Resistance of Acanthamoeba cysts to disinfection treatments used in health care settings

Anti-Acanthamoebic effects of silver-conjugated tetrazole nanoparticle

Tetrazoles are five-membered ring aromatic heterocyclic molecules that consist of one carbon and four nitrogen atoms. Several tetrazole-based drugs have shown promising activities against bacteria, fungi, asthma, cancer, hypertension etc. The overall aim of this study was to determine anti-Acanthamoebic properties of tetrazoles and tetrazole-conjugated silver nanoparticles. Tetrazole-conjugated silver nanoparticles were synthesized and confirmed using ultraviolet-visible spectrometry, Dynamic light scattering, and Fourier-transform infrared spectroscopy. Using amoebicidal, encystment, and excystment assays, the findings revealed that tetrazoles exhibited antiamoebic properties and these effects were enhanced when conjugated with silver nanoparticles. Importantly, conjugation with silver nanoparticles inhibited parasite-mediated human cell death in vitro, as measured by lactate dehydrogenase release, but it reduced toxic effects of drugs alone on human cells. Overall, these results showed clearly that tetrazoles exhibit potent antiamoebic properties which can be enhanced by conjugation with silver nanoparticles and these potential in the rational development of therapeutic interventions against parasitic infections such as keratitis and granulomatous amoebic encephalitis due to pathogenic Acanthamoeba.

EVALUATION OF THE CYSTICIDAL ACTIVITY OF CHLOROCRESOL AGAINST ACANTHAMOEBA POLYPHAGA

Chlorocresol has antibacterial and antifungal properties, yet its effectiveness in eradicating Acanthamoeba spp. remains unexplored. Acanthamoeba species trophozoites are usually sensitive to biocides, whereas cysts tend to be more resistant. This study aimed to evaluate the cysticidal activity of chlorocresol against Acanthamoeba polyphaga. Chlorocresol concentrations of 0.02, 0.04, and 0.08% were prepared and A. polyphaga cysts were incubated at room temperature (28-37 C) for 1, 24, 48, and 72 hr at each concentration. Cyst viability was evaluated using trypan blue staining and the percentage of nonviable cysts was calculated. For qualification assays, treated cysts were cultured on nonnutrient agar medium coated with Escherichia coli, incubated at 30 C, observed under a stereomicroscope for 30 days, and inoculated into peptone-yeast extract-glucose medium at 30 C for 72 hr. The results revealed that the A. polyphaga cysts were susceptible to 0.02, 0.04, and 0.08% chlorocresol. Chlorocresol made a significant difference in viability (P < 0.001) compared with the nontreated control for the same incubation time. This is the first study to examine the efficacy of chlorocresol against A. polyphaga cysts and it was highly effective. Chlorocresol could thus serve as an alternative chemical disinfectant for the eradication of A. polyphaga cysts as well as a prophylactic against transmission of other pathogenic microorganisms for which Acanthamoeba species can act as a carrier.

Spatiotemporal distribution of thermophilic free-living amoebae in recreational waters: A 5-year survey in Guadeloupe (French West Indies)

Free-living amoebae (FLA) such as Acanthamoeba, Balamuthia mandrillaris, Naegleria fowleri and Sappinia pedata are naturally widespread in freshwater, causing rare but fatal and debilitating infections in humans. Although recent studies have shown an increase in infection rates, there is a paucity of epidemiological studies regarding the presence of these emerging pathogens in water. Herein, we studied the diversity and relative abundance of thermophilic FLA in different recreational baths in a tropical climate for 5 years. From 2018 to 2022, a total of 96 water samples were collected from 7 recreational baths (natural, tiled, regularly cleaned or not, and with temperatures ranging from 27 to 40 °C). DNA was extracted from FLA cultivated at 37 °C to detect thermophilic culturable FLA. Metabarcoding studies were conducted through FLA 18S rRNA gene amplicons sequencing; amplicon sequence variants (ASV) were extracted from each sample and taxonomy assigned against PR2 database using dada2 and phyloseq tools. We also searched for Naegleria sp. and N. fowleri using PCR targeting ITS and NFITS genes (respectively) and we quantified them using an optimized most probable number (MPN) method for FLA. Our results showed that differences in FLA diversity and abundance were observed amongst the 7 baths, but without a clear seasonal distribution. Naegleria, Vermamoeba and Stenamoeba were the most represented genera, while the genera Acanthamoeba and Vahlkampfia were mainly found in 2 baths. The MPN values for Naegleria sp. (NT/l) increased between 2018 and 2022, but the MPN values for N. fowleri (NF/l) seemed to decrease. Globally, our results showed that since we cannot establish a seasonal distribution of FLA, the regular presence of FLA (namely Naegleria and Acanthamoeba) in recreational waters can pose a potential threat in terms of neuroinfections as well as Acanthamoeba keratitis. It is thus imperious to perform the regular control of these baths as a preventive health measure.

Reliable and specific detection of Acanthamoeba spp. in dishcloths using quantitative real-time PCR assay

Acanthamoeba spp., are ubiquitous protist which belongs to Free-Living Amoeba (FLA) group, is considered as causal agent of side-threatening keratitis or fatal encephalitis among other human infections. Besides, this parasite has been reported as host for other microorganisms important to human health such as Campylobacter spp. or Vibrio spp. among others. This role of Acanthamoeba as pathogen and environmental phagocyte has increased the reports confirming its presence in human related environments, acting as a water quality indicator. Considering the tide relationship between water and kitchen environments, and the high prevalence of Acanthamoeba in water sources, the present study aims to establish a quick and accurate protocol based on DNA extraction and a real time qPCR assay to detect Acanthamoeba spp. in dishcloths. The procedure has been validated by processing 17 used dishcloths. Our findings demonstrated the high sensitivity of the qPCR assay used which was capable of detecting up to one Acanthamoeba from an in vitro contaminated dishcloth. The protocol accurately detected 64.7% of positive samples for Acanthamoeba spp, (in 4 samples DNA concentrations corresponded to 1-102 amoebae). Our findings demonstrate the importance of FLA surveillance by efficient and sensitive methods since one amoeba is capable of colonizing human related food environments such as kitchens sinks and could be a potential source of infection.

Combating the causative agent of amoebic keratitis, Acanthamoeba castellanii, using Padina pavonica alcoholic extract: toxicokinetic and molecular docking approaches

Natural products play a significant role in providing the current demand as antiparasitic agents, which offer an attractive approach for the discovery of novel drugs. The present study aimed to evaluate in vitro the potential impact of seaweed Padina pavonica (P. pavonica) extract in combating Acanthamoeba castellanii (A. castellanii). The phytochemical constituents of the extract were characterized by Gas chromatography-mass spectrometry. Six concentrations of the algal extract were used to evaluate its antiprotozoal activity at various incubation periods. Our results showed that the extract has significant inhibition against trophozoites and cysts viability, with complete inhibition at the high concentrations. The IC50 of P. pavonica extract was 4.56 and 4.89 µg/mL for trophozoites and cysts, respectively, at 24 h. Morphological alterations of A. castellanii trophozoites/cysts treated with the extract were assessed using inverted and scanning electron microscopes and showed severe damage features upon treatment with the extract at different concentrations. Molecular Docking of extracted compounds against Acanthamoeba cytochrome P450 monooxygenase (AcCYP51) was performed using Autodock vina1.5.6. A pharmacokinetic study using SwissADME was also conducted to investigate the potentiality of the identified bioactive compounds from Padina extract to be orally active drug candidates. In conclusion, this study highlights the in vitro amoebicidal activity of P. pavonica extract against A. castellanii adults and cysts and suggests potential AcCYP51 inhibition.

