephalitis (n = 5), and water samples (n = 16). In addition, the genotype of 10 Acanthamoeba isolates (keratitis (n = 2), encephalitis (n = 2), water (n = 6)) was determined and were then evaluated for pathogenicity on mouse model by inducing Acanthamoeba keratitis and amoebic encephalitis. The results of the thermotolerance and osmotolerance assays categorized 29/43 (67.4%) isolates as pathogenic, 8 as low pathogenic (18.6%), and the remaining 6 (13.9%) as non-pathogenic. The 10 Acanthamoeba isolates were categorized as T11 (5 isolates), T5 (2 isolates), T4 (2 isolates), and T10 (1 isolate) genotypes. Out of 10 Acanthamoeba isolates, 9 were successful in establishing AK, amoebic encephalitis, or both in the mice model, and a single isolate was found non-pathogenic. Two isolates from water samples were non-pathogenic in the physiological tests but successfully established Acanthamoeba infection in the mice model. The results of the physiological assays and in vivo experiments were analogous for 7 isolates while 1 isolate from the water was low pathogenic in the physiological assays but failed to produce pathogenicity during in vivo experiments. The physiological parameters are not very dependable to test the pathogenic potential of Acanthamoeba isolates, and thus results must always be validated by in vivo experiments. There is no infallible approach for determining the potential pathogenicity of environmental isolates of Acanthamoeba because several parameters regulate the pathogenic potential.

Successive Acanthamoeba Corneal Isolates Identified in Poland Monitored in Terms of In Vitro Dynamics

BACKGROUND

Amoebae of the genus Acanthamoeba cause a sight-threatening infection called Acanthamoeba keratitis. It is considered a rare disease in humans but poses an increasing threat to public health worldwide, including in Poland. We present successive isolates from serious keratitis preliminary examined in terms of the identification and monitoring of, among others, the in vitro dynamics of the detected strains.

METHODS

Clinical and combined laboratory methods were applied; causative agents of the keratitis were identified at the cellular and molecular levels; isolates were cultivated in an axenic liquid medium and regularly monitored.

RESULTS

In a phase-contrast microscope, Acanthamoeba sp. cysts and live trophozoites from corneal samples and in vitro cultures were assessed on the cellular level. Some isolates that were tested at the molecular level were found to correspond to A. mauritanensis, A. culbertsoni, A. castellanii, genotype T4. There was variability in the amoebic strain dynamics; high viability was expressed as trofozoites' long duration ability to intense multiply.

CONCLUSIONS

Some strains from keratitis under diagnosis verification and dynamics assessment showed enough adaptive capability to grow in an axenic medium, allowing them to exhibit significant thermal tolerance. In vitro monitoring that was suitable for verifying in vivo examinations, in particular, was useful to detect the strong viability and pathogenic potential of successive Acanthamoeba strains with a long duration of high dynamics.

The Status of Molecular Analyses of Isolates of Acanthamoeba Maintained by International Culture Collections

Acanthamoeba is among the most ubiquitous protistan groups in nature. Knowledge of the biological diversity of Acanthamoeba comes in part from the use of strains maintained by the major microbial culture collections, ATCC and CCAP. Standard strains are vital to ensure the comparability of research. The diversity of standard strains of Acanthamoeba in the culture collections is reviewed, emphasizing the extent of genotypic studies based on DNA sequencing of the small subunit ribosomal RNA from the nucleus (18S rRNA gene; Rns) or the mitochondria (16S-like rRNA gene; rns). Over 170 different strains have been maintained at some time by culture centers. DNA sequence information is available for more than 70% of these strains. Determination of the genotypic classification of standard strains within the genus indicates that frequencies of types within culture collections only roughly mirror that from clinical or environmental studies, with significant differences in the frequency of some genotypes. Culture collections include the type of isolate from almost all named species of Acanthamoeba, allowing an evaluation of the validity of species designations. Multiple species are found to share the same Sequence Type, while multiple Sequence Types have been identified for different strains that share the same species name. Issues of sequence reliability and the possibility that a small number of standard strains have been mislabeled when studied are also examined, leading to potential problems for comparative analyses. It is important that all species have reliable genotype designations. The culture collections should be encouraged to assist in completing the molecular inventory of standard strains, while workers in the Acanthamoeba research community should endeavor to ensure that strains representative of genotypes that are missing from the culture collection are provided to the culture centers for preservation.

Detection of Acanthamoeba spp. in groundwater sources in a rural area in the Philippines

Research on free-living amoebae (FLA) and its public health implication as an etiologic agent of parasitic infection in humans has recently gained traction in the Philippines. This study aimed to identify potential FLAs in collected groundwater samples from Masinloc, Zambales, Philippines. Fifty-four (54) water samples were collected in 250-mL sterile polyethylene containers by purposive sampling from selected groundwater sources in six (6) barangays of Masinloc. The samples were vacuum filtered through a 1.2-μm pore glass microfiber filter, cultured onto non-nutrient agar (NNA) lawned with Escherichia coli, and observed microscopically for amoebic growth for 14 days using light microscopy. Amoebic growth was observed in 11.1% (6/54) of water samples. DNAs from positive samples were extracted and were made to react with polymerase chain reaction using Acanthamoeba-specific JDP1 (5'-GGCCCAGATCGTTTACCGTGAA-3') and JDP2 (5'-TCTCACAAGCTGCTAGGGAGTCA-3') primers, and universal primer Euk A (5'-AACCTGGTTGATCCTGCCAGT-3') and Euk B (5'-TGATCCTTCTGCAGGTTCACCTAC-3'). The presence of Acanthamoeba genotypes T4, T7, and T11 was confirmed using molecular and phylogenetic analysis. Our results confirmed that groundwater sources from two of six sampling sites (33.3%) in Masinloc, Zambales, were contaminated with potentially pathogenic FLAs. Proper identification of risk factors that may cause contamination consequently leads to the implementation of programs that will prevent future infections.

