Paradigms of Protist/Bacteria Symbioses Affecting Human Health: Acanthamoeba species and Trichomonas vaginalis

Interaction between Acanthamoeba and Staphylococcus

Free-living amoebae of the genus Acanthamoeba are infected by various bacteria in nature, and thus bacteria can protect themselves from adverse environmental conditions. Contrary to this ameba-bacteria relationship whether Acanthamoeba has antibacterial effects on bacteria is the different aspect of the relationship between these microorganisms. In this study, we investigate various Acanthamoeba strains have antibacterial effects on various Staphylococcus strains. Three environmental Acanthamoeba strains, isolated from various aquatic environments in Turkey, and Acanthamoeba castellanii ATCC 50373 standard strains were used in the study. The antistaphylococcal effect of cell-free supernatant (CFS) obtained from these amoebae against 12 different Staphylococcus bacteria was investigated by colony counting method. In addition, the pathogenicity of the tested Acanthamoeba strains was determined using osmotolerance and thermotolerance tests. CFSs obtained from Acanthamoeba were found to have varying degrees of antistaphylococcal effects on various Staphylococcus strains (0%-100%). It was determined that the CFS of the standard Acanthamoeba strain showed 100% inhibitory effect against one clinical methicillin-resistant Staphylococcus aureus strain (M2). Also, CFS of Ugöl strain showed 99.97% inhibitory effect against one clinical methicillin-sensitive Staphylococcus epidermidis strain (L3). It was determined that all Acanthamoeba isolates had no pathogenic potential. According to the results, it has been observed that Acanthamoeba produces antibacterial substance(s) against Staphylococcus bacteria and that the ameba-bacteria relationship may also result in the detriment of the bacteria. Furthermore, the current study indicates that new and natural antimicrobial agents from Acanthamoeba can be used as an alternative to infections caused by Staphylococcus.

Zooming in on the intracellular microbiome composition of bacterivorous Acanthamoeba isolates

Acanthamoeba, a free-living amoeba in water and soil, is an emerging pathogen causing severe eye infection known as Acanthamoeba keratitis. In its natural environment, Acanthamoeba performs a dual function as an environmental heterotrophic predator and host for a range of microorganisms that resist digestion. Our objective was to characterize the intracellular microorganisms of phylogenetically distinct Acanthamoeba spp. isolated in Australia and India through directly sequencing 16S rRNA amplicons from the amoebae. The presence of intracellular bacteria was further confirmed by in situ hybridization and electron microscopy. Among the 51 isolates assessed, 41% harboured intracellular bacteria which were clustered into four major phyla: Pseudomonadota (previously known as Proteobacteria), Bacteroidota (previously known as Bacteroidetes), Actinomycetota (previously known as Actinobacteria), and Bacillota (previously known as Firmicutes). The linear discriminate analysis effect size analysis identified distinct microbial abundance patterns among the sample types; Pseudomonas species was abundant in Australian corneal isolates (P < 0.007), Enterobacteriales showed higher abundance in Indian corneal isolates (P < 0.017), and Bacteroidota was abundant in Australian water isolates (P < 0.019). The bacterial beta diversity of Acanthamoeba isolates from keratitis patients in India and Australia significantly differed (P < 0.05), while alpha diversity did not vary based on the country of origin or source of isolation (P > 0.05). More diverse intracellular bacteria were identified in water isolates as compared with clinical isolates. Confocal and electron microscopy confirmed the bacterial cells undergoing binary fission within the amoebal host, indicating the presence of viable bacteria. This study sheds light on the possibility of a sympatric lifestyle within Acanthamoeba, thereby emphasizing its crucial role as a bunker and carrier of potential human pathogens.

Monitoring potentially pathogenic protists in sewage sludge using Metataxonomics

Intestinal parasites continue to pose a significant threat to human health worldwide, particularly among children. Contaminated water and soil serve as major transmission vehicles for these parasites and intestinal protists are among the most prevalent parasites in both developed and developing nations. Traditionally, parasites have been studied using human or animal fecal samples, while studying them in environmental samples has been challenging due to technical limitations. However, advancements in Next-Generation Sequencing (NGS) and bioinformatic approaches now enable the detection of parasite DNA in environmental samples. In this study, we applied a metataxonomic and phylogenetic strategy to detect and classify DNA of protists present in sewage sludge from two major cities in Colombia: Medellin and Cali. We successfully detected several human pathogenic parasites including Giardia intestinalis, Entamoeba histolytica, and Blastocystis sp., among other protists, in all sludge samples examined. We also investigated the entry and exit of parasite DNA from the San Fernando wastewater treatment plant (WWTP). We observed a higher number of parasite DNA sequences in the plant's influent wastewater, but we also detected the discharge of DNA from pathogenic parasites in both effluent waters and biosolids.

