Genotypic, phenotypic, biochemical, physiological and pathogenicity-based categorisation of Acanthamoeba strains

First Report of Acanthamoeba Genotype T4 from the Newly Formed Tajogaite Volcano Tephra (La Palma, Canary Islands)

The Tajogaite Volcano erupted on the western slope of the Cumbre Vieja mountain range on La Palma Island in the Canary Islands, Spain, in 2021. As one of the multiple consequences of this eruption, a layer of tephra was deposited, to a variable extent, over a large part of the island. Tephra deposits affect all aspects of vegetation recovery, the water cycle, and the long-term availability of volcanic nutrients. Protozoa, including free-living amoeba (FLA), are known to be among the first microorganisms capable of colonizing harsh environments. In the present study, the presence of FLA has been evaluated in the Tajogaite Volcano deposits. Samples of the tephra were collected and incubated at 26 °C on 2% non-nutrient agar plates with a layer of heat-killed E. coli. Morphological features, as well as the DF3 region sequence of the 18S rDNA, confirmed the presence of a T4 genotype strain of Acanthamoeba. Thermotolerance and osmotolerance assays were used to evaluate the strain's pathogenic potential. This strain was considered thermotolerant but poorly osmotolerant. To the best of our knowledge, this is the first report of Acanthamoeba being isolated from a recently erupted volcano.

Molecular characterisation and potential pathogenicity analysis of Acanthamoeba isolated from recreational lakes in Peninsular Malaysia

The present study aims to identify the Acanthamoeba genotypes and their pathogenic potential in three recreational lakes in Malaysia. Thirty water samples were collected by purposive sampling between June and July 2022. Physical parameters of water quality were measured in situ while chemical and microbiological analyses were performed in the laboratory. The samples were vacuum filtered through nitrate filter, cultured onto non-nutrient agar and observed microscopically for amoebic growth. DNAs from positive samples were extracted and made to react with polymerase chain reaction using specific primers. Physiological tolerance tests were performed for all Acanthamoeba-positive samples. The presence of Acanthamoeba was found in 26 of 30 water samples by PCR. The highest rate in lake waters contaminated with amoeba was in Biru Lake (100%), followed by Titiwangsa Lake (80%) and Shah Alam Lake (80%). ORP, water temperature, pH and DO were found to be significantly correlated with the presence of Acanthamoeba. The most common genotype was T4. Temperature- and osmo-tolerance tests showed that 8 (30.8%) of the genotypes T4, T9 and T11 were highly pathogenic. The presence of genotype T4 in habitats related to human activities supports the relevance of this amoeba as a potential public health concern.

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.

Acanthamoeba species isolated from marine water in Malaysia exhibit distinct genotypes and variable physiological properties

The present study identifies the Acanthamoeba genotypes and their pathogenic potential in five marine waters in Malaysia. Fifty water samples were collected between January and May 2019. Physical parameters of water quality were measured in situ, whereas chemical and microbiological analyses were conducted in the laboratory. All samples had undergone filtration using nitrocellulose membrane and were tested for Acanthamoeba using cultivation and polymerase chain reaction by targeting the 18S ribosomal RNA gene. The pathogenic potential of all positive isolates was identified using physiological tolerance tests. Thirty-six (72.0%) samples were positive for Acanthamoeba. Total coliforms (p = 0.013) and pH level (p = 0.023) displayed significant correlation with Acanthamoeba presence. Phylogenetic analysis showed that 27 samples belonged to genotype T4, four (T11), two (T18) and one from each genotype T5, T15 and T20. Thermo- and osmo-tolerance tests signified that three (8.3%) Acanthamoeba strains displayed highly pathogenic attributes. This study is the first investigation in Malaysia describing Acanthamoeba detection in marine water with molecular techniques and genotyping. The study outcomes revealed that the marine water in Malaysia could be an integral source of Acanthamoeba strains potentially pathogenic in humans. Thus, the potential risk of this water should be monitored routinely in each region.

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.

