War of the microbial world: Acanthamoeba spp. interactions with microorganisms

The influence of amoeba metal homeostasis on antifungal activity against Cryptococcus gattii

Free-living amoebas are natural predators of fungi, including human pathogens of the Cryptococcus genus. To survive and proliferate inside phagocytes, cryptococcal cells must acquire several nutrients. Zinc is fundamental for all life forms and develops a crucial role in the virulence of fungal pathogens, phagocytes reduce the availability of this metal to reduce the development of infection. The Acanthamoeba castellanii ACA1_271600 gene codes a metal transporter that is possibly associated with such antifungal strategy. Here, we evaluated the impact of A. castellanii metal homeostasis on C. gattii survival. Gene silencing of ACA1_271600 was performed and the interaction outcome of amoeba cells with both WT and zinc homeostasis-impaired mutant cryptococcal cells was evaluated. Decreased levels of ACA1_271600 in silenced amoeba cells led to higher proliferation of such cryptococcal strains. This effect was more pronounced in the zip1 mutant of C. gattii, suggesting that ACA1_271600 gene product modulates metal availability in Cryptococcus-infected amoebae. In addition, a systems biology analysis allowed us to infer that ACA1_271600 may also be involved in other biological processes that could compromise amoebae activity over cryptococcal cells. These results support the hypothesis that A. castellanii can apply nutritional immunity to hamper cryptococcal survival.

Comprehensive characterization of extracellular vesicles produced by environmental (Neff) and clinical (T4) strains of Acanthamoeba castellanii

We conducted a comprehensive comparative analysis of extracellular vesicles (EVs) from two Acanthamoeba castellanii strains, Neff (environmental) and T4 (clinical). Morphological analysis via transmission electron microscopy revealed slightly larger Neff EVs (average = 194.5 nm) compared to more polydisperse T4 EVs (average = 168.4 nm). Nanoparticle tracking analysis (NTA) and dynamic light scattering validated these differences. Proteomic analysis of the EVs identified 1,352 proteins, with 1,107 common, 161 exclusive in Neff, and 84 exclusively in T4 EVs. Gene ontology and Kyoto Encyclopedia of Genes and Genomes (KEGG) mapping revealed distinct molecular functions and biological processes and notably, the T4 EVs enrichment in serine proteases, aligned with its pathogenicity. Lipidomic analysis revealed a prevalence of unsaturated lipid species in Neff EVs, particularly triacylglycerols, phosphatidylethanolamines (PEs), and phosphatidylserine, while T4 EVs were enriched in diacylglycerols and diacylglyceryl trimethylhomoserine, phosphatidylcholine and less unsaturated PEs, suggesting differences in lipid metabolism and membrane permeability. Metabolomic analysis indicated Neff EVs enrichment in glycerolipid metabolism, glycolysis, and nucleotide synthesis, while T4 EVs, methionine metabolism. Furthermore, RNA-seq of EVs revealed differential transcript between the strains, with Neff EVs enriched in transcripts related to gluconeogenesis and translation, suggesting gene regulation and metabolic shift, while in the T4 EVs transcripts were associated with signal transduction and protein kinase activity, indicating rapid responses to environmental changes. In this novel study, data integration highlighted the differences in enzyme profiles, metabolic processes, and potential origins of EVs in the two strains shedding light on the diversity and complexity of A. castellanii EVs and having implications for understanding host-pathogen interactions and developing targeted interventions for Acanthamoeba-related diseases.IMPORTANCEA comprehensive and fully comparative analysis of extracellular vesicles (EVs) from two Acanthamoeba castellanii strains of distinct virulence, a Neff (environmental) and T4 (clinical), revealed striking differences in their morphology and protein, lipid, metabolites, and transcripts levels. Data integration highlighted the differences in enzyme profiles, metabolic processes, and potential distinct origin of EVs from both strains, shedding light on the diversity and complexity of A. castellanii EVs, with direct implications for understanding host-pathogen interactions, disease mechanisms, and developing new therapies for the clinical intervention of Acanthamoeba-related diseases.