Patterns of antibiotic resistance of Mycoplasma hominis endosymbiont of Trichomonas vaginalis and the influence of bacterial intracellular location on drug susceptibility

OBJECTIVES

Mycoplasma hominis, an opportunistic pathogen of the human lower urogenital tract, can survive and replicate within the protozoan Trichomonas vaginalis, establishing an endosymbiotic relationship. The intracellular location may provide a means for the bacteria to evade the immune system and protection from antimicrobial activities. Our aim was to investigate the influence of the endosymbiotic association of M. hominis with trichomonad cells on bacterial antibiotic susceptibility.

METHODS

We evaluated antibiotic resistance patterns in a group of M. hominis isolated from T. vaginalis clinical specimens as well as in M. hominis isolated from patients without trichomoniasis. Using an experimental model system, we compared the minimum inhibitory concentration (MIC) and lethal concentration (MLC) of tetracycline on M. hominis endosymbionts of T. vaginalis and extracellular bacteria.

RESULTS

The incidence rate of M. hominis strains resistant to C14 and C15 macrolide antibiotics was higher in intracellular strains associated with T. vaginalis compared with extracellular bacteria isolated from women not affected by trichomoniasis. However, sensitivity to tetracycline and quinolones was similar in both groups. In vitro experiments demonstrated that M. hominis strains, when isolated as endosymbionts from T. vaginalis, exhibited reduced sensitivity to tetracycline when cultured extracellularly for at least eight weeks.

CONCLUSION

The intracellular localization of bacteria within trichomonad cells may affect antibiotic susceptibility.

Bacterial microbiota management in free-living amoebae (Heterolobosea lineage) isolated from water: The impact of amoebae identity, grazing conditions, and passage number

Free-living amoebae (FLA) are ubiquitous protozoa mainly found in aquatic environments. They are well-known reservoirs and vectors for the transmission of amoeba-resistant bacteria (ARB), most of which are pathogenic to humans. Yet, the natural bacterial microbiota associated with FLA remains largely unknown. Herein, we characterized the natural bacterial microbiota of different FLA species isolated from recreational waters in Guadeloupe. Monoxenic cultures of Naegleria australiensis, Naegleria sp. WTP3, Paravahlkampfia ustiana and Vahlkampfia sp. AK-2007 (Heterolobosea lineage) were cultivated under different grazing conditions, during successive passages. The whole bacterial microbiota of the waters and the amoebal cysts was characterized using 16S rRNA gene metabarcoding. The culturable subset of ARB was analyzed by mass spectrometry (MALDI-TOF MS), conventional 16S PCR, and disk diffusion method (to assess bacterial antibiotic resistance). Transmission electron microscopy was used to locate the ARB inside the amoebae. According to alpha and beta-diversity analyses, FLA bacterial microbiota were significantly different from the ones of their habitat. While Vogesella and Aquabacterium genera were detected in water, the most common ARB belonged to Pseudomonas, Bosea, and Escherichia/Shigella genera. The different FLA species showed both temporary and permanent associations with differentially bacterial taxa, suggesting host specificity. These associations depend on the number of passages and grazing conditions. Additionally, Naegleria, Vahlkampfia and Paravahlkampfia cysts were shown to naturally harbor viable bacteria of the Acinetobacter, Escherichia, Enterobacter, Pseudomonas and Microbacterium genera, all being pathogenic to humans. To our knowledge, this is the first time Paravahlkampfia and Vahlkampfia have been demonstrated as hosts of pathogenic ARB in water. Globally, the persistence of these ARB inside resistant cysts represents a potential health risk. To ensure the continued safety of recreational waters, it is crucial to (i) regularly control both the amoebae and their ARB and (ii) improve knowledge on amoebae-bacteria interactions to establish better water management protocols.