Isolation and identification of free-living amoebae isolated from well water in Istanbul

Free-living amoebae (FLA) are ubiquitous protozoa commonly found in water and soil environments. FLA belonging to various genera, including Acanthamoeba, Balamuthia, Naegleria, and Vermamoeba, can cause opportunistic and non-opportunistic infections in humans and animals such as keratitis or meningoencephalitis. In addition, some of them serve as hosts for a large number of pathogenic bacteria, yeasts, and viruses. The purpose of the present study was to assess the prevalence and molecular characterization of FLA in well water samples in İstanbul. Ten well water samples were collected from the taps and the presence of FLA was monitored both by the culture and polymerase chain reaction methods. FLA were isolated in 8 out of the 10 samples (80%) included in this study. Morphological analysis and partial sequencing of the 18S rDNA revealed the presence of Acanthamoeba genotypes T3 and T4, and Vermamoeba vermiformis in the investigated well water samples. This study reports for the first time the detection of Acanthamoeba genotype T3 in well water samples in İstanbul. The presence of potentially pathogenic amoebae in habitats related to human activities supports the relevance of FLA as a potential public health concern.

Update on Acanthamoeba phylogeny

The evolutionary history of Acanthamoeba has been substantially resolved by the 18S rDNA phylogeny which made it possible to delimit the main lines associated with some classical species. Some of them have proven to be polyphyletic, but the inappropriate use of treating under the same names unrelated strains persists. In this study, phylogenies based on the complete genes of nuclear and mitochondrial rDNA were compared, in order to verify the congruence of the different lines. Various groups can thus be identified, some of which associated with the type strains of given species. Recognizing them only by their species names would significantly reduce the current confusion, in addition to logically following basic taxonomic rules. In this manner, the well-known polyphyletic taxa A. castellanii and A. polyphaga, are restricted to the two lines specified by their type strains, while other widely used strains like Neff and Linc-AP1 that are often confused with the previous ones, can be assigned to their own lines. New species are potentially present in other groups and additional efforts are needed to delimit them.

Occurrence and molecular characterisation of Acanthamoeba isolated from recreational hot springs in Malaysia: evidence of pathogenic potential

This study aimed to identify the Acanthamoeba genotypes and their pathogenic potential in five recreational hot springs in Peninsular Malaysia. Fifty water samples were collected between April and September 2018. Physical parameters of water quality were measured in situ while chemical and microbiological analyses were performed in the laboratory. All samples were filtered through the nitrocellulose membrane and tested for Acanthamoeba using both cultivation and polymerase chain reaction (PCR) by targeting the 18S ribosomal RNA gene. The pathogenic potential of all positive isolates was identified using thermo- and osmotolerance tests. Thirty-eight (76.0%) samples were positive for Acanthamoeba. Water temperature (P = 0.035), chemical oxygen demand (P = 0.026), sulphate (P = 0.002) and Escherichia coli (P < 0.001) were found to be significantly correlated with the presence of Acanthamoeba. Phylogenetic analysis revealed that 24 samples belonged to genotype T4, nine (T15), two (T3) and one from each genotype T5, T11 and T17. Thermo- and osmotolerance tests showed that 6 (15.79%) of the Acanthamoeba strains were highly pathogenic. The existence of Acanthamoeba in recreational hot springs should be considered as a health threat among the public especially for high-risk people. Periodic surveillance of hot spring waters and posting warning signs by health authorities is recommended to prevent disease related to pathogenic Acanthamoeba.

Isolation and molecular identification of Acanthamoeba spp. from hot springs in Mazandaran province, northern Iran

Acanthamoeba is a free-living protozoan that can be found in natural and artificial environments such as hot tubs, surface water and springs and can cause severe diseases including amoebic keratitis and granulomatous amoebic encephalitis. The present study was conducted owing to the lack of research regarding genotypes of Acanthamoeba in hot springs of Mazandaran province in northern Iran. Twenty-four water samples were collected from all hot springs in Mazandaran province. After filtration through nitrocellulose membrane, samples were cultured on non-nutrient agar medium enriched with TYIS-33. The cultures were microscopically examined for the presence of Acanthamoeba. Positive cultures were analysed by polymerase chain reaction (PCR) and genotypes were determined by targeting the 18 S rRNA gene. The pathogenic potential of all positive isolates was identified using thermotolerance and osmotolerance tests. Eleven (47.8%) samples were positive for Acanthamoeba. Based on sequencing analysis, 100% of isolates belonged to the T4 genotype. Thermo- and osmo-tolerance tests showed that four (36.3%) Acanthamoeba strains were highly pathogenic. According to our research, the occurrence of Acanthamoeba in recreational hot springs could be a hazard for high risk persons. Posting warning signs and regular monitoring of these waters by health planners may therefore be useful for decreasing Acanthamoeba spp. infections.