Biological characteristics and pathogenicity of Acanthamoeba

Acanthamoeba is an opportunistic protozoa, which exists widely in nature and is mainly distributed in soil and water. Acanthamoeba usually exists in two forms, trophozoites and cysts. The trophozoite stage is one of growth and reproduction while the cyst stage is characterized by cellular quiescence, commonly resulting in human infection, and the lack of effective monotherapy after initial infection leads to chronic disease. Acanthamoeba can infect several human body tissues such as the skin, cornea, conjunctiva, respiratory tract, and reproductive tract, especially when the tissue barriers are damaged. Furthermore, serious infections can cause Acanthamoeba keratitis, granulomatous amoebic encephalitis, skin, and lung infections. With an increasing number of Acanthamoeba infections in recent years, the pathogenicity of Acanthamoeba is becoming more relevant to mainstream clinical care. This review article will describe the etiological characteristics of Acanthamoeba infection in detail from the aspects of biological characteristic, classification, disease, and pathogenic mechanism in order to provide scientific basis for the diagnosis, treatment, and prevention of Acanthamoeba infection.

In Vitro Cytopathogenic Activities of Acanthamoeba T3 and T4 Genotypes on HeLa Cell Monolayer

Amoebic keratitis and encephalitis are mainly caused by free-living amoebae of the genus Acanthamoeba, which consists of both pathogenic and nonpathogenic species. The global distribution, amphizoic properties and the severity of the disease caused by Acanthamoeba species have inspired the scientific community to put more effort into the isolation of Acanthamoeba, besides exploring the direct and indirect parameters that could signify a pathogenic potential. Therefore, this study was performed to characterize the pathogenic potential of Acanthamoeba isolated from contact lens paraphernalia and water sources in Malaysia. Various methodologies were utilized to analyze the thermotolerance and osmotolerance, the secretion level of proteases and the cytopathic effect of trophozoites on the cell monolayer. In addition, the in vitro cytopathogenicity of these isolates was assessed using the LDH-release assay. A total of 14 Acanthamoeba isolates were classified as thermo- and osmotolerant and had presence of serine proteases with a molecular weight of 45-230 kDa. Four T4 genotypes isolated from contact lens paraphernalia recorded the presence of serine-type proteases of 107 kDa and 133 kDa. In contrast, all T3 genotypes isolated from environmental samples showed the presence of a 56 kDa proteolytic enzyme. Remarkably, eight T4 and a single T3 genotype isolates demonstrated a high adhesion percentage of greater than 90%. Moreover, the use of the HeLa cell monolayer showed that four T4 isolates and one T3 isolate achieved a cytopathic effect in the range of 44.9-59.4%, indicating an intermediate-to-high cytotoxicity level. Apart from that, the LDH-release assay revealed that three T4 isolates (CL5, CL54 and CL149) and one T3 isolate (SKA5-SK35) measured an exceptional toxicity level of higher than 40% compared to other isolates. In short, the presence of Acanthamoeba T3 and T4 genotypes with significant pathogenic potential in this study reiterates the essential need to reassess the functionality of other genotypes that were previously classified as nonpathogenic isolates in past research.

Acanthamoeba Mannose and Laminin Binding Proteins Variation across Species and Genotypes

Acanthamoeba is a ubiquitous free-living amoeba capable of being an opportunistic pathogen in humans and animals. A critical step in infection is the adhesion of the amoeba to host cells and tissues, and two major parasite adhesins, mannose-binding protein (MBP) and laminin-binding protein (LBP), are known to recognize the cell surface glycoproteins and those of the extracellular matrix, respectively. In this study, the available genomes of Acanthamoeba were analysed to recover the sequences of MBP and LBP using previously published genetic data. Genes for both proteins were successfully obtained from strains belonging to various genotypes (T4A, T4D, T4G, T4F, T2, T5, T10, T22, T7 and T18), resulting in a single gene for LBP but identifying two types of MBP, MBP1 and MBP2. Phylogenetic analysis based on deduced amino acid sequences shows that both MBP and LBP have a branching pattern that is consistent with that based on 18S rDNA, indicating that changes in both proteins occurred during diversification of Acanthamoeba lines. Notably, all MBPs possess a conserved motif, shared with some bacterial C-type lectins, which could be the recognition site for mannose binding.

Efficacy of Off-Label Anti-Amoebic Agents to Suppress Trophozoite Formation of Acanthamoeba spp. on Non-Nutrient Agar Escherichia Coli Plates

Acanthamoeba keratitis (AK) is a dangerous infectious disease, which is associated with a high risk of blindness for the infected patient, and for which no standard therapy exists thus far. Patients suffering from AK are thus treated, out of necessity, with an off-label therapy, using drugs designed and indicated for other diseases/purposes. Here, we tested the capability of the off-label anti-amoebic drugs chlorhexidine (CH; 0.1%), dibromopropamidine diisethionate (DD; 0.1%), hexamidine diisethionate (HD; 0.1%), miltefosine (MF; 0.0065%), natamycin (NM; 5%), polyhexamethylene biguanide (PHMB; 0.02%), povidone iodine (PVPI; 1%), and propamidine isethionate (PD; 0.1%) to suppress trophozoite formation of Acantamoeba castellanii and Acanthamoeba hatchetti cysts on non-nutrient agar Escherichia coli plates. Of the eight off-label anti-amoebic drugs tested, only PVPI allowed for a complete suppression of trophozoite formation by drug-challenged cysts for all four Acanthamoeba isolates in all five biological replicates. Drugs such as NM, PD, and PHMB repeatedly suppressed trophozoite formation with some, but not all, tested Acanthamoeba isolates, while other drugs such as CH, DD, and MF failed to exert a relevant effect on the excystation capacities of the tested Acanthamoeba isolates in most, if not all, of our repetitions. Our findings suggest that pre-testing of the AK isolate with the non-nutrient agar E. coli plate assay against the anti-amoebic drug intended for treatment should be performed to confirm that the selected drug is cysticidal for the Acanthamoeba isolate.

The Risk Factors and Clinical Features of Acanthamoeba Keratitis: First Time Detection of Acanthamoeba T5 Genotype from Keratitis Patients in Turkey

PURPOSE

The primary aim of this study is to investigate Acanthamoeba in clinical samples of keratitis cases (n = 60), in contact lens (CL) and lens care solutions of asymptomatic CL users (n = 41), and to identify the genotypes in positive samples. The secondary aim is to assess the risk factors and clinical features of Acanthamoeba keratitis (AK) patients.