Occurrence of Free-Living Amoebae in Non-Human Primate Gut

The gut microbiome reflects health and predicts possible disease in hosts. A holistic view of this community is needed, focusing on identifying species and dissecting how species interact with their host and each other, regardless of whether their presence is beneficial, inconsequential, or detrimental. The distribution of gut-associated eukaryotes within and across non-human primates is likely driven by host behavior and ecology. To ascertain the existence of free-living amoebae (FLA) in the gut of wild and captive non-human primates, 101 stool samples were collected and submitted to culture-dependent microscopy examination and DNA sequencing. Free-living amoebae were detected in 45.4% (46/101) of fecal samples analyzed, and their morphological characteristics matched those of Acanthamoeba spp., Vermamoeba spp., heterolobosean amoeboflagellates and fan-shaped amoebae of the family Vannellidae. Sequence analysis of the PCR products revealed that the suspected amoebae are highly homologous (99% identity and 100% query coverage) with Acanthamoeba T4 genotype and Vermamoeba vermiformis amoebae. The results showed a great diversity of amoebae in the non-human primate's microbiome, which may pose a potential risk to the health of NHPs. To our knowledge, this is the first report of free-living amoebae in non-human primates that are naturally infected. However, it is unknown whether gut-borne amoebae exploit a viable ecological niche or are simply transient residents in the gut.

First report of Acanthamoebae spp. isolation from a volcanic mud spring in the Philippines

Acanthamoebae spp. is considered highly adaptive. The present study aims to establish the occurrence of free-living amoebae, particularly Acanthamoebae, to exist in extreme environments such as volcanic mud springs. Fifty surface water samples were collected from mud springs (34 samples), and flat rocks (16 samples) were collected, processed, and cultured. After 14 days of incubation, 32 (64%) plates showed positive amoebic growth. Nineteen (55.8%) of these plates came from the mud spring collection site, while 13 (81.2%) samples are from flat rock sources. DNAs from positive samples were made to react to polymerase chain reaction (PCR) using primer sets JDP1 5'GGCCCAGATCGTTTACCGTGAA-3' and JDP2 5'TCTCACAAGCTGCTAGGGAGTCA-3' for cells that resemble Acanthamoebae. Sequencing and basic local alignment search tool (BLAST) revealed a 99% similarity of isolates to Acanthamoebae spp. Identification of Acanthamoebae spp that can survive in higher temperatures is important public health information. The existence of such isolates in the environment has dire health implications, which suggests revisitation of water treatment protocols. Detection of such organisms in environmental sources used for recreational purposes provides information to local and international tourists who frequent them. This will result in the mitigation of potential future infection.

Protozoan-Priming and Magnesium Conditioning Enhance Legionella pneumophila Dissemination and Monochloramine Resistance

Opportunistic pathogens (OPs) are of concern in drinking water distribution systems because they persist despite disinfectant residuals. While many OPs garner protection from disinfectants via a biofilm lifestyle, Legionella pneumophila (Lp) also gains disinfection resistance by being harbored within free-living amoebae (FLA). It has been long established, but poorly understood, that Lp grown within FLA show increased infectivity toward subsequent FLA or human cells (i.e., macrophage), via a process we previously coined "protozoan-priming". The objectives of this study are (i) to identify in Lp a key genetic determinant of how protozoan-priming increases its infectivity, (ii) to determine the chemical stimulus within FLA to which Lp responds during protozoan-priming, and (iii) to determine if more infectious forms of Lp also exhibit enhanced disinfectant resistance. Using Acanthamoeba castellanii as a FLA host, the priming effect was isolated to Lp's sidGV locus, which is activated upon sensing elevated magnesium concentrations. Supplementing growth medium with 8 mM magnesium is sufficient to produce Lp grown in vitro with an infectivity equivalent to that of Lp grown via the protozoan-primed route. Both Lp forms with increased infectivity (FLA-grown and Mg2+-supplemented) exhibit greater monochloramine resistance than Lp grown in standard media, indicating that passage through FLA not only increases Lp's infectivity but also enhances its monochloramine resistance. Therefore, laboratory-based testing of disinfection strategies should employ conditions that simulate or replicate intracellular growth to accurately assess disinfectant resistance.

Effects of In Vitro Combination of Nitric Oxide Donors and Hypochlorite on Acanthamoeba castellanii Viability

Purpose

To investigate the combined anti-Acanthamoeba effects of nitric oxide (NO) donors and hypochlorite to maximize amoebicidal outcomes while minimizing damage to human corneal epithelial cells (HCECs).

Methods

Acanthamoeba castellanii and primary cultured HCECs and keratocytes were treated with sodium hypochlorite (NaOCl), NO donors (sodium nitroprusside [SNP] and sodium nitrite [NaNO2]), or a combination of hypochlorite and NO donors. The viability of A. castellanii, HCECs, and keratocytes was assessed. Minimal inhibitory concentration (MIC) and fractional inhibitory concentration of NaOCl and NO donors were determined. The activation of mammalian targets of rapamycin (mTOR) and ERK and the expression of nitrite reductase and Nrf2 were assessed in HCECs using Western blot analysis. The cysticidal effects of combined NaOCl and NO donors were also evaluated.

Results

A dose-dependent toxicity was observed in A. castellanii, HCECs, and keratocytes when treated with NaOCl and SNP. The range of tested NaNO2 concentrations showed no significant toxicity to HCECs; however, dose-dependent toxicity to A. castellanii was observed. The MIC of NaOCl against HCECs and A. castellanii was 8.0 mg/mL. The MIC of NaNO2 and SNP was 500 mM and 10 mM in both HCECs and A. castellanii, respectively. Weak attenuation of the mTOR and ERK phosphorylation was observed and Nrf2 expression decreased slightly after exposure of HCECs to 2.0 mg/mL NaOCl. For the combination treatment, NaOCl (0.125 mg/mL) was selected based on the safety of HCECs and the toxicity of A. castellanii. A more potent anti-Acanthamoeba effect and HCEC toxicity were observed when NaOCl was combined with SNP rather than NaNO2.

Conclusions

Combined NaOCl and NO donors had a stronger anti-Acanthamoeba effect compared to either drug alone.

Translational Relevance

This study demonstrates that the combined use of various drugs for the treatment of Acanthamoeba infection can enhance the anti-Acanthamoeba effect while minimizing the toxicity of the individual drug.

Interactions between free-living amoebae and Cryptosporidium parvum: an experimental study

Free-Living Amebae (FLA) and Cryptosporidium oocysts occasionally share the same environment. From 2004 to 2016, Cryptosporidium was responsible for 60% of 905 worldwide waterborne outbreaks caused by protozoan parasites. The aim of this study was to evaluate interactions between C. parvum oocysts and two common FLAs (Acanthamoeba castellanii and Vermamoeba vermiformis) in a water environment. Encystment and survival of FLAs were evaluated by microscopy using trypan blue vital coloration. Oocysts were numerated on microscopy. Interactions were studied over time in conditions both unfavorable and favorable to phagocytosis. Potential phagocytosis was directly evaluated by several microscopic approaches and indirectly by numeration of microorganisms and oocyst infectivity evaluation. Occasional phagocytosis of C. parvum by FLAs was documented. However, oocyst concentrations did not decrease significantly, suggesting resistance of oocysts to phagocytosis. A temporary decrease of oocyst infectivity was observed in the presence of A. castellanii. The effect of these interactions on C. parvum infectivity is particularly interesting. The biofilm condition could favor the persistence or even the proliferation of oocysts over time. This study demonstrated interactions between C. parvum and FLAs. Further knowledge of the mechanisms involved in the decrease of oocyst infectivity in the presence of A. castellanii could facilitate the development of new therapeutic approaches.

Identifying the function of genes involved in excreted vesicle formation in Acanthamoeba castellanii containing Legionella pneumophila

BACKGROUND

Legionella spp. can survive and replicate inside host cells such as protozoa and macrophages. After enough growth, Legionella is released from the host cells as free legionellae or Legionella-filled vesicles. The vesicles support Legionella to survive for a long time in the environment and transmit to a new host. In this study, we identified the differentially expressed genes of Acanthamoeba infected by Legionella (ACA1_114460, ACA1_091500, and ACA1_362260) and examined their roles in the formation of the excreted vesicles and escape of Legionella from the Acanthamoeba.

METHODS

After ingestion of Escherichia coli and Legionella pneumophila, expression levels of target genes in Acanthamoeba were measured by real-time polymerase chain reaction (PCR) analysis. The roles of target genes were investigated by transfection of small interfering RNA (siRNA). The formation of Legionella-containing excreted vesicles and the vesicular co-localization with the lysosomes were examined by Giemsa stain and LysoTracker stain.