Experimental infection of T4 Acanthamoeba genotype determines the pathogenic potential

T4 is the Acanthamoeba genotype most related to cases of granulomatous amoebic encephalitis (GAE) in immunocompromised patients and of keratitis in contact lens wearers. The determination of the pathogenic potential of Acanthamoeba clinical and environmental isolates using experimental models is extremely important to elucidate the capacity of free-living organisms to establish and cause disease in hosts. The aim of this study was to compare and evaluate the histopathology and culture between two different routes of experimental infection of T4 Acanthamoeba isolated from environmental and clinical source in mice (intracranial and intraperitoneal). Swiss isogenic healthy mice were inoculated with 10(4) trophozoites by intracranial (IC) and intraperitoneal (IP) routes and observed during 21 days. The brains from animals inoculated by the IC route were collected and from the animals of the IP inoculation group, the brains, livers, kidneys, spleens, and lungs were removed. The organs were prepared and appropriately divided to be evaluated with histopathology and culture. There was no significant difference between the inoculation routes in terms of isolates recovery (χ(2) = 0.09; p = 0.76). In the IC group, isolate recovery rate was significantly higher in histopathology than the one achieved by culture (χ(2) = 6.45; p < 0.01). Experimental infection revealed that all isolates inoculated could be considered invasive because it was possible to recover evolutive forms of Acanthamoeba in both routes. This work represents the first in vivo pathogenicity assay of primary isolation source in Central region of Brazil showing in vivo pathogenicity and hematogenous spread capacity of these protozoa, improving the knowledge on free-living amoebae isolates.

Isolation and identification of Acanthamoeba spp. from thermal swimming pools and spas in Southern Brazil

Free-living amoebae (FLA) are widely distributed in soil and water. A few number of them are implicated in human disease: Acanthamoeba spp., Naegleria fowleri, Balamuthia mandrillaris and Sappinia diploidea. Species of Acanthamoeba can cause keratitis and brain infections. In this study, 72 water samples were taken from both hot tubs and thermal swimming pools in the city of Porto Alegre, RS, Brazil, to determine the presence of Acanthamoeba in the water as well as perform the phenotypic and genotypic characterization of the isolates. The identification of the isolates was based on the cysts morphology and PCR amplification using genus-specific oligonucleotides. When the isolates were submitted to PCR reaction only 8 were confirmed as belonging to the genus Acanthamoeba. The sequences analysis when compared to the sequences in the GenBank, showed genotype distribution in group T3 (12,5%), T5 (12,5%), T4 (25%) and T15 (50%). The results of this study confirmed the presence of potentially pathogenic isolates of free living amoebae in hot swimming pool and spas which can present risks to human health.

Novel Acanthamoeba 18S rRNA gene sequence type from an environmental isolate

The free-living amoebae, Acanthamoeba, can act as opportunistic parasites on a wide range of vertebrates and are becoming a serious threat to human health due to the resistance of their cysts to harsh environmental conditions, disinfectants, some water treatment practices, and their ubiquitous distribution. Subgenus classification based on morphology is being replaced by a classification based on the sequences of the 18S rRNA gene with a total of 18 different genotypes (T1-T18). A new environmental strain of Acanthamoeba isolated from a waste water treatment plant is presented in this study as a candidate for the description of the novel genotype T19 after phylogenetic analysis.

Characterization of isolates of Acanthamoeba from the nasal mucosa and cutaneous lesions of dogs

Acanthamoeba spp. are free-living amoebae that are ubiquitously distributed in the environment and can cause encephalomyelitis in animals and humans. The factors that contribute to Acanthamoeba infections include parasite biology, genetic diversity, environmental spread, and host susceptibility. The aim of the present study was to characterize isolates of Acanthamoeba from the nasal mucosa and cutaneous lesions of dogs in order to access the occurence and pathogenicity of these organisms in this animal group. We studied 13 isolates of Acanthamoeba confirmed by polymerase chain reaction. They were sequenced, the genotype was determined, and their potential of pathogenicity was evaluated.