METHODS

All samples from patients and asymptomatic CL users were examined by microscopy and inoculated in non-nutrient agar plates. PCR was performed using the DNA isolated from corneal scrapings, CL and lens care solution samples. Positive DNA samples were sequenced to determine the genotype of Acanthamoeba.

RESULTS

In none of the samples, Acanthamoeba was identified by microscopy, while Acanthamoeba was detected in a patient with keratitis by culture method. However, Acanthamoeba was detected in 11.66% (7/60) of the keratitis patients by PCR. The genotypes of these isolates detected by sequencing were T4 (4), and T5 (3). Acanthamoeba was detected in none of the samples of asymptomatic CL users by any of the three methods.

CONCLUSION

To best of our knowledge, this is the first study to detect T5 genotype in AK patients from Turkey. In addition, the CL use was found to be an important risk factor for AK.

Surveillance of Amoebic Keratitis-Causing Acanthamoebae for Potential Bacterial Endosymbionts in Ontario, Canada

Acanthamoeba spp. are the causative pathogens of several infections, including amoebic keratitis (AK), a vision-threatening infection. Acanthamoebae from corneal specimens of patients with AK harbor bacterial endosymbionts, which may increase virulence. We sought to understand the spectrum of bacterial endosymbionts present in clinical isolates of Acanthamoeba spp. identified in our reference parasitology laboratory. Isolates of Acanthamoeba spp. obtained from our biobank of anonymized corneal scrapings were screened for potential endosymbionts by PCR using primer pairs detecting bacteria belonging to orders Chlamydiales, Rickettsiales, or Legionellales and pan16S primers. Three primer pairs specific to the 18s rRNA gene of Acanthamoeba spp. were used for the amplification of Acanthamoeba DNA used for sequencing. Sanger sequencing of all PCR products was performed, followed by BLAST analysis for species identification. We screened 26 clinical isolates of Acanthamoeba spp. for potential endosymbionts. Five isolates (19%) were found to contain bacterial DNA belonging to Legionellales. Three (11%) contained members of the Rickettsiales and Pseudomonas genticulata was detected in a Rickettsia-positive sample. One strain (4%) contained Neochlamydia hartmannellae, a member of the Chlamydiales order. Bacterial endosymbionts are prevalent in clinical strains of Acanthamoeba causing AK isolated from corneal scrapings. The demonstration of these organisms in clinical Acanthamoeba isolates supports a potential exploration of anti-endosymbiont therapeutics as an adjuvant therapy in the treatment of AK.

Detection of Acanthamoeba spp. using carboxylesterase antibody and its usage for diagnosing Acanthamoeba-keratitis

Contact lens usage has contributed to increased incidence rates of Acanthamoeba keratitis (AK), a serious corneal infection that can lead to blindness. Since symptoms associated with AK closely resemble those incurred by bacterial or fungal keratitis, developing a diagnostic method enabling rapid detection with a high degree of Acanthamoeba-specificity would be beneficial. Here, we produced a polyclonal antibody targeting the carboxylesterase (CE) superfamily protein secreted by the pathogenic Acanthamoeba and evaluated its diagnostic potential. Western blot analysis revealed that the CE antibody specifically interacts with the cell lysates and conditioned media of pathogenic Acanthamoeba, which were not observed from the cell lysates and conditioned media of human corneal epithelial (HCE) cells, Fusarium solani, Staphylococcus aureus, and Pseudomonas aeruginosa. High titers of A. castellanii-specific antibody production were confirmed sera of immunized mice via ELISA, and these antibodies were capable of detecting A. castellanii from the cell lysates and their conditioned media. The specificity of the CE antibody was further confirmed on A. castellanii trophozoites and cysts co-cultured with HCE cells, F. solani, S. aureus, and P. aeruginosa using immunocytochemistry. Additionally, the CE antibody produced in this study successfully interacted with 7 different Acanthamoeba species. Our findings demonstrate that the polyclonal CE antibody specifically detects multiple species belong to the genus Acanthamoeba, thus highlighting its potential as AK diagnostic tool.

Severe Keratitis Caused by Acanthamoeba Genotype T12 in Thailand: A Case Report

Acanthamoeba keratitis is predominantly caused by genotype T4. We report a case of severe keratitis caused by Acanthamoeba in a 39-year-old man who had prior accidental exposure to a corrosive chemical. The patient developed central full thickness ring infiltration and epithelial defect with hypopyon that required keratoplasty. The acanthamoebae isolated from the patient exhibited thermotolerance phenotype with the capability to grow well at ambient temperature and at 42°C. Analysis of a near complete 18S rRNA gene of this isolate revealed a distinct sequence that can be unequivocally assigned to genotype T12, a rare genotype incriminated in corneal infections.

Super aggregated amphotericin B with a thermoreversible in situ gelling ophthalmic system for amoebic keratitis treatment

Acanthamoeba spp. are the causative agents of a sight-threatening infection of the cornea known as Acanthamoeba keratitis (AK). Amphotericin B - deoxycholate (AB) is used in the treatment of infectious keratitis, however, its topical administration has side effects as blepharitis, iritis, and painful instillation. In this context, the preheating of AB can decrease its toxicity by the formation of super aggregates (hAB). hAB associated with a thermoreversible in situ gelling ophthalmic system is a promising option due to the latter biocompatibility, low toxicity, and high residence time on the ocular surface. Our objective was to develop a topical ocular formulation of hAB for the treatment of AK. After heating at 70°C for 20 min, hAB was incorporated into a thermoreversible gelling system. The amebicidal activity of AB and hAB was evaluated against trophozoites and cysts of A. castellanii (ATCC 50492) and a regional clinical isolate (IC01). The results showed that the preheating of AB did not change the pharmacological action of the drug, with the amebicidal effect of AB and hAB under trophozoites and cysts of Acanthamoeba spp. The thermoreversible system remained stable, allowing the increase of drug retention time. For assessment of cytotoxicity, HUVEC (ATCC® CRL-1730) cells were challenged with AB and hAB for 48h. Cell viability was assessed, and hAB did not show cytotoxicity for HUVEC cells. As far as we know this was the first study that showed the preheated AB associated with a thermoreversible in situ gelling ophthalmic system as a promising system for topical ocular topical administration of hAB for AK therapy.