RESULTS

ACA1_114460, ACA1_091500, and ACA1_362260 were upregulated after ingestion of Legionella in Acanthamoeba. ACA1_114460- and ACA1_091500-silenced Acanthamoeba failed to form the Legionella-containing excreted vesicles. Legionella was released as free legionellae from the Acanthamoeba. When the ACA1_362260 of Acanthamoeba was silenced, Legionella-containing excreted vesicles were fused with the lysosome.

CONCLUSIONS

These results indicated that ACA1_114460, ACA1_091500, and ACA1_362260 of Acanthamoeba played important roles in the formation of Legionella-containing excreted vesicles and inhibition of the lysosomal co-localization with the phagosome.

Acanthamoeba spp. aggregate and encyst on contact lens material increasing resistance to disinfection

Introduction

Acanthamoeba keratitis is often caused when Acanthamoeba contaminate contact lenses and infect the cornea. Acanthamoeba is pervasive in the environment as a motile, foraging trophozoite or biocide-resistant and persistent cyst. As contact lens contamination is a potential first step in infection, we studied Acanthamoeba's behavior and interactions on different contact lens materials. We hypothesized that contact lenses may induce aggregation, which is a precursor to encystment, and that aggregated encystment would be more difficult to disinfect than motile trophozoites.

Methods

Six clinically and/or scientifically relevant strains of Acanthamoeba (ATCC 30010, ATCC 30461, ATCC 50370, ATCC 50702, ATCC 50703, and ATCC PRA-115) were investigated on seven different common silicone hydrogel contact lenses, and a no-lens control, for aggregation and encystment for 72 h. Cell count and size were used to determine aggregation, and fluorescent staining was used to understand encystment. RNA seq was performed to describe the genome of Acanthamoeba which was individually motile or aggregated on different lens materials. Disinfection efficacy using three common multi-purpose solutions was calculated to describe the potential disinfection resistance of trophozoites, individual cysts, or spheroids.

Results

Acanthamoeba trophozoites of all strains examined demonstrated significantly more aggregation on specific contact lens materials than others, or the no-lens control. Fluorescent staining demonstrated encystment in as little as 4 hours on contact lens materials, which is substantially faster than previously reported in natural or laboratory settings. Gene expression profiles corroborated encystment, with significantly differentially expressed pathways involving actin arrangement and membrane complexes. High disinfection resistance of cysts and spheroids with multi-purpose solutions was observed.

Discussion

Aggregation/encystment is a protective mechanism which may enable Acanthamoeba to be more disinfection resistant than individual trophozoites. This study demonstrates that some contact lens materials promote Acanthamoeba aggregation and encystment, and Acanthamoeba spheroids obstruct multi-purpose solutions from disinfecting Acanthamoeba.

Free-living amoebae in an oil refinery wastewater treatment facility

Free Living Amoebae (FLA) are ubiquitous microorganisms reported from harsh environmental conditions. Oil refinery facilities consume vast volumes of water during their processes, generating a large amount of wastewater. The present study aimed to evaluate the wastewater treatment process in an oil refinery wastewater treatment facility (ORWWTF) for the presence of FLA. Water samples were collected from an oil refinery wastewater (ORWW) for nine months. After recording physical-chemical features, samples were cultivated onto non-nutrient agar (NNA). The discriminative fragments of the ribosomal RNA (rRNA) gene were amplified and sequenced to characterize the isolated FLA. Phylogenetic tree, and network analysis were employed to evaluate genetic relationships. The thermo- and osmotolerant tests were performed on the isolated FLA. Twenty-five (32.9%) samples were positive for FLA cultivation. Acanthamoeba spp., Vahlkampfiids, and Vermamoeba spp. were detected, of which Acanthamoeba species were predominant. There was no statistical correlation between pH, NH₃, PO₄, H₂S, and TDS with the presence of FLA. A statistical correlation between the presence of FLA and the type of wastewater treatment plants (WWTPs) was significant (P-value = 0.011). All Acanthamoeba spp. isolates belonged to the genotypes T4 (17/21; 80.95%) and T11 (4/21; 19.05%). Vahlkampfiids were Naegleria spp., (7/10; 70%), Tetramitus aberdonicus (1/10; 10%), Learamoeba spp., (1/10; 10%), and Vahlkampfia spp., (1/10; 10%). All three Vermamoeba spp. were V. vermiformis. The ORWW contains toxic materials, and a few microorganisms can stay active in these environments. This is the first study which isolates FLA from such super harsh conditions. For the first time, T. aberdonicus, and Learamoeba spp., were isolated from oily wastewater. Our findings signify the concern due to the distribution of potentially pathogenic FLA to downstream lands via treated wastewater that may be released after treatment processing.

The Fate of Bacteria of the Bacillus cereus Group in the Amoeba Environment

The Bacillus cereus sensu lato group consists of several closely related species, including B. anthracis, B. cereus sensu stricto, and B. thuringiensis. Spores of these pathogenic bacteria are commonly found in the soil but evidence suggests that they are unable to grow in such a natural environment in the absence of nutrient input. Amoebas have been reported to be an amplifier for several species of pathogenic bacteria and their potential involvement to explain the large amount of B. thuringiensis and B. cereus spores in soil has been frequently proposed. Here, we studied the fate of Bacillus and amoebas when cultured together. We show that the virulence factors produced by B. thuringiensis and B. cereus do not affect the amoeba Acanthamoeba castellanii, which, on the contrary, can phagocytose and effectively digest vegetative Bacillus cells to grow and prevent the formation of cysts. Bacterial spores can germinate in the amoeba environment and the vegetative cells can then form chains or aggregates that appear to be less efficiently phagocyted by the amoeba. The use of transcriptional fusions between fluorescent reporter genes and stationary phase- and sporulation-specific promoters showed that the sporulation process occurs more efficiently in the presence of amoebas than in their absence. Moreover, our results showed the amoeba environment to promote spore germination and allow the bacteria to complete their developmental cycle. Overall, this study suggests that the amoeba-Bacillus interaction creates a virtuous circle in which each protagonist helps the other to develop.

Isolation and identification of potentially pathogenic free-living amoeba in drinking, surface, and stagnant water sources from Alborz Province, Iran

Free-living amoebas (FLAs) can cause neurological and ocular complications in humans. Water supplies play a critical role in transmitting FLAs to humans. The aim of the present study was to investigate the presence of FLAs in various aquatic sources including drinking water, stagnant water, and surface water in Alborz province, northern Iran, using morphological and molecular techniques. A total of 70 water samples were collected from 34 drinking waters, 23 surface waters, and 13 stagnant waters. Filtration and cultivation were employed to isolate FLAs. PCR assay was applied by using the genus-specific primers on positive samples. Pathogenicity tests (osmo- and thermo-tolerance properties) were performed for Acanthamoeba spp., positive sample. Considering the morphological criteria, four positive samples of Acanthamoeba sp., three Vermamoeba sp., two mixed Vermamoeba sp. with Vahlkamfiids, and one mixed Acanthamoeba sp. with Vahlkamfiids were isolated. Five Acanthamoeba sp. isolates were amplified using the JDP primer pairs. Among them, two genotypes, T4 (three isolates) and T5 (two isolates) corresponding to A. lenticulata, were identified. Four V. vermiformis samples were confirmed using the sequencing. This study highlighted the occurrence of potentially pathogenic waterborne FLAs in water habitats associated with high human activity. The results of such research on the prevalence of FLAs, as a human hazard, should be communicated to health policymakers.

Surgical management of acanthamoeba chorioretinitis

Purpose

Acanthamoeba chorioretinitis is a rare manifestation of the parasitic infection, and reported cases often result in enucleation. Surgical removal of Acanthamoeba chorioretinitis has not been previously described. We report a surgical case of Acanthamoeba chorioretinitis spread from keratitis that ultimately resulted in a disease-free outcome.