Physiological, morphological, and immunochemical parameters used for the characterization of clinical and environmental isolates of Acanthamoeba

The factors that characterize Acanthamoeba strains as harmless or potentially pathogenic have not been elucidated. Analysing the in vitro and in vivo parameters of Acanthamoeba samples, including heat tolerance at temperatures close to that of the human body, cytopathic effects, and their ability to cause infections in animals, has been proposed to identify their pathogenic potential. Another promising criterion for differentiating strains is the analysis of their biochemical and immunochemical properties. In this study, a comparative evaluation between clinical and environmental Acanthamoeba isolates was performed on the basis of physiological, morphological, and immunochemical criteria. Crude antigens were used to characterize the protein profiles by electrophoresis and immunize mice to produce polyclonal and monoclonal antibodies. The antibodies were characterized using ELISA, Western blotting, and immunofluorescence techniques. The results obtained with polyclonal antibodies suggest the presence of specific proteins for each studied isolate and co-reactive immunochemical profiles among conserved components. Ten monoclonal antibody clones were obtained; mAb3 recognized 3 out of 4 samples studied. The results of this study may help standardize criteria for identifying and characterizing Acanthamoeba strains. Taken together, our results support the view that a set of features may help differentiate Acanthamoeba species and isolates.

Prevalence of Acanthamoeba spp. (Sarcomastigophora: Acanthamoebidae) in wild populations of Aedes aegypti (Diptera: Culicidae)

Studies of interrelationship between microorganisms and mosquitoes are of great importance, since it can provide support for better understand related to biology, development and their control. In this way, it is known that mosquito larvae and free-living amoebae (FLA) normally occupy similar aquatic microhabitats. However, few studies have been conducted about such coexistence. For that reason, the objective of the present study was to verify the prevalence of Acanthamoeba spp. in wild populations of Aedes aegypti, as well as to characterize the genotypic lineage, and their possible pathogenicity through thermo- and osmotolerance. Amoebae were investigated in 60 pools, each containing ten larvae of A. aegypti, collected in Porto Alegre (Rio Grande do Sul, Brazil). The Acanthamoeba isolates were morphologically characterized and submitted to the polymerase chain reaction technique to confirm identification of the genus. In addition, genotype analyses as well as tests for presumptive pathogenicity in some samples were performed. Of the 60 pools examined, 54 (90 %) were positive for FLA. Of these isolates, 47 (87 %) belonged to the genus Acanthamoeba. The genotypic groups T4, T3 and T5 were identified, numbering 14 (53.8 %), ten (38.5 %) and two (7.7 %) isolates, respectively. The physiological tests performed with 14 strains showed that 12 (85.7 %) were non-pathogenic, while two (14.3 %) were considered as having low pathogenic potential. These results provide a basis for a better understanding of the interaction between these protozoan and mosquitoes in their natural habitat. This study is the first to report the isolation of Acanthamoeba spp. from wild mosquitoes.

Occurrence and characterization of Acanthamoeba similar to genotypes T4, T5, and T2/T6 isolated from environmental sources in Brasília, Federal District, Brazil

Species of Acanthamoeba can cause keratitis and brain infections. The characterization of environmental isolates is necessary to analyze the risk of human infection. We aimed at identifying and genotyping Acanthamoeba isolates from soil, swimming pools, and water features in Brasília, Federal District, Brazil, as well as determining their physiological characteristics and pathogenic potential. Among the 18 isolates studied, eight were similar to genotype T5, five to T4, and one to T2/T6, classified by the sequence analysis of 18S rDNA. Genotypes of four isolates were not determined. Ten isolates (55%) grew at 37 °C and seven (39%) grew in media with 1.5M mannitol, which are the physiological parameters associated with pathogenic Acanthamoeba; also, four isolates from swimming pools presented high pathogenic potential. Our results indicate a widespread distribution of potentially pathogenic Acanthamoeba T4, T5, and T2/T6 in different environmental sources in Brasília, revealing the potential risk of human infection and the need of preventive measures.

Potentially pathogenic free-living amoebae (FLA) isolated in Spanish wastewater treatment plants

This work studies the characterization of pathogenic free-living amoebae (FLA) from sewage effluents. Some of them, such as Acanthamoeba, Naegleria, Hartmannella, Sappinia, Balamuthia and Paravahlkampfia have been reported as a cause of diseases in humans. Therefore, the study of their habitats and their pathogenicity has become necessary. The population of potentially pathogenic FLA was analysed in five Spanish wastewater treatment plants. Five of the seven FLA isolated were identified as genus Acanthamoeba genotypes T3, T4, T7 and T9. Hartmannella and Naegleria were also isolated. Acanthamoeba demonstrated great thermotolerance and osmotolerance. It was also observed that treatment with sodium hypochlorite showed no significative reduction in the number of amoeba at concentrations of 0-100 ppm. The high resistance of FLA cysts to disinfection methods is a trojan horse for public health insofar as they colonize water systems and allow the survival of intracellular microorganisms resistant to FLA. The results of this work advance current knowledge of the FLA population.