Analysis of Acanthamoeba genotypes from public freshwater sources in Thailand reveals a new genotype, T23 Acanthamoeba bangkokensis sp. nov

A survey of Acanthamoeba in 100 public freshwater sources in 28 provinces across Thailand has identified 9 genotypes comprising T2/6, T3-T5, T9, T11, T12, T18 and a novel ‘T23’ among 131 isolates. Sequencing of the near complete 18S rRNA gene of Acanthamoeba of all isolates has shown that the most predominant genotype T4 found in 87 isolates (66.4%) contained 4 subtypes, i.e. T4A, T4B, T4C and T4F, while all isolates assigned to genotype T2/6 belonged to subtype B. Among intron-bearing genotypes, most isolates harbouring genotype T3 contained S516 introns, characterised by 3 distinct variants whilst all genotypes T4A and T5 were intronless. Identical 18S rRNA sequences of Acanthamoeba were identified across regions of the country and four isolates in this study shared the same sequences with those from remote nations, suggesting that some strains have reproductive success in diverse ecological niche. Nucleotide diversity of genotypes T2/6B, T3, T4, T9 and T11 in this study was significantly less than that among global isolates outside Thailand, implying that limited sequence diversity occurred within local populations. A remarkably higher level of nucleotide diversity in genotype T11 than those of other genotypes (0.041 vs. 0.012–0.024) could be due to cryptic subtypes. Recombination breakpoints have been detected within genotypes and subtypes as well as within isolates despite no evidence for sexual and parasexual cycles in the genus Acanthamoeba. Tajima’s D, Fu & Li’s D* and F* statistics revealed significantly negative deviation from neutrality across genotypes and subtypes, implying purifying selection in this locus. The 18S rRNA gene of the novel genotype ‘T23’ displayed 7.82% to 28.44% sequence differences in comparison with all known genotypes. Both Bayesian and maximum likelihood phylogenetic trees have placed genotype T23 as sister to the clade comprising genotypes T10, T12 and T14, all of these possess cyst structure belonging to morphological group III. Hence, Acanthamoeba bangkokensis sp. nov. is proposed for this novel genotype. It is likely that more genotypes of Acanthamoeba remain to be discovered while the evolution of the 18S rRNA gene of this pathogenic-free living amoeba seems to be ongoing.

On the diversity and clinical importance of Acanthamoeba spp. from Group 1

Group 1 acanthamoebae are morphologically and phylogenetically distinct from all other Acanthamoeba species. They include five species, each labelled by its genotype: A. astronyxis (T7), A. tubiashi (T8), A. comandoni (T9), unnamed Acanthamoeba sp. (T17), and A. byersi (T18). Thought only environmental, they have recently attracted attention due to their recovery in cases of human keratitis and encephalitis, the main diseases caused by Acanthamoeba, where the usual causative agents are mainly species of Groups 2 and 3. Analysis of the available data confirms the pathogenic importance of these species, although it is probably minor compared to that of the species in Groups 2 and 3. In addition, it should be noted that there are difficulties in identifying genotypes by widely used molecular methods, and some misidentifications are revealed.

Diagnosis of Acanthamoeba keratitis in Mashhad, Northeastern Iran: A Gene-Based PCR Assay

Background:

The genus Acanthamoeba is a free-living opportunistic protozoan parasite, which widely distributed in soil and fresh water. Acanthamoeba keratitis, which causes a sight-threating infection of the cornea, is going to rise in Iran and worldwide. The aim of this study was to compare direct microscopy, culture and PCR for detection of Acanthamoeba spp. in clinical samples and to determine the genotypes of Acanthamoeba spp. by sequencing 18SrRNA gene.

Methods:

Among patients clinically suspected to AK referred to a tertiary ophthalmology center at Mashhad, northeastern Iran. During 2017-18, twenty corneal scrapes specimens obtained. The samples were divided into three parts, subjected to direct microscopic examination, culture onto non-nutrient agar and PCR technique. Sensitivity, specificity, accuracy and likelihood ratio were evaluated.

Results:

Among 20 persons clinically suspected to amoebic keratitis, 13(69.2%) patients definitely diagnosed as Acanthamoeba keratitis. Wearing contact lens, eye trauma due to foreign particle and swimming in fresh water were the main predisposing factors. Most of patients suffered from pain and photophobia. Corneal ring infiltration and epithelial defect were common clinical sings. Direct examination had the lowest sensitivity and sensitivity of both Nelson-PCR and JDP-PCR methods were equal and highest. In addition, the results of sequencing identified that all strains belonged to T4 genotype.

Conclusion:

Amoebic keratitis is a sporadic parasitic keratitis, which is mainly seen in contact lens user in Mashhad. PCR based on 18S ribosomal DNA with JDP primers is a reliable and highly sensitive method for diagnosis of Acanthamoeba keratitis in clinically suspected cases.

Free-living amoebae and other neglected protistan pathogens: Health emergency signals?

Protistan parasites have an undisputed global health impact. However, outside of a few key exceptions, e.g. the agent of malaria, most of these infectious agents are neglected as important health threats. The Symposium entitled "Free-living amoebae and neglected pathogenic protozoa: health emergency signals?" held at the European Congress of Protistology in Rome, July 2019, brought together researchers addressing scientific and clinical questions about some of these fascinating organisms. Topics presented included the molecular basis of pathogenicity in Acanthamoeba; genomics of Naegleria fowleri; and epidemiology of poorly diagnosed enteric protistan species, including Giardia, Cryptosporidium, Blastocystis, Dientamoeba. The Symposium aim was to excite the audience about the opportunities and challenges of research in these underexplored organisms and to underline the public health implications of currently under-appreciated protistan infections. The major take home message is that any knowledge that we gain about these organisms will allow us to better address them, in terms of monitoring and treatment, as sources of future health emergencies.