Enhancement of capsular hypermucoviscosity in Klebsiella pneumoniae by Acanthamoeba

BACKGROUND

Acanthamoeba and Klebsiella pneumoniae are both environmental commensals. Recently, clinical harm caused by hypermucoviscous K. pneumoniae has been observed. However, the interaction between these microbes and the origin of hypermucoviscous K. pneumoniae have not been reported.

METHODOLOGY/PRINCIPAL FINDINGS

Here, we report that the bacterial capsule is enlarged when co-cultured with Acanthamoeba using India ink staining, and this effect depends on the number of parasites present. This interaction results in an enhancement of capsular polysaccharide production in the subsequent generations of K. pneumoniae, even without co-culturing with Acanthamoeba. The hypermucoviscosity of the capsule was examined using the sedimentation assay and string test. We also screened other K. pneumoniae serotypes, including K1, K2, K5, and K20, for interaction with Acanthamoeba using India ink staining, and found the same interaction effect.

CONCLUSIONS/SIGNIFICANCE

These findings suggest that the interaction between Acanthamoeba and K. pneumoniae could lead to harmful consequences in public health and nosocomial disease control, particularly hypermucoviscous K. pneumoniae infections.

Lipidomics Analysis of Multilamellar Bodies Produced by Amoeba Acanthamoeba castellanii in Co-Culture with Klebsiella aerogenes

Multilamellar bodies (MLBs) are membrane-bound cytoplasmic organelles of lysosomal origin. In some protozoa, they were considered as lipid storage secretory organelles and feasible participants in cell-to-cell communication. However, for Acanthamoeba castellanii, similar vesicles were indicated only as possible transmission vectors of several pathogenic bacteria without attributing them biological roles and activities. Since amoebae belonging to the genus Acanthamoeba are not only of environmental but also of clinical significance, it is of great importance to fully understand their physiology. Thus, determination of MLB lipid composition could partly address these questions. Because MLBs are secreted by amoebae as a result of bacteria digestion, the co-culture technique with the use of “edible” Klebsiella aerogenes was used for their production. Lipids obtained from The MLB fraction, previously purified from bacterial debris, were analyzed by high-performance thin-layer chromatography, gas chromatography coupled with mass spectrometry, and high-resolution mass spectrometry. Lipidomic analysis revealed that in MLBs, a very abundant lipid class was a non-phosphorous, polar glycerolipids, diacylglyceryl-O-(N,N,N)-trimethylhomoserine (DGTS). Since DGTSs are regarded as a source of nitrogen and fatty acids, MLBs can be considered as lipid storage organelles produced in stress conditions. Further, the identification of phytoceramides and possible new betaine derivatives indicates that MLBs might have a distinct bioactive potential.

Beyond bacteria: Reconstructing microorganism connections and deciphering the predicted mutualisms in mammalian gut metagenomes

Numerous gut microbial studies have focused on bacteria. However, archaea, viruses, fungi, protists, and nematodes are also regular residents of the gut ecosystem. Little is known about the composition and potential interactions among these six kingdoms in the same samples. Here, we unraveled the complex connection among them using approximately 123 gut metagenomes from 42 mammalian species (including carnivores, omnivores, and herbivores). We observed high variation in bacterial and fungal families and relatively low variation in archaea, viruses, protists, and nematodes. We found that some fungi in the mammalian intestine might come from environmental sources (e.g., soil and dietary plants), and some might be native to the intestine (e.g., the occurrence of Neocallimastigomycetes). The Methanobacteriaceae and Plasmodiidae families (archaea and protozoa, respectively) were predominant in these metagenomes, whereas Onchocercidae and Trichuridae were the two most common nematodes, and Siphoviridae and Myoviridae the two most common virus families in these mammalian gut metagenomes. Interestingly, most of the pairwise co-occurrence patterns were significantly positive among these six kingdoms, and significantly negative networks mainly occurred between fungi and prokaryotes (both bacteria and archaea). Our study revealed some inconvenient characteristics in the mammalian gut microorganism ecosystem: (1) the community formed by members of the analyzed kingdoms reflects the life history of the host and the potential threat posed by pathogenic protists and nematodes in mammals; and (2) the networks suggest the existence of predicted mutualism among members of these six kingdoms and of the predicted competition, mainly among fungi and other kingdoms.