Prevalence of acanthamoeba from tap water in rio grande do Sul, Brazil

A total of 136 samples of tap water were collected from state and municipal schools between March and November 2009. The samples were filtered through cellulose nitrate membranes that were seeded at non-nutrient agar 1.5% containing an overlayer of Escherichia coli suspension. Thirty-one (22.79%) tap water samples investigated were found positive for free-living amoebae (FLA). From these, 13 presented as FLA that seems to belong to the genus Acanthamoeba. All samples of FLA were cloned and identified as belonging to the genus Acanthamoeba by the morphology of cysts and trophozoites and by PCR using genus-specific primers that amplify the ASA.S1 region of 18S rDNA gene. Physiological tests of thermotolerance and osmotolerance were used to evaluate the pathogenicity of the isolates. The sequencing analysis by comparing the sequences submitted to GenBank, showed genotype distribution into groups T2, T2/T6, T6, and T4. In tests of thermotolerance and osmotolerance, 50% of the isolates had a low pathogenic potential. The results indicated the presence of Acanthamoeba in tap water in Rio Grande do Sul, Brazil, revealing its importance and the need for more epidemiological studies to determine their distribution in the environment and its pathogenic potential.

Acanthamoeba T3, T4 and T5 in swimming-pool waters from Southern Brazil

Species of Acanthamoeba, known to cause keratitis (AK) and granulomatous encephalitis in humans are frequently isolated from a variety of water sources. In this study, 13 Acanthamoeba isolates from swimming pools were classified at the genotype level based on the sequence analysis of the Acanthamoeba small-subunit rRNA gene. Nine of the 13 isolates were genotype T5, three were genotype T4, and one was T3. Several genotypes have been reported worldwide as causative agents of AK, including genotypes T3, T4, and T5. The present study indicates that genotype T5 is a common contaminant in swimming-pool water.

Isolation and characterization of Acanthamoeba spp. from air-conditioners in Kuala Lumpur, Malaysia

During a study on the quality of the indoor environment, Acanthamoeba spp. were detected in 20 out of 87 dust samples collected from air-conditioners installed in a four-story campus building located in Kuala Lumpur, Malaysia. Twenty-one cloned Acanthamoeba isolates designated as IMU1 to IMU21 were established from the positive primary cultures. Five species were identified from the 16 isolates according to the morphological criteria of Pussard and Pons; i.e. A. castellanii, A. culbertsoni, A. griffini, A. hatchetti and A. polyphaga. Species identities for the remaining five isolates (IMU4, IMU5, IMU15, IMU20 and IMU21), however, could not be determined morphologically. At genotypic characterization, these isolates were placed into T3 (IMU14); T5 (IMU16 and IMU17) and T4 (all the remaining isolates). To predict the potential pathogenicity of these Acanthamoeba isolates, thermo- and osmotolerance tests were employed; many isolates were predicted as potential human pathogens based on the outcome of these tests. This is the first time potentially pathogenic Acanthamoeba have been isolated from air-conditioners in Malaysia.

Potentially pathogenic acanthamoeba isolated from a hospital in Brazil

Studies on free-living amoebae (FLA), has been increased in recent years, especially related to the genus Acanthamoeba, because these organisms are widely found in the environment. The present work isolated and characterized this organism from biofilms and dust in hospital environment. 135 samples were collected in 15 different environments in a hospital at the south of Brazil. Thirty-one (23%) isolates were identified as morphologically belonging to the Acanthamoeba genus and 10 of these were submitted to temperature and osmotolerance tests as criterion for evaluation of the viability and pathogenicity. The tests indicate that four (40%) of these isolates could be potentially pathogenic because grew at high temperature (40 degrees C) and osmolarity (mannitol 1 M). Some isolates genotypes were determined after ribosomal DNA sequencing. These data revealed that three dust isolates belong to T4, two biofilm isolates to T5 and one dust isolate to T3 genotype. Therefore, Acanthamoeba found in the hospital environment represents a risk for people that circulate there.