Isolation and Identification of Pathogenic Acanthamoeba Species from Air Conditioning Systems, Egypt

Acanthamoeba are free-living amoebae that cause granulomatous amoebic encephalitis and keratitis. In this study, we aimed to isolate and identify Acanthamoeba from air conditioning systems using in vitro cell culture and polymerase chain reaction assays. We also estimated the pathogenicity of the isolates by measuring their thermotolerance and studying mice models inoculated with these isolates. Of the 80 dust samples acquired, 41 (51.25%) were found to be positive for Acanthamoeba spp. using in vitro cell culture and the results were validated using PCR. Out of these 41 samples, 27 (65.9%) were thermotolerant and 16 (39%) samples could infect mice and cause histopathological effects. Highly pathogenic Acanthamoeba isolates were characterized by their thermotolerance and the ability to disseminate in all organs after infection, causing early death of infected animals. Our study thus validated the presence of pathogenic isolates of Acanthamoeba in air conditioners that may be potentially infectious to humans.

Anti-Acanthamoeba disinfection: hands, surfaces and wounds

Acanthamoebae are facultative parasites causing rare but serious infections such as keratitis and encephalitis and are also known as vectors for several bacterial pathogens, including legionellae and pseudomonads. Acanthamoeba cysts are particularly resilient and enable the amoebae to withstand desiccation and to resist disinfection and therapy. While the search for new therapeutic options has been intensified in the past years, hand and surface disinfectants as well as topical antiseptics for preventing infections have not been studied in detail to date. The aim of this study was to screen well-known and commonly used antimicrobial products in various formulations and different concentrations for their efficacy against Acanthamoeba trophozoites and cysts, including aliphatic alcohols, quaternary ammonium compounds (QACs), peracetic acid (PAA), potassium peroxymonosulfate sulfate (PPMS) and octenidine dihydrochloride (OCT). Of all products tested, OCT and QACs showed the highest efficacy, totally eradicating both trophozoites and cysts within 1 min. The determined 50% effective concentration (EC₅₀) for cysts was 0.196 mg/mL for OCT and 0.119 mg/mL for QACs after 1 min of exposure. PAA and PPMS showed reliable cysticidal efficacies only with prolonged incubation times of 30 min and 60 min, respectively. Aliphatic alcohols generally had limited efficacy, and only against trophozoites. In conclusion, OCT and QACs are potent actives against Acanthamoeba trophozoites and cysts at concentrations used in commercially available products, within contact times suitable for surface and hand disinfection as well as topical antisepsis.

Species, Sequence Types and Alleles: Dissecting Genetic Variation in Acanthamoeba

Species designations within Acanthamoeba are problematic because of pleomorphic morphology. Molecular approaches, including DNA sequencing, hinted at a resolution that has yet to be fully achieved. Alternative approaches were required. In 1996, the Byers/Fuerst lab introduced the concept of sequence types. Differences between isolates of Acanthamoeba could be quantitatively assessed by comparing sequences of the nuclear 18S rRNA gene, ultimately producing 22 sequence types, designated T1 through T22. The concept of sequence types helps our understanding of Acanthamoeba evolution. Nevertheless, substantial variation in the 18S rRNA gene differentiates many isolates within each sequence type. Because the majority of isolates with sequences in the international DNA databases have been studied for only a small segment of the gene, designated ASA.S1, genetic variation within this hypervariable region of the 18S rRNA gene has been scrutinized. In 2002, we first categorized variation in this region in a sample of T3 and T4 isolates from Hong Kong, observing ten “alleles” within type T4 and five “alleles” within T3. Subsequently, confusion occurred when different labs applied redundant numerical labels to identify different alleles. A more unified approach was required. We have tabulated alleles occurring in the sequences submitted to the international DNA databases, and determined their frequencies. Over 150 alleles have occurred more than once within 3500+ isolates of sequence type T4. Results from smaller samples of other sequence types (T3, T5, T11 and T15, and supergroup T2/6) have also been obtained. Our results provide new insights into the evolutionary history of Acanthamoeba, further illuminating the degree of genetic separation between significant taxonomic units within the genus, perhaps eventually elucidating what constitutes a species of Acanthamoeba.

Validation of reference genes for the normalization of RT-qPCR gene expression in Acanthamoeba spp

Acanthamoebae are potentially pathogenic organisms, with a highly unique, yet still insufficiently investigated metabolism. Many open questions can be addressed by gene expression studies, however, for Acanthamoeba reliable standards have not yet been established. In this study, suitable reference genes (RGs) for RT-qPCR in Acanthamoeba were comprehensively evaluated, comparing different Acanthamoeba strains and employing four different algorithms (NormFinder, GeNorm, BestKeeper and RefFinder). Expression stability was assessed under various conditions and the potentials of the most promising RGs for accurate normalization of target genes were evaluated. Expression stability of RGs varied depending on conditions and employed algorithms, however, the genes for the 18S rRNA and the hypoxanthine phosphoribosyl transferase seem to be widely suitable RGs. Normalization with a combination of two carefully chosen RGs resulted in reliable expression data for target genes, while normalization with unsuitable RGs led to significant misinterpretation of expression profiles. Thus, a careful evaluation of RGs prior to expression studies is essential.

Isolation and identification of free-living amoeba from the hot springs and beaches of the Caspian Sea

Free-living amoeba (FLA) such as Acanthamoeba, Naegleria, Balamuthia, and Vermamoeba have been identified from both natural and human-made environments such as Hot springs and spa. Naegleria fowleri causes Primary Amoebic Meningoencephalitis (PAM), while Acanthamoeba and Balamuthia cause chronic granulomatous encephalitis. Acanthamoeba also can cause cutaneous lesions and Amoebic Keratitis (AK) that is associated with contact lens use or corneal trauma. FLA are known to serve as host of and vehicles for diverse intracellular organisms. This study aimed was to identify the presence of FLA in the hot springs and beaches of the Caspian Sea in Ramsar tourist town located in the northern part of Iran. Water samples were collected in sterile bottles and were transferred to the laboratory. One litre of each sample passed through the nitrocellulose membrane filter. Each filter insert was then placed in non-nutrient agar plates already seeded with lawn culture of Escherichia coli. Positive samples were analyzed by morphological keys and Polymerase chain reaction (PCR) using 18S rDNA gene and ITS region to identify amoeba isolates. A total of 81 water sampled were tasted. After identified using the morphological key and PCR assay, 54 (66.6%) of the samples were positive for FLA. Ten of the samples were identified as Acanthamoeba (belong to T3, T4, and T5 genotypes), three as Vermamoeba vermiformis, four as Naegleria (3 N.australiensis and 1 N.grubery). Only one sample was positive Vahlkampfia. The presence of thermotolerant FLA in the Hot springs and beaches of the Caspian Sea as places for recreational purposes or wellness may be a potential health risk.