Exploring the nature of interaction between shiga toxin producing Escherichia coli (STEC) and free-living amoeba - Acanthamoeba sp

Free-living amoebae (FLA) are widely distributed protozoa in nature, known to cause severe eye infections and central nervous system disorders. There is growing attention to the potential role that these protozoa could act as reservoirs of pathogenic bacteria and, consequently, to the possibility that, the persistence and spread of the latter may be facilitated, by exploiting internalization into amoebae. Shiga toxin-producing strains of Escherichia coli (STEC) are zoonotic agents capable of causing serious diseases, such as hemorrhagic colitis (HC) and hemolytic uremic syndrome (HUS). Cattle represent the main natural reservoir of STEC, which are frequently found also in other domestic and wild ruminants, often without causing any evident symptoms of disease. The aspects related to the ecology of STEC strains in animal reservoirs and the environment are poorly known, including the persistence of these microorganisms within niches unfavorable to survival, such as soils or waters. In this study we investigated the interaction between STEC strains of serotype O157: H7 with different virulence gene profiles, and a genus of a wild free-living amoeba, Acanthamoeba sp. Our results confirm the ability of STEC strains to survive up to 20 days within a wild Acanthamoeba sp., in a quiescent state persisting in a non-cultivable form, until they reactivate following some stimulus of an unknown nature. Furthermore, our findings show that during their internalization, the E. coli O157 kept the set of the main virulence genes intact, preserving their pathogenetic potential. These observations suggest that the internalization in free-living amoebae may represent a means for STEC to resist in environments with non-permissive growth conditions. Moreover, by staying within the protozoa, STEC could escape their detection in the vehicles of infections and resist to the treatments used for the disinfection of the livestock environment.

Novel Antiamoebic Tyrocidine-Derived Peptide against Brain-Eating Amoebae

Acanthamoeba castellanii (A. castellanii) can cause Acanthamoeba keratitis, a sight-threatening infection, as well as a fatal brain infection termed granulomatous amoebic encephalitis, mostly in immunocompromised individuals. In contrast, Naegleria fowleri (N. fowleri) causes a deadly infection involving the central nervous system, recognized as primary amoebic encephalitis, mainly in individuals partaking in recreational water activities or those with nasal exposure to contaminated water. Worryingly, mortality rates due to these infections are more than 90%, suggesting the need to find alternative therapies. In this study, antiamoebic activity of a peptide based on the structure of the antibiotic tyrocidine was evaluated against A. castellanii and N. fowleri. The tyrocidine-derived peptide displayed significant amoebicidal efficacy against A. castellanii and N. fowleri. At 250 μg/mL, the peptide drastically reduced amoebae viability up to 13% and 21% after 2 h of incubation against N. fowleri and A. castellanii., whereas, after 24 h of incubation, the peptide showed 86% and 94% amoebicidal activity against A. castellanii and N. fowleri. Furthermore, amoebae pretreated with 100 μg/mL peptide inhibited 35% and 53% A. castellanii and N. fowleri, while, at 250 μg/mL, 84% and 94% A. castellanii and N. fowleri failed to adhere to human cells. Amoeba-mediated cell cytopathogenicity assays revealed 31% and 42% inhibition at 100 μg/mL, while at 250 μg/mL 75% and 86% A. castellanii and N. fowleri were inhibited. Assays revealed inhibition of encystation in both A. castellanii (58% and 93%) and N. fowleri (73% and 97%) at concentrations of 100 and 250 μg/mL respectively. Importantly, tyrocidine-derived peptide depicted minimal cytotoxicity to human cells and, thus, may be a potential candidate in the rational development of a treatment regimen against free-living amoebae infections. Future studies are necessary to elucidate the in vivo effects of tyrocidine-derived peptide against these and other pathogenic amoebae of importance.