Acanthamoeba castellanii: high antibody prevalence in racially and ethnically diverse populations

Acanthamoeba is an opportunistic protozoan pathogen that can produce keratitis and rare but fatal encephalitis. In the present study, we examined secretory IgA antibody to Acanthamoeba castellanii of the T4 genotype in mucosal secretions from 114 individuals of 37 countries, inhabitants and/or visitors, aged 16-65 years in London, UK. Acanthamoeba antibody prevalence rate was more than 85%, without any significant differences between males (86.2%) and females (89.2%). Some epidemiological factors contributing to the high prevalence of antibody to Acanthamoeba in surveyed population are discussed further.

Emerging Chlamydial Infections

Chlamydiae are important intracellular bacterial pathogens of vertebrates. In the last years, novel members of this group have been discovered: Parachlamydia acanthamoebae and Simkania negevensis seems to be emerging respiratory human pathogens, while Waddlia chondrophila might be a new agent of bovine abortion. Various species have been showed to infect also the herpetofauna and fishes, and some novel chlamydiae are endosymbionts of arthropods. In addition, molecular studies evidenced a huge diversity of chlamydiae from both environmental and clinical samples, most of such a diversity could be formed by novel lineages of chlamydiae. Experimental studies showed that free-living amoebae may support multiplication of various chlamydiae, then could play an important role as reservoir/vector of chlamydial infections. Here we reviewed literature data concerning chlamydial infections, with a particular emphasis on the novely described chlamydial organisms.

Isolation of potentially pathogenic strains of Acanthamoeba in wild squirrels from the Canary Islands and Morocco

In this study, a survey was conducted in order to determine the presence and pathogenic potential of free-living amoebae of Acanthamoeba genus in a population of Barbary Ground squirrels in Fuerteventura Island (Canary Islands, Spain) and Morocco. Identification of Acanthamoeba was based on the morphology of cyst and trophozoite forms and PCR amplification with a genus specific primer pair. The pathogenic potential of Acanthamoeba isolates was characterized using PCRs with two primer pairs related to Acanthamoeba pathogenesis and cytotoxicity assays using human corneal cells. Isolates genotypes were also determined after ribosomal DNA sequencing. These data revealed that the potentially pathogenic isolates belonged to T3 and T4. To our knowledge, this is the first report presenting the isolation of potentially pathogenic Acanthamoeba strains in wild squirrels, and it is also the first description of the pathogenic T3 and T4 Acanthamoeba genotypes in Fuerteventura and Morocco.

Acanthamoeba isolates belonging to T1, T2, T3, T4 and T7 genotypes from environmental freshwater samples in the Nile Delta region, Egypt

The free-living amoebae of the genus Acanthamoeba include non-pathogenic and pathogenic species and has been recently classified into 15 different genotypes, T1-T15. In this study, a survey was conducted in order to determine the presence and pathogenic potential of free-living amoebae of Acanthamoeba genus in freshwater sources associated with human activities in the Nile Delta region, Egypt. Identification of Acanthamoeba was based on the morphology of cyst and trophozoite forms and PCR amplification with a genus specific primer pair. The pathogenic potential of Acanthamoeba isolates was characterized using temperature and osmotolerance assays and PCR reactions with two primer pairs specific to Acanthamoeba pathogenesis. Isolates genotypes were also determined after ribosomal DNA sequencing. These data revealed that isolates belong to T1, T2, T3, T4 and T7 genotypes. As expected, T4 isolates exhibited the most pathogenic traits and were osmotolerant, temperature tolerant and expressed extracellular serine proteases. This is the first report presenting environmental distribution of Acanthamoeba genotypes in Egypt.

Pathogenic Acanthamoeba strains from water sources in Jamaica, West Indies

In 2004, samples of tap water and of river and sea water associated with human activities were collected in Jamaica, West Indies, and checked for free-living Acanthamoeba. The morphologies of the cysts and trophozoites observed and the results of PCR-based amplifications with a genus-specific primer pair were used to identify the Acanthamoeba isolates. The potential of each isolate as a human pathogen was then evaluated using thermotolerance and osmotolerance assays and two PCR-based assays for Acanthamoeba pathogenesis. Acanthamoeba were identified in 36.1%, 26.4% and 49.6% of the tap-, river- and sea-water samples collected, respectively. Pathogenic potential was shown by 60.0% of the Acanthamoeba strains isolated from tap water, 68.4% of the strains from river water, and 40.4% of the seawater strains. Sequencing of ribosomal DNA revealed the T1, T2, T4, T5, T7, T9 and T11 genotypes. Isolates of the T4 genotype were collected from tap, rain and sea water and, as expected, exhibited the most pathogenic traits; most were osmotolerant, thermotolerant and expressing extracellular serine protease. This is the first study of the occurrence and distribution of Acanthamoeba in water in the West Indies, and the results confirm the presence of potentially pathogenic strains in Jamaica.