Acanthamoeba spp. in river water samples from the Black Sea region, Turkey

The present study aims to investigate the occurrence of free living amoeba (FLA) in water resources (rivers and tap water) in Samsun in the Black Sea. The presence of Acanthamoeba spp. was confirmed in 98 of 192 water samples collected from 32 sites of Samsun province (Samsun centre, Terme, Carsamba, Tekkekoy, Bafra) by PCR. Acanthamoeba spp. were found in 15/36 river samples from Samsun, in 58/90 from Terme, in 12/30 from Carsamba, in 7/18 from Tekkekoy and in 6/18 from Bafra. No Acanthamoeba species were detected in tap water samples. The highest rate in river waters contaminated with Acanthamoeba species was in Terme followed by Samsun centre (41.7%), Carsamba (40%), Tekkekoy (38.9%) and Bafra districts (33.3%), respectively. The result of the subsequent sequence analysis showed Haplotype I (A. triangularis) in 5%, Haplotype II (A. polyphaga) in 29.6%, Haplotype III (Acanthamoeba spp.) in 62% and Haplotype IV (A. lenticulata) in 3%. The most common genotype was Acanthamoeba T4 (Acanthamoeba spp., A. polyphaga, A. triangularis) and T5 genotype was also found in 3%. The T4 genotype is the most common genotype associated with Acanthamoeba keratitis (AK) worldwide; therefore, humans and animals living in the area are at risk after contact with such waters.

Free-living amoebae and their relationship to air quality in hospital environments: characterization of Acanthamoeba spp. obtained from air-conditioning systems

Free-living amoebae (FLA) are widely dispersed in the environment, can cause opportunistic and non-opportunistic infections in humans and other animals. The aim of the present study was characterize FLA obtained from air-conditioners of a public hospital in the city of Florianópolis, SC, Brazil. Fifty-four dust samples were collected of air conditioners, and were inoculated on 1.5% non-nutrient agar, overlaid with layers of Escherichia coli. Subsequently the isolates were axenised in PYG growth medium. The morphological and molecular characterization of the isolates was performed, as well as the tolerance (physiological) assays were used to evaluate the pathogenic potential. The results revealed the presence of FLA in 42 (77.8%) of the collected samples. Of these, 39 (92.9%) axenic isolates of FLA were obtained for morphological and genotypic studies. All the isolates characterized belong to the genus Acanthamoeba. Nineteen (48.7%) isolates belong to the genotype T4, 16 (41.0%) to the T5 genotype and 4 (10.3%) to genotype T11. Seven (18.0%) isolates were considered potentially pathogenic in tolerance assays. These findings require attention, considering the isolation environment and immunocompromised characteristics of many hospitalized patients.

Isolation of Acanthamoeba T5 from Water: Characterization of Its Pathogenic Potential, Including the Production of Extracellular Vesicles

Acanthamoeba is a genus of free-living amoebae widely distributed in nature, associated with the development of encephalitis and keratitis. Despite the fact that it is common to find genotype T5 in environmental samples, only a few cases have been associated with clinical cases in humans. The wide distribution of Acanthamoeba, the characteristic of being amphizoic and the severity of the disease motivate researchers to focus on the isolation of these organisms, but also in demonstrating direct and indirect factors that could indicate a possible pathogenic potential. Here, we performed the characterization of the pathogenic potential of an Acanthamoeba T5 isolate collected from a water source in a hospital. Osmo- and thermotolerance, the secretion of proteases and the effect of trophozoites over cell monolayers were analyzed by different methodologies. Additionally, we confirm the secretion of extracellular vesicles (EVs) of this isolate incubated at two different temperatures, and the presence of serine and cysteine proteases in these vesicles. Finally, using atomic force microscopy, we determined some nanomechanical properties of the secreted vesicles and found a higher value of adhesion in the EVs obtained at 37 °C, which could have implications in the parasite´s survival and damaging potential in two different biological environments.

Detection of Acanthamoeba spp. from dust phenomenon in Ilam Province, West Iran

In recent years, increasing dust phenomenon in the west of Iran has led to social, economic, and health concerns. This study aimed to represent the existence and genotyping of Acanthamoeba spp. in dust phenomenon in Ilam Province, Iran. In this study, 55 dust samples were collected and by targeting the diagnostic fragment 3 region of the 18S rRNA gene, the genotypes were determined. Utilizing the tolerance ability test, the pathogenic potential of all positive isolates was also recognized. Eighteen samples of Acanthamoeba (32.7%) were detected in the sampling areas. According to sequencing analysis, the isolates related to T4 (77.7%) and T2 (22.3%) genotypes were reported. It was revealed by thermo- and osmotolerance tests in which six strains are extremely pathogenic. To our knowledge, the pathogenic Acanthamoeba was potentially isolated initially from dust phenomenon in Ilam Province. Thus, these strains are probably highly virulent, and dusts are possible sources of Acanthamoeba infection in humans.

Symbiont-Mediated Defense against Legionella pneumophila in Amoebae

Bacterial pathogens are generally investigated in the context of disease. To prevent outbreaks, it is essential to understand their lifestyle and interactions with other microbes in their natural environment. Legionella pneumophila is an important human respiratory pathogen that survives and multiplies in biofilms or intracellularly within protists, such as amoebae. Importantly, transmission to humans occurs from these environmental sources. Legionella infection generally leads to rapid host cell lysis. It was therefore surprising to observe that amoebae, including fresh environmental isolates, were well protected during Legionella infection when the bacterial symbiont Protochlamydia amoebophila was also present. Legionella was not prevented from invading amoebae but was impeded in its ability to develop fully virulent progeny and were ultimately cleared in the presence of the symbiont. This study highlights how ecology and virulence of an important human pathogen is affected by a defensive amoeba symbiont, with possibly major consequences for public health.