Observations

A healthy 80-year-old male with a history of keratoconus requiring a penetrating keratoplasty in the fellow eye presented with a severe corneal ulcer clinically consistent with Acanthamoeba keratitis. He ultimately required a penetrating keratoplasty and improved clinically until he developed vitritis on post-operative month 1 and was diagnosed with endophthalmitis. B-scan ultrasound demonstrated vitreous opacities and a large retinal mass that reduced in size following serial intravitreal injections of antibiotics, oral antibiotics, and a limited pars plana vitrectomy. He underwent a repeat pars plana vitrectomy 6 weeks later and a retinal mass in the mid-periphery with an associated tractional retinal detachment was noted. A localized retinectomy was performed around the lesion which was excised entirely, and silicone oil was instilled. Pathology of the lesion showed acute and chronic granulomatous necrotizing inflammation with the presence of several definitive amoebic organisms and numerous cells suspicious for amoebae. The patient was maintained on oral antibiotics by the Infectious Disease Service and was disease-free 1-year post-infection.

Conclusions and importance

Acanthamoeba chorioretinitis is a rare, devastating disease and often leads to enucleation. We present a surgical case showing control of the infection utilizing a surgical retinectomy. Aggressive local therapy and a multidisciplinary approach with the Infectious Disease Service may lead to a successful outcome.

Sirtinol Supresses Trophozoites Proliferation and Encystation of Acanthamoeba via Inhibition of Sirtuin Family Protein

The encystation of Acanthamoeba leads to the development of metabolically inactive and dormant cysts from vegetative trophozoites under unfavorable conditions. These cysts are highly resistant to anti-Acanthamoeba drugs and biocides. Therefore, the inhibition of encystation would be more effective in treating Acanthamoeba infection. In our previous study, a sirtuin family protein—Acanthamoeba silent-information regulator 2-like protein (AcSir2)—was identified, and its expression was discovered to be critical for Acanthamoeba castellanii proliferation and encystation. In this study, to develop Acanthamoeba sirtuin inhibitors, we examine the effects of sirtinol, a sirtuin inhibitor, on trophozoite growth and encystation. Sirtinol inhibited A. castellanii trophozoites proliferation (IC50=61.24 μM). The encystation rate of cells treated with sirtinol significantly decreased to 39.8% (200 μM sirtinol) after 24 hr of incubation compared to controls. In AcSir2-overexpressing cells, the transcriptional level of cyst-specific cysteine protease (CSCP), an Acanthamoeba cysteine protease involved in the encysting process, was 11.6- and 88.6-fold higher at 48 and 72 hr after induction of encystation compared to control. However, sirtinol suppresses CSCP transcription, resulting that the undegraded organelles and large molecules remained in sirtinol-treated cells during encystation. These results indicated that sirtinol sufficiently inhibited trophozoite proliferation and encystation, and can be used to treat Acanthamoeba infections.

Compromised Effectiveness of Thermal Inactivation of Legionella pneumophila in Water Heater Sediments and Water, and Influence of the Presence of Vermamoeba vermiformis

Intermittent reduction of temperature set-points and periodic shutdowns of water heaters have been proposed to reduce energy consumption in buildings. However, the consequences of such measures on the occurrence and proliferation of Legionella pneumophila (Lp) in hot water systems have not been documented. The impact of single and repeated heat shocks was investigated using an environmental strain of L. pneumophila and a reference strain of V. vermiformis. Heat shocks at temperatures ranging from 50 °C to 70 °C were applied for 1 h and 4 h in water and water heaters loose deposits (sludge). The regrowth potential of heat-treated culturable L. pneumophila in presence of V. vermiformis in water heaters sludges was evaluated. A 2.5-log loss of culturability of L. pneumophila was observed in simulated drinking water at 60 °C while a 4-log reduction was reached in water heaters loose deposits. Persistence of Lp after 4 h at 55 °C was shown and the presence of V. vermiformis in water heater’s loose deposits resulted in a drastic amplification (5-log). Results show that thermal inactivation by heat shock is only efficient at elevated temperatures (50 °C) in both water and loose deposits. The few remaining organisms can rapidly proliferate during storage at lower temperature in the presence of hosts.

Acanthamoeba Keratitis: an update on amebicidal and cysticidal drug screening methodologies and potential treatment with azole drugs

Introduction: Acanthamoeba encompasses several species of free-living ameba encountered commonly throughout the environment. Unfortunately, these species of ameba can cause opportunistic infections that result in Acanthamoeba keratitis, granulomatous amebic encephalitis, and occasionally systemic infection.Areas covered: This review discusses relevant literature found through PubMed and Google scholar published as of January 2021. The review summarizes current common Acanthamoeba keratitis treatments, drug discovery methodologies available for screening potential anti-Acanthamoeba compounds, and the anti-Acanthamoeba activity of various azole antifungal agents.Expert opinion: While several biguanide and diamidine antimicrobial agents are available to clinicians to effectively treat Acanthamoeba keratitis, no singular treatment can effectively treat every Acanthamoeba keratitis case.Efforts to identify new anti-Acanthamoeba agents include trophozoite cell viability assays, which are amenable to high-throughput screening. Cysticidal assays remain largely manual and would benefit from further automation development. Additionally, the existing literature on the effectiveness of various azole antifungal agents for treating Acanthamoeba keratitis is incomplete or contradictory, suggesting the need for a systematic review of all azoles against different pathogenic Acanthamoeba strains.

Inactivation of Acanthamoeba Cysts in Suspension and on Contaminated Contact Lenses Using Non-Thermal Plasma

Water suspensions of cysts of a pathogenic clinical isolate of Acanthamoeba sp. were prepared, and the cysts were inactivated either in suspension or placed on the surface of contact lenses by the non-thermal plasma produced by the DC corona transient spark discharge. The efficacy of this treatment was determined by cultivation and the presence of vegetative trophozoites indicating non-inactivated cysts. The negative discharge appeared to be more effective than the positive one. The complete inactivation occurred in water suspension after 40 min and on contaminated lenses after 50 min of plasma exposure. The properties of lenses seem to not be affected by plasma exposure; that is, their optical power, diameter, curvature, water content and infrared and Raman spectra remain unchanged.

Aspergillus niger trehalase enzyme induced morphological and protein alterations on Acanthamoeba cyst and molecular docking studies

The cytotoxicity of Acanthamoeba is yet to fully illustrate due to recalcitrant of Acanthamoeba during cyst stage. The formation of the trehalose layer at the cyst stage protects the inner components of this opportunist protozoan parasite. Trehalase from the Aspergillus niger (AnTre) activity on the cyst of Acanthamoeba was determined based on AnTre dose-response, morphological and protein changes. The interaction of the AnTre and trehalose was also visualized through docking simulation. Vacuolation of the cyst can be seen when observed under light microscopy. Membrane integrity assessment suggested possible hydrolization of the AnTre enzyme to trehalose membranes which based on acridine orange and propidium iodide staining. Surface morphology based on scanning electron microscopy revealed the formation of bulging structure that was also proved through cross sectioning observed by transmission electron microscopy. Loss of internal structure of the cysts was clearly observed. Other morphological distinction where loss of rigid shape due to the destruction of the endo- and ecto cyst layers. However, the protein profile exhibits change of trehalose layer as responses to AnTre treatment. The observed biological results were also supported by interaction simulation based on molecular docking between trehalose and AnTre enzyme. In conclusion, this enzymatic approach could be developed into selective and effective mechanism to control Acanthamoeba without affecting the host especially mammals due to the absence of trehalose elements in the tissues of mammals.

Diseases Caused by Amoebae in Fish: An Overview

Parasitic and amphizoic amoebae are ubiquitous and can affect a huge variety of hosts, from invertebrates to humans, and fish are not an exception. Most of the relationships between amoebae and fish are based on four different types: ectocommensals, ectoparasites, endocommensals and endoparasites, although the lines between them are not always clear. As ectocommensals, they are located specially on the gills and particularly the amphizoic Neoparamoeba perurans is the most relevant species, being a real pathogenic parasite in farmed salmon. It causes amoebic gill disease, which causes a progressive hyperplasia of epithelial cells in the gill filaments and lamellae. Nodular gill disease is its analogue in freshwater fish but the causative agent is still not clear, although several amoebae have been identified associated to the lesions. Other species have been described in different fish species, affecting not only gills but also other organs, even internal ones. In some cases, species of the genera Naegleria or Acanthamoeba, which also contain pathogenic species affecting humans, are usually described affecting freshwater fish species. As endocommensals, Entamoebae species have been described in the digestive tract of freshwater and marine fish species, but Endolimax nana can reach other organs and cause systemic infections in farmed Solea senegalensis. Other systemic infections caused by amoebae are usually described in wild fish, although in most cases these are isolated cases without clinical signs or significance.