Acanthamoeba genotype T4 from the UK and Iran and isolation of the T2 genotype from clinical isolates

The majority of the keratitis-causing Acanthamoeba isolates are genotype T4. In an attempt to determine whether predominance of T4 isolates in Acanthamoeba keratitis is due to greater virulence or greater prevalence of this genotype, Acanthamoeba genotypes were determined for 13 keratitis isolates and 12 environmental isolates from Iran. Among 13 clinical isolates, eight (61.5%) belonged to T4, two (15.3%) belonged to T3 and three (23%) belonged to the T2 genotype. In contrast, the majority of 12 environmental isolates tested in the present study belonged to T2 (7/12, 58.3%), followed by 4/12 T4 isolates (33.3%). In addition, the genotypes of six new Acanthamoeba isolates from UK keratitis cases were determined. Of these, five (83.3%) belonged to T4 and one was T3 (16.6%), supporting the expected high frequency of T4 in Acanthamoeba keratitis. In total, the genotypes of 24 Acanthamoeba keratitis isolates from the UK and Iran were determined. Of these, 17 belonged to T4 (70.8%), three belonged to T2 (12.5%), three belonged to T3 (12.5%) and one belonged to T11 (4.1%), confirming that T4 is the predominant genotype (S2=4.167; P=0.0412) in Acanthamoeba keratitis.

Isolation and identification of pathogenic Acanthamoeba strains in Tenerife, Canary Islands, Spain from water sources

A comprehensive survey to document the presence of free-living amoebae of the genus Acanthamoeba was conducted in tap water and sea water sources related to human environments in Tenerife, Canary Islands, Spain. Acanthamoeba identification was based on the morphology of cyst and trophozoite forms and PCR amplification with a genus-specific primer pair. The pathogenic potential of Acanthamoeba isolates was characterized by temperature and osmotolerance assays and PCR reactions with two primer pairs related to Acanthamoeba pathogenesis. The results demonstrate the presence of potentially pathogenic strains in both sources. Thus, some of the amoebae in these aquatic habitats can act as opportunistic pathogens, could play a role in the diseases of aquatic organisms, and may present a risk to human health.

Free-living amoebae as opportunistic and non-opportunistic pathogens of humans and animals

Knowledge that free-living amoebae are capable of causing human disease dates back some 50 years, prior to which time they were regarded as harmless soil organisms or, at most, commensals of mammals. First Naegleria fowleri, then Acanthamoeba spp. and Balamuthia mandrillaris, and finally Sappinia diploidea have been recognised as etiologic agents of encephalitis; Acanthamoeba spp. are also responsible for amoebic keratitis. Some of the infections are opportunistic, occurring mainly in immunocompromised hosts (Acanthamoeba and Balamuthia encephalitides), while others are non-opportunistic (Acanthamoeba keratitis, Naegleria meningoencephalitis, and cases of Balamuthia encephalitis occurring in immunocompetent humans). The amoebae have a cosmopolitan distribution in soil and water, providing multiple opportunities for contacts with humans and animals, as evidenced by antibody titers in surveyed human populations. Although, the numbers of infections caused by these amoebae are low in comparison to other protozoal parasitoses (trypanosomiasis, toxoplasmosis, malaria, etc.), the difficulty in diagnosing them, the challenge of finding optimal antimicrobial treatments and the morbidity and relatively high mortality associated with, in particular, the encephalitides have been a cause for concern for clinical and laboratory personnel and parasitologists. This review presents information about the individual amoebae: their morphologies and life-cycles, laboratory cultivation, ecology, epidemiology, nature of the infections and appropriate antimicrobial therapies, the immune response, and molecular diagnostic procedures that have been developed for identification of the amoebae in the environment and in clinical specimens.