A one health approach versus Acanthamoeba castellanii, a potential host for Morganella morganii

Acanthamoeba castellanii, known as the “Trojan horse of the microbial world,” is known to host a variety of microorganisms including viruses, yeasts, protists, and bacteria. Acanthamoeba can act as a vector and may aid in the transmission of various bacterial pathogens to potential hosts and are found in a variety of places, thus impacting the health of humans, animals, and the environment. These are interconnected in a system known as “one health.” With the global threat of antibiotic resistance, bacteria may avoid harsh conditions, antibiotics, and disinfectants by sheltering within Acanthamoeba. In this study, Acanthamoeba castellanii interaction with Morganella morganii, a Gram-negative bacterium was studied. Escherichia coli K1 interaction with Acanthamoeba was carried out as a control. Association, invasion, and survival assays were accomplished. Morganella morganii was found to associate, invade, and survive within Acanthamoeba castellanii. Additionally, Escherichia coli K1 was also found to associate, invade, and survive within the Acanthamoeba at a higher number in comparison to Morganella morganii. For the first time, we have shown that Morganella morganii interact, invade, and survive within Acanthamoeba castellanii, suggesting that Acanthamoeba may be a potential vector in the transmission of Morganella morganii to susceptible hosts. Taking a one health approach to tackle and develop disinfectants to target Acanthamoeba is warranted, as the amoebae may be hosting various microbes such as multiple drug-resistant bacteria and even viruses such as the novel coronavirus.

Effect of the Symbiosis with Mycoplasma hominis and Candidatus Mycoplasma Girerdii on Trichomonas vaginalis Metronidazole Susceptibility

Trichomoniasis, the most common non-viral sexually transmitted infection worldwide, is caused by the protozoon Trichomonas vaginalis. The 5- nitroimidazole drugs, of which metronidazole is the most prescribed, are the only effective drugs to treat trichomoniasis. Resistance against metronidazole is increasingly reported among T. vaginalis isolates. T. vaginalis can establish an endosymbiosis with two Mycoplasma species, Mycoplasma hominis and Candidatus Mycoplasma girerdii, whose presence has been demonstrated to influence several aspects of the protozoan pathobiology. The role of M. hominis in T. vaginalis resistance to metronidazole is controversial, while the influence of Ca. M. girerdii has never been investigated. In this work, we investigate the possible correlation between the presence of Ca. M. girerdii and/or M. hominis and the in vitro drug susceptibility in a large group of T. vaginalis isolated in Italy and in Vietnam. We also evaluated, via RNA-seq analysis, the expression of protozoan genes involved in metronidazole resistance in a set of syngenic T. vaginalis strains, differing only for the presence/absence of the two Mycoplasmas. Our results show that the presence of M. hominis significantly increases the sensitivity to metronidazole in T. vaginalis and affects gene expression. On the contrary, the symbiosis with Candidatus Mycoplasma girerdii seems to have no effect on metronidazole resistance in T. vaginalis.

Mycoplasmas as Host Pantropic and Specific Pathogens: Clinical Implications, Gene Transfer, Virulence Factors, and Future Perspectives

Mycoplasmas as economically important and pantropic pathogens can cause similar clinical diseases in different hosts by eluding host defense and establishing their niches despite their limited metabolic capacities. Besides, enormous undiscovered virulence has a fundamental role in the pathogenesis of pathogenic mycoplasmas. On the other hand, they are host-specific pathogens with some highly pathogenic members that can colonize a vast number of habitats. Reshuffling mycoplasmas genetic information and evolving rapidly is a way to avoid their host's immune system. However, currently, only a few control measures exist against some mycoplasmosis which are far from satisfaction. This review aimed to provide an updated insight into the state of mycoplasmas as pathogens by summarizing and analyzing the comprehensive progress, current challenge, and future perspectives of mycoplasmas. It covers clinical implications of mycoplasmas in humans and domestic and wild animals, virulence-related factors, the process of gene transfer and its crucial prospects, the current application and future perspectives of nanotechnology for diagnosing and curing mycoplasmosis, Mycoplasma vaccination, and protective immunity. Several questions remain unanswered and are recommended to pay close attention to. The findings would be helpful to develop new strategies for basic and applied research on mycoplasmas and facilitate the control of mycoplasmosis for humans and various species of animals.