Variables Affecting the Recovery of Acanthamoeba Trophozoites

While the results of Acanthamoeba testing have been extensively published, laboratories conducting such testing are left to develop their own methods in the absence of a standardized methodology. The wide disparity of methods has resulted in equally inconsistent reported results for contact lens care (CLC) products. This study's objective was to determine the source of these discrepancies by evaluating basic Acanthamoeba biology and their impact on antimicrobial efficacy testing, including the ability of a recovery method to stimulate a single trophozoite to proliferate. Antimicrobial efficacy testing was conducted using well-published Acanthamoeba strains, storage conditions, and growth-based recovery methods. To identify variables that influence results, test solutions with low Acanthamoeba disinfection rates were utilized to prevent differences from being masked by high log reductions. In addition, single-cell proliferation assays were executed to understand the growth requirements to stimulate trophozoite propagation in two recovery methods. These studies indicated that both nutrient density (>106 CFU) and the length of plate incubation (at least 14 days) could significantly influence the accurate recovery of trophozoites. Together, this study emphasizes the need to understand how Acanthamoeba trophozoites biology can impact test methods to create divergent results.

Curcuma longa rhizome extract and Curcumin reduce the adhesion of Acanthamoeba triangularis trophozoites and cysts in polystyrene plastic surface and contact lens

Curcuma longa and Curcumin have been documented to have a wide spectrum of pharmacological effects, including anti-Acanthamoeba activity. Hence, this study sought to explore the anti-adhesion activity of C. longa extract and Curcumin against Acanthamoeba triangularis trophozoites and cysts in plastic and contact lenses. Our results showed that C. longa extract and Curcumin significantly inhibited the adhesion of A. triangularis trophozoites and cysts to the plastic surface, as investigated by the crystal violet assay (P < 0.05). Also, an 80-90% decrease in adhesion of trophozoites and cysts to the plastic surface was detected following the treatment with C. longa extract and Curcumin at 1/2 × MIC, compared to the control. In the contact lens model, approximately 1 log cells/mL of the trophozoites and cysts was reduced when the cells were treated with Curcumin, when compared to the control. Pre-treatment of the plastic surface with Curcumin at 1/2-MIC reduced 60% and 90% of the adhesion of trophozoites and cysts, respectively. The reduction in 1 Log cells/mL of the adhesion of A. triangularis trophozoites was observed when lenses were pre-treated with both the extract and Curcumin. Base on the results obtained from this study, A. triangularis trophozoites treated with C. longa extract and Curcumin have lost strong acanthopodia, thorn-like projection pseudopodia observed by scanning electron microscope. This study also revealed the therapeutic potentials of C. longa extract and Curcumin, as such, have promising anti-adhesive potential that can be used in the management/prevention of A. triangularis adhesion to contact lenses.

Application of Histone Deacetylase Inhibitors MPK472 and KSK64 as a Potential Treatment Option for Acanthamoeba Keratitis

Treatment of Acanthamoeba keratitis (AK) is difficult because Acanthamoeba cysts are resistant to drugs, and as such, successful treatment requires an effective approach that inhibits cyst formation. Histone deacetylase inhibitors (HDACis) are involved in cell proliferation, differentiation, and apoptotic cell death. In this study, the effects of HDACis such as MPK472 and KSK64 on Acanthamoeba castellanii trophozoites and cysts were observed. MPK472 and KSK64 showed at least 60% amoebicidal activity against Acanthamoeba trophozoites at a concentration of 10 μM upon 8 h of treatment. Neither of the two HDACis affected mature cysts, but significant amoebicidal activities (36.4 and 33.9%) were observed against encysting Acanthamoeba following treatment with 5 and 10 μM HDACis for 24 h. Light microscopy and transmission electron microscopy results confirmed that the encystation of Acanthamoeba was inhibited by the two HDACis. In addition to this, low cytopathic effects on human corneal epithelial (HCE) cells were observed following treatment with MPK472 and KSK64 for 24 h. Our results indicate that the HDACis MPK472 and KSK64 could be used as new candidates for the development of an optimal therapeutic option for AK.

Acanthamoeba castellanii interferes with adequate chlorine disinfection of multidrug-resistant Pseudomonas aeruginosa

Verona-Integron-encoded-Metallo-β-lactamase-positive Pseudomonas aeruginosa (VIM-PA) is a cause of hard-to-treat nosocomial infections, and can colonize hospital water networks alongside Acanthamoeba. We developed an in-vitro disinfection model to examine whether Acanthamoeba castellanii can harbour VIM-PA intracellularly, allowing VIM-PA to evade being killed by currently used hospital disinfectants. We observed that A. castellanii presence resulted in significantly increased survival of VIM-PA after exposure to chlorine for 30 s or for 2 min. This undesirable effect was not observed after disinfection by 70% alcohol or 24% acetic acid. Confocal microscopy confirmed the presence of VIM-PA within A. castellanii pseudocysts. Our data indicate that A. castellanii contributes to persistent VIM-PA colonization of water systems after chlorine treatment.

Legionella pneumophila Infection Rewires the Acanthamoeba castellanii Transcriptome, Highlighting a Class of Sirtuin Genes

Legionella pneumophila is an environmental bacterium that has evolved to survive predation by soil and water amoebae such as Acanthamoeba castellanii, and this has inadvertently led to the ability of L. pneumophila to survive and replicate in human cells. L. pneumophila causes Legionnaire's Disease, with human exposure occurring via the inhalation of water aerosols containing both amoebae and the bacteria. These aerosols originate from aquatic biofilms found in artifical water sources, such as air-conditioning cooling towers and humidifiers. In these man-made environments, A. castellanii supports L. pneumophila intracellular replication, thereby promoting persistence and dissemination of the bacteria and providing protection from external stress. Despite this close evolutionary relationship, very little is known about how A. castellanii responds to L. pneumophila infection. In this study, we examined the global transcriptional response of A. castellanii to L. pneumophila infection. We compared A. castellanii infected with wild type L. pneumophila to A. castellanii infected with an isogenic ΔdotA mutant strain, which is unable to replicate intracellularly. We showed that A. castellanii underwent clear morphological and transcriptional rewiring over the course of L. pneumophila infection. Through improved annotation of the A. castellanii genome, we determined that these transcriptional changes primarily involved biological processes utilizing small GTPases, including cellular transport, signaling, metabolism and replication. In addition, a number of sirtuin-encoding genes in A. castellanii were found to be conserved and upregulated during L. pneumophila infection. Silencing of sirtuin gene, sir6f (ACA1_153540) resulted in the inhibition of A. castellanii cell proliferation during infection and reduced L. pneumophila replication. Overall our findings identified several biological pathways in amoebae that may support L. pneumophila replication and A. castellanii proliferation in environmental conditions.

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.

Presence of Acanthamoeba and diversified bacterial flora in poorly maintained contact lens cases

Acanthamoeba can cause visually destructive Acanthamoeba keratitis (AK) in contact lens (CL) users. The purpose of this study was to determine whether Acanthamoeba was present in the CL cases of CL wearers and to develop techniques to prevent the contaminations. To accomplish this, 512 CL case samples were collected from 305 healthy CL wearers. Using real-time PCR, Acanthamoeba DNA was detected in 19.1% of CL cases, however their presence was not directly associated with poor CL case care. Instead, the presence of Acanthamoeba DNA was associated with significant levels of many different bacterial species. When the CL cases underwent metagenomic analysis, the most abundant bacterial orders were Enterobacteriales followed by Burkholderiales, Pseudomonadales, and Flavobacteriales. The presence of Acanthamoeba was characterized by Propionibacterium acnes and Rothia aeria and was also associated with an increase in the α diversity. Collectively, Acanthamoeba contamination occurs when a diversified bacterial flora is present in CL cases. This can effectively be prevented by careful and thorough CL case care.