Legionella pneumophila is an important opportunistic pathogen for which environmental reservoirs are crucial for the infection of humans. In the environment, free-living amoebae represent key hosts providing nutrients and shelter for highly efficient intracellular proliferation of L. pneumophila, which eventually leads to lysis of the protist. However, the significance of other bacterial players for L. pneumophila ecology is poorly understood. In this study, we used a ubiquitous amoeba and bacterial endosymbiont to investigate the impact of this common association on L. pneumophila infection. We demonstrate that L. pneumophila proliferation was severely suppressed in Acanthamoeba castellanii harboring the chlamydial symbiont Protochlamydia amoebophila. The amoebae survived the infection and were able to resume growth. Different environmental amoeba isolates containing the symbiont were equally well protected as different L. pneumophila isolates were diminished, suggesting ecological relevance of this symbiont-mediated defense. Furthermore, protection was not mediated by impaired L. pneumophila uptake. Instead, we observed reduced virulence of L. pneumophila released from symbiont-containing amoebae. Pronounced gene expression changes in the presence of the symbiont indicate that interference with the transition to the transmissive phase impedes the L. pneumophila infection. Finally, our data show that the defensive response of amoebae harboring P. amoebophila leaves the amoebae with superior fitness reminiscent of immunological memory. Given that mutualistic associations between bacteria and amoebae are widely distributed, P. amoebophila and potentially other amoeba endosymbionts could be key in shaping environmental survival, abundance, and virulence of this important pathogen, thereby affecting the frequency of human infection.

Identification and Genotypic Characterization of Potentially Pathogenic Acanthamoeba Isolated from Tap Water in Wuxi, China

Members of genus Acanthamoeba are widely distributed in the environment. Some are pathogenic and cause keratitis and fatal granulomatous amoebic encephalitis. In this study, we isolated an Acanthamoeba CJW/W1 strain from tap water in Wuxi, Jiangsu Province, China. Its 18S rDNA was sequenced and a phylogenetic tree was constructed. The isolated cysts belonged to morphologic group II. Comparison of 18S rDNA sequences of CJW/W1 strain and other isolates showed high similarity (99.7%) to a clinical isolate Asp, KA/E28. A phylogeny analysis confirmed this isolate belonged to the pathogenic genotype T4, the most common strain associated with Acanthamoeba-related diseases. This is the first report of an Acanthamoeba strain isolated from tap water in Wuxi, China. Acanthamoeba could be a public health threat to the contact lens wearers and, therefore, its prevalence should be monitored.

In Vitro Evaluation of Adhesion of Two Acanthamoeba Strains to Cosmetic Contact Lenses

PURPOSE

To evaluate the factors affecting the adhesion of Acanthamoeba trophozoites to the surface of cosmetic contact lenses (CCLs).

METHODS

Acanthamoeba castellanii and A. hatchetti trophozoites were inoculated onto CCLs (hema copolymer [HM] [38.5% H2O], phemfilcon [PF] [55% H2O], polymacon [PM] [38% H2O], polyhema [PH] [%42 H2O], and hema [HM55] [55% H2O]), and the number of trophozoites adhered to the lens surfaces was assessed over time, that is, at 15 min, 1, and 24 hr. In addition, scanning electron microscopy (SEM) analysis of the lens surfaces was performed to evaluate the effect of lens surface topology on adhesion.

RESULTS

The number of amoeba adhered to the contact lens surface was found lower with PF and PH production materials, than lenses with HM, PM, and HM55 production materials (P<0.05). No significant difference was detected in amoebic strains adhered in all the contact lens types (P>0.05). No significant difference was found on average amoeba adhesion between contact lenses with hema production material but with different water contents (45%, 55%), to see the effect of water content on amoebic adhesion (P>0.05). As a result of SEM analysis, surface topology showed no effect on adhesion.

CONCLUSION

(1) Chemical composition of lenses seemed to be mostly responsible for the adhesion of Acanthamoeba. (2) Different numbers of trophozoites, obtained after the adhesion experiment, could also indicate that adherence capacity can also differ among Acanthamoeba species.

Acanthamoeba of three morphological groups and distinct genotypes exhibit variable and weakly inter-related physiological properties

Free-living amoeba of the genus Acanthamoeba can eventually act as parasites, causing infections in humans. Some physiological characteristics of Acanthamoeba have been related to the grade of pathogenicity, allowing inferences about the pathogenic potential. The main goal of this study was to characterize isolates of Acanthamoeba obtained in Brazil and evaluate properties associated with their pathogenicity. A total of 39 isolates obtained from keratitis cases (n = 16) and environmental sources (n = 23) were classified into morphological groups and genotyped by sequencing the 18S rDNA fragments ASA.S1 and GTSA.B1. Samples were also tested regarding their thermo-tolerance, osmo-tolerance, and cytopathogenicity in MDCK cells. Isolates were identified and classified as follows: group I (T17, T18); group II (T1, T3, T4, T11); and group III (T5, T15), with the predominance of genotype T4 (22/39). Clinical isolates were genotyped as T3 (1/16), T4 (14/16) and T5 (1/16). The majority of isolates (38/39) were able to grow at 37 °C, but tolerance to 40 °C was more frequent among environmental samples. The tolerance to 1 M mannitol was infrequent (4/39), with three of these corresponding to clinical samples. The variable ability to cause cytopathic effects was observed among isolates of distinct genotypes and origins. This study identified, for the first time, T1 and T18 in Brazil. It also indicated a weak association between the clinical origin of the isolates and tolerance to high temperatures, high osmolarity, and cytopathogenicity, demonstrating that some in vitro parameters do not necessarily reflect a higher propensity of Acanthamoeba to cause a disease.

Acanthamoeba-mediated cytopathic effect correlates with MBP and AhLBP mRNA expression

BACKGROUND

In recent years, the concern of Acanthamoeba keratitis has increased since the infection is often associated with contact lens use. Partial 18S rRNA genotypic identification of Acanthamoeba isolates is important to correlate with pathophysiological properties in order to evaluate the degree of virulence. This is the first report of genotypic identification for clinical isolates of Acanthamoeba from corneal scrapings of keratitis in Malaysia. This study is also the first to correlate the mRNA expression of MBP and AhLBP as virulent markers for axenic strains of Acanthamoeba.