Diagnostic Considerations for Non-Acanthamoeba Amoebic Keratitis and Clinical Outcomes

Cases of amoebic keratitis involving species other than Acanthamoeba are hypothesised to be underdiagnosed and poorly understood. Amoebic keratitis is debilitating and associated with chronic visual impairment. Understanding associated symptoms of non-Acanthamoeba amoebic keratitis could facilitate new diagnostic procedures and enable prompt treatment, ultimately leading to improved patient outcomes. Thus, a review of the literature was undertaken surrounding non-Acanthamoeba amoebic keratitis. Cases were geographically widespread and mostly confined to contact lens wearers ≤ 30 years old exposed to contaminated water sources and/or demonstrating poor lens hygiene. Vermamoeba vermiformis (previously Hartmanella vermiformis) was the most common causative agent, and a moderate number of mixed keratitis cases were also reported. A crucial disease indicator was early onset stromal deterioration/ulcerations, reported in 10 of the studies, usually only occurring in advanced Acanthamoeba keratitis. Mixed infections were the most difficult to treat, often requiring keratoplasty after unsuccessful combination treatment regimens. New diagnostic measures for non-Acanthamoeba amoebic keratitis should consider early onset stromal disease as a key disease indicator. Deep corneal scrapes are also necessary for accurate amoebic identification. Moreover, a combination approach to diagnosis is advised and should involve culture, microscopy and PCR techniques. In vitro drug sensitivity tests should also be conducted to help develop patient-specific treatment regimes.

Trichomonas vaginalis follow-up and persistence in Colombian women

Trichomonas vaginalis (TV), the most common non-viral sexually-transmitted infection is considered a neglected infection and its epidemiology is not well known. This study determined TV-infection dynamics in a retrospective cohort of Colombian women and evaluated associations between risk factors and TV-outcome. TV was identified by PCR. Cox proportional risk models were used for evaluating the relationship between TV-outcome (infection, clearance and persistence) and risk factors (sexually-transmitted infections and sociodemographic characteristics). Two hundred and sixty-four women were included in the study; 26.1% had TV at the start of the study, 40.9% suffered at least one episode of infection and 13.0% suffered more than one episode of TV during the study. Women suffering HPV had a greater risk of TV-infection (aHR 1.59), high viral-load (> 10²) for HPV-16 being related to a greater risk of persistent parasite infection; a high viral load (> 10²) for HPV-18 and -33 was related to a lower probability of TV-clearance. Ethnicity (afrodescendent/indigenous people: aHR 5.11) and having had more than two sexual partners (aHR 1.94) were related to greater risk of infection, contrasting with women having a background of abortions and lower probability of having TV (aHR 0.50). Women aged 35- to 49-years-old (aHR 2.08), increased years of sexual activity (aHR 1.10), multiple sexual partners (aHR 8.86) and multiparous women (aHR 3.85) led to a greater probability of persistence. Women whose cervical findings worsened had a 9.99 greater probability of TV-persistence. TV distribution was high in the study population; its coexistence with HPV and other risk factors influenced parasite infection dynamics. The results suggested that routine TV detection should be considered regarding populations at risk of infection.

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.

A Systematic Review of Intracellular Microorganisms within Acanthamoeba to Understand Potential Impact for Infection

Acanthamoeba, an opportunistic pathogen is known to cause an infection of the cornea, central nervous system, and skin. Acanthamoeba feeds different microorganisms, including potentially pathogenic prokaryotes; some of microbes have developed ways of surviving intracellularly and this may mean that Acanthamoeba acts as incubator of important pathogens. A systematic review of the literature was performed in order to capture a comprehensive picture of the variety of microbial species identified within Acanthamoeba following the Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) guidelines. Forty-three studies met the inclusion criteria, 26 studies (60.5%) examined environmental samples, eight (18.6%) studies examined clinical specimens, and another nine (20.9%) studies analysed both types of samples. Polymerase chain reaction (PCR) followed by gene sequencing was the most common technique used to identify the intracellular microorganisms. Important pathogenic bacteria, such as E. coli, Mycobacterium spp. and P. aeruginosa, were observed in clinical isolates of Acanthamoeba, whereas Legionella, adenovirus, mimivirus, and unidentified bacteria (Candidatus) were often identified in environmental Acanthamoeba. Increasing resistance of Acanthamoeba associated intracellular pathogens to antimicrobials is an increased risk to public health. Molecular-based future studies are needed in order to assess the microbiome residing in Acanthamoeba, as a research on the hypotheses that intracellular microbes can affect the pathogenicity of Acanthamoeba infections.