The role of the Acanthamoeba castellanii Sir2-like protein in the growth and encystation of Acanthamoeba

BACKGROUND

The encystation of Acanthamoeba leads to the development of resilient cysts from vegetative trophozoites. This process is essential for the survival of parasites under unfavorable conditions. Previous studies have reported that, during the encystation of A. castellanii, the expression levels of encystation-related factors are upregulated. However, the regulatory mechanisms for their expression during the encystation process remains unknown. Proteins in the sirtuin family, which consists of nicotinamide adenine dinucleotide-dependent deacetylases, are known to play an important role in various cellular functions. In the present study, we identified the Acanthamoeba silent-information regulator 2-like protein (AcSir2) and examined its role in the growth and encystation of Acanthamoeba.

METHODS

We obtained the full-length sequence for AcSir2 using reverse-transcription polymerase chain reaction. In Acanthamoeba transfectants that constitutively overexpress AcSir2 protein, SIRT deacetylase activity was measured, and the intracellular localization of AcSir2 and the effects on the growth and encystation of trophozoites were examined. In addition, the sirtuin inhibitor salermide was used to determine whether these effects were caused by AcSir2 overexpression RESULTS: AcSir2 was classified as a class-IV sirtuin. AcSir2 exhibited functional SIRT deacetylase activity, localized mainly in the nucleus, and its transcription was upregulated during encystation. In trophozoites, AcSir2 overexpression led to greater cell growth, and this growth was inhibited by treatment with salermide, a sirtuin inhibitor. When AcSir2 was overexpressed in the cysts, the encystation rate was significantly higher; this was also reversed with salermide treatment. In AcSir2-overexpressing encysting cells, the transcription of cellulose synthase was highly upregulated compared with that of control cells, and this upregulation was abolished with salermide treatment. Transmission electron microscope-based ultrastructural analysis of salermide-treated encysting cells showed that the structure of the exocyst wall and intercyst space was impaired and that the endocyst wall had not formed.

CONCLUSIONS

These results indicate that AcSir2 is a SIRT deacetylase that plays an essential role as a regulator of a variety of cellular processes and that the regulation of AcSir2 expression is important for the growth and encystation of A. castellanii.

In Vitro Amoebicidal Activity of Imidazolium Salts Against Trophozoites

INTRODUCTION

Several strains of the free-living genus Acanthamoeba can cause granulomatous amoebic encephalitis (GAE), a rare chronic and slowly progressive infection of the central nervous system (CNS), and Acanthamoeba keratitis (AK), a sight-threatening eye infectious disease. AK incidence has increased with the popularization of the contact lens wear and its treatment is currently limited and frequently unsuccessful. As imidazolium salts (IS), cationic imidazole derivatives, have promising antimicrobial potential.

MATERIALS AND METHODS

The present study evaluated the amoebicidal activity of four IS; 1-n-hexadecyl-3-methylimidazolium methanesulfonate (C₁₆MImMeS), chloride (C₁₆MImCl) and bis (triluoromethylsulfonyl) imide (C₁₆MImNTf2 ), and 1-methyl-3-n-octadecylimidazolium chloride (C₁₈MImCl), against the Acanthamoeba castellanii (ATCC30010) environmental strain and a clinical isolate (genotype T4).

RESULTS

Three IS showed being lethal to 100% of the Acanthamoeba trophozoites at the minimum inhibitory concentrations of 125 and 62.5 μg/mL (C₁₆MImMeS), 31.25 and 62.5 μg/mL (C₁₆MImCl), and 125 and 125 μg/mL (C₁₈MImCl) for ATCC30010 and isolate T4, respectively. C₁₆MImNTf2 did not demonstrate amoebicidal activity. All active IS caused the hemolysis of erythrocytes. The cytotoxic effect of the IS was tested in RAW macrophages and human brain microvascular endothelial cells, which demonstrated cytotoxicity in all concentrations tested against both cell lines. As a consequence, these IS with amoebicidal activity presented low selectivity index values (SI) (SI < 1.0), demonstrating lack of parasite selectivity.

CONCLUSION

Thus, C₁₆MImMeS, C₁₆MImCl, and C18MImCl seem to hold greater promise as components for contact lens cleaning and disinfection solutions, instead of direct human application.

Curcuma longa ethanol extract and Curcumin inhibit the growth of Acanthamoeba triangularis trophozoites and cysts isolated from water reservoirs at Walailak University, Thailand

CURCUMA LONGA

(C. longa) rhizome extract has been traditionally used to treat many infections. Curcumin, a pure compound isolated from the plant, has been documented to possess a wide spectrum of pharmacological effects. The present study aimed to investigate the effects of Thai medicinal plant extracts including C. longa extract and Curcumin on Acanthamoeba triangularis, a causative agent of human Acanthamoeba keratitis. The parasite was isolated from the recreational reservoir at Walailak University, Thailand. The organism was identified as A. triangularis using morphology and 18S rDNA nucleotide sequences. The pathogen was tested for their susceptibility to ethanol extracts of Thai medicinal plants based on eye infection treatment. The ethanol C. longa extract showed the strongest anti-Acanthamoeba activity against both the trophozoites and cysts, followed by Coscinium fenestratum, Coccinia grandis, and Acmella oleracea extracts, respectively. After 24 h, 95% reduction of trophozoite viability was significantly decreased following the treatment with C. longa extract at 125 µg/mL, compared with the control (P < 0.05). The extract at 1,000 µg/mL inhibited 90% viability of Acanthamoeba cyst within 24 h, compared with the control. It was found that the cysts treated with C. longa extract at 500 µg/mL demonstrated abnormal shape after 24 h. The MIC values of C. longa extract and Curcumin against the trophozoites were 125 and 62.5 µg/mL, respectively. While the MICs of the extract and curcumin against the cysts were 500 and 1,000 µg/mL, respectively. The results suggested the potential medicinal benefits of C. longa extract and Curcumin as the alternative treatment of Acanthamoeba infections.

Legionella pneumophila and Protozoan Hosts: Implications for the Control of Hospital and Potable Water Systems

Legionella pneumophila is an opportunistic waterborne pathogen of public health concern. It is the causative agent of Legionnaires’ disease (LD) and Pontiac fever and is ubiquitous in manufactured water systems, where protozoan hosts and complex microbial communities provide protection from disinfection procedures. This review collates the literature describing interactions between L. pneumophila and protozoan hosts in hospital and municipal potable water distribution systems. The effectiveness of currently available water disinfection protocols to control L. pneumophila and its protozoan hosts is explored. The studies identified in this systematic literature review demonstrated the failure of common disinfection procedures to achieve long term elimination of L. pneumophila and protozoan hosts from potable water. It has been demonstrated that protozoan hosts facilitate the intracellular replication and packaging of viable L. pneumophila in infectious vesicles; whereas, cyst-forming protozoans provide protection from prolonged environmental stress. Disinfection procedures and protozoan hosts also facilitate biogenesis of viable but non-culturable (VBNC) L. pneumophila which have been shown to be highly resistant to many water disinfection protocols. In conclusion, a better understanding of L. pneumophila-protozoan interactions and the structure of complex microbial biofilms is required for the improved management of L. pneumophila and the prevention of LD.

Investigation of the in vitro cysticidal activity of miltefosine against Acanthamoeba spp

The present study evaluated the in vitro efficacy of miltefosine against cysts of Acanthamoeba spp. belonging to genotypes T3, T4 and T5. Each genotype was incubated with miltefosine at the concentration of 2.42, 4.84, 9.68, 19.36, 38.72 and 77.44 mM for different periods; 1, 3, 5, 7 d at 37 °C. The viability was assessed by staining with 0.4% trypan blue and culturing on NNA medium at 30 °C for 1 month. The results showed 100% eradication of cyst stage of all concentrations, but exhibited a different degree of activity against different genotypes. The MCC of 38.72 mM could kill genotype T4 and T5 after 1 d of incubation, whereas the killing of T3 needed MCC of 77.44 mM at the same incubation time. Miltefosine showed statistically highly significant difference (P < 0.001) in comparison to non-treated control. Although our finding needs to confirm in animal models, this information may be the guideline for optimizing therapy or considered to combine with the other drugs for effective treatment.