RESULTS

In this study, ten clinical isolates were obtained from corneal scrapings. Rns genotype and intra-genotypic variation at the DF3 region of the isolates were identified. Results revealed that all clinical isolates belonged to the T4 genotype, with T4/6 (4 isolates), T4/2 (3 isolates), T4/16 (2 isolates) and one new genotype T4 sequence (T4/36), being determined. The axenic clinical isolates were cytopathogenic to rabbit corneal fibroblasts. MBP and AhLBP mRNA expression are directly correlated to Acanthamoeba cytopathic effect.

CONCLUSIONS

All ten Malaysian clinical isolates were identified as genotype T4 which is predominantly associated with AK. Measuring the mRNA expression of Acanthamoeba virulent markers could be useful in the understanding of the pathogenesis of Acanthamoeba keratitis.

Potentially pathogenic Acanthamoeba genotype T4 isolated from dental units and emergency combination showers

BACKGROUND

Acanthamoeba is the genus of free-living amoebae that is most frequently isolated in nature. To date, 20 Acanthamoeba genotypes have been described. Genotype T4 is responsible for approximately 90% of encephalitis and keratitis cases. Due to the ubiquitous presence of amoebae, isolation from environmental sources is not uncommon; to determine the clinical importance of an isolation, it is necessary to have evidence of the pathogenic potential of amoebae.

OBJECTIVE

The aim of this study was to physiologically characterise 8 Acanthamoeba T4 isolates obtained from dental units and emergency combination showers and to determine their pathogenic potential by employing different laboratory techniques.

METHODS

Eight axenic cultures of Acanthamoeba genotype T4 were used in pathogenic potential assays. Osmotolerance, thermotolerance, determination and characterisation of extracellular proteases and evaluation of cytopathic effects in MDCK cells were performed.

FINDINGS

All of the isolates were osmotolerant, thermotolerant and had serine proteases from 44-122 kDa. Two isolates had cytopathic effects on the MDCK cell monolayer.

MAIN CONCLUSION

The presence of Acanthamoeba T4 with pathogenic potential in areas such as those tested in this study reaffirms the need for adequate cleaning and maintenance protocols to reduce the possibility of infection with free-living amoebae.

Free-living amoebae and their associated bacteria in Austrian cooling towers: a 1-year routine screening

Free-living amoebae (FLA) are widely spread in the environment and known to cause rare but often serious infections. Besides this, FLA may serve as vehicles for bacterial pathogens. In particular, Legionella pneumophila is known to replicate within FLA thereby also gaining enhanced infectivity. Cooling towers have been the source of outbreaks of Legionnaires' disease in the past and are thus usually screened for legionellae on a routine basis, not considering, however, FLA and their vehicle function. The aim of this study was to incorporate a screening system for host amoebae into a Legionella routine screening. A new real-time PCR-based screening system for various groups of FLA was established. Three cooling towers were screened every 2 weeks over the period of 1 year for FLA and Legionella spp., by culture and molecular methods in parallel. Altogether, 83.3 % of the cooling tower samples were positive for FLA, Acanthamoeba being the dominating genus. Interestingly, 69.7 % of the cooling tower samples were not suitable for the standard Legionella screening due to their high organic burden. In the remaining samples, positivity for Legionella spp. was 25 % by culture, but overall positivity was 50 % by molecular methods. Several amoebal isolates revealed intracellular bacteria.

Acanthamoeba culbertsoni: Electron-Dense Granules in a Highly Virulent Clinical Isolate

The virulence of various amoebic parasites has been correlated with the presence of electron-dense granules (EDGs) in the cytoplasm of trophozoites. Here, we report the finding by transmission electron microscopy of a large number of EDGs in a recent culture of Acanthamoeba culbertsoni, isolated from a severe case of human keratitis. When this isolate was maintained in culture for 6 mo, the granules almost disappeared. However, after induction of mice brain lesions with the long-term cultured isolate, recovered amoebas had abundant EDGs. Trophozoites of the original isolate, or those recovered from experimental lesions, secreted EDGs into the medium when incubated with MDCK cells. To analyze a possible cytotoxic effect the conditioned medium was incubated with MDCK monolayers. After 5 h, the media containing EDGs produced opening of the tight junctions; at 24 h, cell viability was compromised, and at 48 h most of the cells were detached from the monolayer. In contrast, trophozoites in long-term cultures did not release EDGs to the medium during incubation with MDCK cells, and the corresponding conditioned medium did not have any effect on MDCK monolayers. Our observations further support the hypothesis that EDGs play a role in the cytopathogenic mechanisms of A. culbertsoni.

Optimized methods for Legionella pneumophila release from its Acanthamoeba hosts

BACKGROUND

Free-living amoebae (FLA) and particularly acanthamoebae serve as vehicles and hosts for Legionella pneumophila, among other pathogenic microorganisms. Within the amoebae, L. pneumophila activates a complex regulatory pathway that enables the bacteria to resist amoebal digestion and to replicate. Moreover, the amoebae provide the bacteria protection against harsh environmental conditions and disinfectants commonly used in engineered water systems. To study this ecological relationship, co-culture and infection models have been used. However, there is a lack of data regarding the effectiveness of the different methods used to release intracellular bacteria from their amoebal hosts. The aim of this study was to evaluate the impact of the methods used to release intracellular L. pneumophila cells on the culturability of the bacteria. Furthermore, the standard method ISO 11731:1998 for the recovery and enumeration of Legionella from water samples was evaluated for its suitability to quantify intracellular bacteria.

RESULTS

The effectiveness of the eight release treatments applied to L. pneumophila and Acanthamoeba strains in a free-living state varied between bacterial strains. Moreover, the current study provides numerical data on the state of co-culture suspensions at different time points. The release treatments enhanced survival of both microorganisms in co-cultures of L. pneumophila and Acanthamoeba. Passage through a needle (21G, 27G) and centrifugation at 10,000 × g showed the highest bacterial counts when releasing the bacteria from the intracellular state. Regarding the ISO 11731:1998 method, one of the tested strains showed no differences between the recovery rates of associated and free-living L. pneumophila. However, a reduced bacterial recovery rate was observed for the second L. pneumophila strain used, and this difference is likely linked to the survival of the amoebae.

CONCLUSIONS

Mechanical release treatments were the most effective methods for providing bacterial release without the use of chemicals that could compromise further study of the intracellular bacteria. The current results demonstrated that the recovery of L. pneumophila from water systems may be underestimated if protozoal membranes are not disrupted.