Heat and chlorine resistance of a soil Acanthamoeba sp. cysts in water

AIMS

The study established the inactivation kinetic parameters of an Acanthamoeba cyst isolate subjected to heating and chlorination.

METHODS AND RESULTS

A strain of Acanthamoeba was isolated and purified from an area surrounding a pilot food plant. Mature cysts (14 days) were subjected to heat inactivation studies at 71, 76, 81, 86 and 91°C; and chlorination at 100, 200, 300, 400 and 500 ppm. The decimal reduction times (D-values) at 71, 76, 81, 86 and 91°C were 18·31, 9·26, 7·35, 4·52 and 1·81 min respectively. The calculated thermal resistance constant (z-value) was 21·32°C (R²  = 0·96-0·97). The D-value in 100, 200, 300, 400 and 500 ppm chlorine-treated water were 47·17, 25·06, 24·51, 23·70 and 18·55 min respectively. The chlorine resistance constant (z-value) was 1179 ppm chlorine (R²  = 0·65-0·74).

CONCLUSIONS

Results demonstrated high resistance of the isolated Acanthamoeba cysts towards the common methods applied in ensuring food and food processing environment sanitation.

SIGNIFICANCE AND IMPACT OF THE STUDY

The resistance parameters of the test organisms established in this study may be used in the establishment of Sanitation Standard Operating Procedures (SSOPs), which are often based on inactivation of bacteria. These SSOPs could render better protection to food and food processing environments.

First Molecular Evidences of Acanthamoeba T3, T4 and T5 Genotypes in Hemodialysis Units in Iran

BACKGROUND

Acanthamoeba is a genus of the free-living amoeba that is widespread in the environment and is a causative agent of opportunistic infections in human. This study aimed to investigate the existence and genotyping of Acanthamoeba species in hemodialysis units in Iran.

METHODS

In the present study, forty water samples of hydraulic systems and twenty dust samples were collected from two hemodialysis units in Mazandaran Province, northern Iran. The samples were cultivated on non-nutrient agar and genotyping was performed by targeting the 18S rRNA gene.

RESULTS

Both morphology and molecular analyses showed that 17.5% (7/40) of water samples and 50% (10/20) of dust samples were positive for Acanthamoeba spp. The sequencing analysis of these isolates was found to be T3, T4 and T5 genotypes.

DISCUSSION

To the best of our knowledge, this is the first investigation to identify of Acanthamoeba species in hydraulic system of hemodialysis units in Iran. High contamination of hemodialysis units with virulent T4 genotype of Acanthamoeba may poses a risk for biofilm formation. Our results support urgent need to improve filtration methods in dialysis units and monitoring hemodialysis patients for Acanthamoeba infections.

The most abundant cyst wall proteins of Acanthamoeba castellanii are lectins that bind cellulose and localize to distinct structures in developing and mature cyst walls

Background

Acanthamoeba castellanii, which causes keratitis and blindness in under-resourced countries, is an emerging pathogen worldwide, because of its association with contact lens use. The wall makes cysts resistant to sterilizing reagents in lens solutions and to antibiotics applied to the eye.

Methodology/Principal findings

Transmission electron microscopy and structured illumination microscopy (SIM) showed purified cyst walls of A. castellanii retained an outer ectocyst layer, an inner endocyst layer, and conical ostioles that connect them. Mass spectrometry showed candidate cyst wall proteins were dominated by three families of lectins (named here Jonah, Luke, and Leo), which bound well to cellulose and less well to chitin. An abundant Jonah lectin, which has one choice-of-anchor A (CAA) domain, was made early during encystation and localized to the ectocyst layer of cyst walls. An abundant Luke lectin, which has two carbohydrate-binding modules (CBM49), outlined small, flat ostioles in a single-layered primordial wall and localized to the endocyst layer and ostioles of mature walls. An abundant Leo lectin, which has two unique domains with eight Cys residues each (8-Cys), localized to the endocyst layer and ostioles. The Jonah lectin and glycopolymers, to which it binds, were accessible in the ectocyst layer. In contrast, Luke and Leo lectins and the glycopolymers, to which they bind, were mostly inaccessible in the endocyst layer and ostioles.

Conclusions/Significance

The most abundant A. castellanii cyst wall proteins are three sets of lectins, which have carbohydrate-binding modules that are conserved (CBM49s of Luke), newly characterized (CAA of Jonah), or unique to Acanthamoebae (8-Cys of Leo). Cyst wall formation is a tightly choreographed event, in which lectins and glycopolymers combine to form a mature wall with a protected endocyst layer. Because of its accessibility in the ectocyst layer, an abundant Jonah lectin is an excellent diagnostic target.

A half century ago, investigators identified cellulose in the Acanthamoeba cyst wall, which has two layers and conical ostioles that connect them. Here we showed cyst walls contain three large sets of cellulose-binding lectins, which localize to the ectocyst layer (a Jonah lectin) or to the endocyst layer and ostioles (Luke and Leo lectins). We used the lectins to establish a sequence for cyst wall assembly when trophozoites are starved and encyst. In the first stage, a Jonah lectin and glycopolymers were present in dozens of distinct vesicles. In the second stage, a primordial wall contained small, flat ostioles outlined by a Luke lectin. In the third stage, a Jonah lectin remained in the ectocyst layer, while Luke and Leo lectins moved to the endocyst layer and ostioles. A description of the major events during cyst wall development is a starting point for mechanistic studies of its assembly.

Synthesis and in vitro activity of new biguanide-containing dendrimers on pathogenic isolates of Acanthamoeba polyphaga and Acanthamoeba griffini

The genus Acanthamoeba can cause Acanthamoeba keratitis (AK) and granulomatous amoebic encephalitis (GAE). The treatment of these illnesses is hampered by the existence of a resistance stage that many times causes infection relapses. In an attempt to add new agents to our chemotherapeutic arsenal against acanthamebiasis, two Acanthamoeba isolates were treated in vitro with newly synthesized biguanide dendrimers. Trophozoite viability analysis and ultrastructural studies showed that dendrimers prevent encystment by lysing the cellular membrane of the amoeba. Moreover, one of the dendrimers showed low toxicity when tested on mammalian cell cultures, which suggest that it might be eventually used as an amoebicidal drug or as a disinfection compound in contact lens solutions.

Extracellular Vesicles from the Protozoa Acanthamoeba castellanii: Their Role in Pathogenesis, Environmental Adaptation and Potential Applications

Extracellular vesicles (EVs) are membranous compartments of distinct cellular origin and biogenesis, displaying different sizes and include exosomes, microvesicles, and apoptotic bodies. The EVs have been described in almost every living organism, from simple unicellular to higher evolutionary scale multicellular organisms, such as mammals. Several functions have been attributed to these structures, including roles in energy acquisition, cell-to-cell communication, gene expression modulation and pathogenesis. In this review, we described several aspects of the recently characterized EVs of the protozoa Acanthamoeba castellanii, a free-living amoeba (FLA) of emerging epidemiological importance, and compare their features to other parasites' EVs. These A. castellanii EVs are comprised of small microvesicles and exosomes and carry a wide range of molecules involved in many biological processes like cell signaling, carbohydrate metabolism and proteolytic activity, such as kinases, glucanases, and proteases, respectively. Several biomedical applications of these EVs have been proposed lately, including their use in vaccination, biofuel production, and the pharmaceutical industry, such as platforms for drug delivery.

3D Hydrogels Containing Interconnected Microchannels of Subcellular Size for Capturing Human Pathogenic Acanthamoeba Castellanii

Porous hydrogel scaffolds are ideal candidates for mimicking cellular microenvironments, regarding both structural and mechanical aspects. We present a novel strategy to use uniquely designed ceramic networks as templates for generating hydrogels with a network of interconnected pores in the form of microchannels. The advantages of this new approach are the high and guaranteed interconnectivity of the microchannels, as well as the possibility to produce channels with diameters smaller than 7 μm. Neither of these assets can be ensured with other established techniques. Experiments using the polyacrylamide substrates produced with our approach have shown that the migration of human pathogenic Acanthamoeba castellanii trophozoites is manipulated by the microchannel structure in the hydrogels. The parasites can even be captured inside the microchannel network and removed from their incubation medium by the porous polyacrylamide, indicating the huge potential of our new technique for medical, pharmaceutical, and tissue engineering applications.

Isolation, identification of pathogenic Acanthamoeba from drinking and recreational water sources in Saudi Arabia

Objective:

The present study was conducted to isolate and identify the Acanthamoeba species from various water sources such as drinking water, tap water, swimming pool, and other recreational water.

Materials and methods:

During the study period, 57 water samples were collected from various sources such as tap water, drinking water, swimming pool, and recreational water. All samples were processed and cultured on non-nutrient agar medium (NNA) with Escherichia coli overlay for the isolation of Acanthamoeba species. Organism identified based on the microscopic morphology of cyst and trophozoites forms. The pathogenicity of Acanthamoeba was analyzed by thermotolerance and osmotolerance assays.

Results:

Acanthamoeba were detected in 10 out of 57 (17.5%) examined water samples. The high percentage of positivity was observed in bore well water stored in tanks (37.5%) and in recreational water samples (26.7%). All processed drinking water samples were free from Acanthamoeba. Based on pathogenicity test assays, four (40%) were pathogenic and three (30%) were non-pathogenic. The observed frequency of Acanthamoeba spp. was compared with available literature worldwide.

Conclusion:

This study is the first report showing the distribution of Acanthamoeba in various water sources in the central region of Saudi Arabia and confirms that the high percentage presence of pathogenic strains in recreational water could threat contact lens wearers. Further research works are required to identify the prevalence of pathogenic Acanthamoeba from various water sources in Saudi Arabia.

Concomitant inactivation of Acanthamoeba spp. and Escherichia coli using suspended and immobilized TiO2

This work reports the application of photocatalytic disinfection to the inactivation of Acanthamoeba trophozoites, a free-living pathogenic amoeba. Two types of photocatalytic reactors configurations have been used: i) a slurry reactor using suspended titanium dioxide (TiO₂); and, ii) a fixed-bed reactor using immobilized TiO₂ onto glass Raschig rings. The effect of the chemical composition of water has been analysed, comparing the efficiency of the process in deionized water (DW) and synthetic wastewater treatment plant effluent (SWTPE). The inactivation of Acanthamoeba spp. has been compared to that of Escherichia coli bacteria, being also analysed the concomitant inactivation of both microorganisms. Our results show that 99% of inactivation of E. coli and Acanthamoeba spp. can be achieved using photocatalysis in both reactor configurations, but interestingly, the kinetics of inactivation of both microorganisms together differs from that found with them separately. Particularly, E. coli seems to be more resistant to the inactivation in the presence of Acanthamoeba spp. which has been justified by the screen effect caused by the bigger size of Acanthamoeba spp. This observation is more pronounced in DW as the composition of the SWTPE prevent the microorganisms from suffering osmotic and/or mechanical stress and protect cellular structures to the attack of reactive oxygen species (ROS). On the other hand, the difference between the inactivation rate of E. coli and Acanthamoeba, points out the importance of the different inactivation mechanisms, suggesting that the entry of small TiO₂ particles into the cytoplasm of the Acanthamoeba cells provokes the attack of inner structures and as a consequence a faster inactivation. This mechanism is not possible when the catalyst is immobilized leading to a higher cell resistance to inactivation and consequently lower efficiency of the disinfection process.

Identification and ultrastructural characterization of Acanthamoeba bacterial endocytobionts belonging to the Alphaproteobacteria class

The detection and identification of two endocytobiotic bacterial strains, one affiliated to the “Candidatus Caedibacter acanthamoebae”/“Ca. Paracaedimonas acanthamoeba”, and another to the endosymbiont of Acanthamoeba UWC8 and “Ca. Jidaibacter acanthamoeba” are described. For endocytobiont screening, we developed a PCR method with a set of broad-range bacterial 16S rRNA primers to substitute the commonly used but technically demanding fluorescent in situ hybridization technique. Our PCR test alone without sequencing failed to discriminate the endocytobiont-containing and endocytobiont-free Acanthamoeba sp. due to the presence of mismatched primers to host mitochondrial DNA. We highlighted the need to perform bacterial primer checking against the Acanthamoeba genome to avoid false positive detection in PCR. Although the genetic aspect of “Ca. Caedibacter acanthamoebae”/“Ca. Paracaedimonas acanthamoeba” and the endosymbiont of Acanthamoeba UWC8/“Ca. Jidaibacter acanthamoeba” are well studied, knowledge pertaining to their morphologies are quite vague. Hence, we used transmission electron microscopy to examine our endocytobionts which are affiliated to previously described intracellular bacteria of Acanthamoeba sp. We used good-quality TEM images for the localization and the fate of the current endocytobionts inside different life stages of the hosts. Furthermore, to the best of our knowledge, our TEM findings are the first to provide morphological evidence for the clearance of defective Acanthamoeba endocytobionts via an autophagic-like process.

Horizontal transmission of Endolimax piscium, causative agent of systemic amoebiasis in Senegalese sole Solea senegalensis

Systemic amoebiasis of Senegalese sole Solea senegalensis is caused by Endolimax piscium Constenla, Padrós & Palenzuela, 2014 a cryptic parasitic member of the Archamoebae whose epidemiology is yet unknown. To test whether the parasite can be transmitted horizontally, an experimental trial by cohabitation between non-infected and infected fish was designed. Transmission of the parasite from naturally infected to healthy fish was confirmed in the experiment, with the water as the most likely route of infection. Under the conditions of the study, the infection process was remarkably slow, as parasites could be detected by in situ hybridization within the intestinal mucosa of recipient fish only after 17 wk of cohabitation, and none of the new hosts displayed clinical signs of disease. Long prepatent period and the need for additional triggering factors for the development of the clinical condition are suggested. The intestinal mucosa is proposed as the tissue where the amoeba can survive as endocommensal, but also as an invasion route from which the parasite would disperse to other organs.

Enrichment of free-living amoebae in biofilms developed at upper water levels in drinking water storage towers: An inter- and intra-seasonal study

Free-living amoebae (FLA) are ubiquitous organisms present in various natural and artificial environments, such as drinking water storage towers (DWST). Some FLA, such as Acanthamoeba sp., Naegleria fowleri, and Balamuthia mandrillaris, can cause severe infections at ocular or cerebral level in addition to being potential reservoirs of other pathogens. In this work, the abundance and diversity of FLA was evaluated in two sampling campaigns: one performed over five seasons in three DWST at three different levels (surface, middle and bottom) in water and biofilm using microscopy and PCR, and one based on the kinetics analysis in phase contrast and confocal microscopy of biofilm samples collected every two weeks during a 3-month period at the surface and at the bottom of a DWST. In the seasonal study, the FLA were detected in each DWST water in densities of ~20 to 25amoebaeL^-1. A seasonal variation of amoeba distribution was observed in water samples, with maximal densities in summer at ~30amoebaeL^-1 and minimal densities in winter at ~16amoebaeL^-1. The FLA belonging to the genus Acanthamoeba were detected in two spring sampling campaigns, suggesting a possible seasonal appearance of this potentially pathogenic amoeba. Interestingly, a 1 log increase of amoebae density was observed in biofilm samples collected at the surface of all DWST compared to the middle and the bottom where FLA were at 0.1-0.2amoebae/cm². In the kinetics study, an increase of amoebae density, total cell density, and biofilm thickness was observed as a function of time at the surface of the DWST, but not at the bottom. To our knowledge, this study describes for the first time a marked higher FLA density in biofilms collected at upper water levels in DWST, constituting a potential source of pathogenic micro-organisms.