Metagenomics insights into microbiome and antibiotic resistance genes from free living amoeba in chlorinated wastewater effluents

Free living amoeba (FLA) are among the organisms commonly found in wastewater and are well-established hosts for diverse microbial communities. Despite its clinical significance, there is little knowledge on the FLA microbiome and resistome, with previous studies relying mostly on conventional approaches. In this study we comprehensively analyzed the microbiome, antibiotic resistome and virulence factors (VFs) within FLA isolated from final treated effluents of two wastewater treatment plants (WWTPs) using shotgun metagenomics. Acanthamoeba has been identified as the most common FLA, followed by Entamoeba. The bacterial diversity showed no significant difference (p > 0.05) in FLA microbiomes obtained from the two WWTPs. At phylum level, the most dominant taxa were Proteobacteria, followed by Firmicutes and Actinobacteria. The most abundant genera identified were Enterobacter followed by Citrobacter, Paenibacillus, and Cupriavidus. The latter three genera are reported here for the first time in Acanthamoeba. In total, we identified 43 types of ARG conferring resistance to cephalosporins, phenicol, streptomycin, trimethoprim, quinolones, cephalosporins, tigecycline, rifamycin, and kanamycin. Similarly, a variety of VFs in FLA metagenomes were detected which included flagellar proteins, Type IV pili twitching motility proteins (pilH and rpoN), alginate biosynthesis genes AlgI, AlgG, AlgD and AlgW and Type VI secretion system proteins and general secretion pathway proteins (tssM, tssA, tssL, tssK, tssJ, fha, tssG, tssF, tssC and tssB, gspC, gspE, gspD, gspF, gspG, gspH, gspI, gspJ, gspK, and gspM). To the best of our knowledge, this is the first study of its kind to examine both the microbiomes and resistome in FLA, as well as their potential pathogenicity in treated effluents. Additionally, this study showed that FLA can host a variety of potentially pathogenic bacteria including Paenibacillus, and Cupriavidus that had not previously been reported, indicating that their relationship may play a role in the spread and persistence of antibiotic resistant bacteria (ARBs) and antibiotic resistance genes (ARGs) as well as the evolution of novel pathogens.

Inhibitory and anti-adherent effects of Piper betle L. leaf extract against Acanthamoeba triangularis in co-infection with Staphylococcus aureus and Pseudomonas aeruginosa: A sustainable one-health approach

Background and Aim

Keratitis is a serious ocular infection often caused by pathogenic microorganisms such as Acanthamoeba spp. Among other harmful microbes, Acanthamoeba keratitis presents a particular challenge due to its resistance to conventional antimicrobial agents. Piper betle Linn., commonly known as betel leaf, has been traditionally used for its medicinal properties. This study aimed to assess the potential of the leaf ethanol extract of P. betle Linn. in the treatment of Acanthamoeba triangularis in monoculture and co-culture with two prevalent pathogenic bacteria, Staphylococcus aureus and Pseudomonas aeruginosa, associated with keratitis.

Materials and Methods

Minimum inhibitory concentrations (MICs) of A. triangularis, S. aureus, and P. aeruginosa extracts in monoculture and coinfected conditions were examined. In addition, this study explored the potential of the extract in preventing Acanthamoeba adherence in both monoculture and co-culture environments. Scanning electron microscopy (SEM) analysis confirmed the impact of the extract on Acanthamoeba cell membranes, including acanthopodia. Furthermore, a time-kill kinetic assay was used to validate the amoebicidal activity of the extract against A. triangularis and the tested bacteria.

Results

MICs for trophozoites, cysts, P. aeruginosa, and S. aureus in the monoculture were 0.25, 0.25, 0.51, and 0.128 mg/mL, respectively, whereas the MICs for Acanthamoeba coinfected with bacteria were higher than those in the monoculture. This extract inhibited the growth of A. triangularis trophozoites and cysts for up to 72 h. Moreover, P. betle extract effectively prevented the adherence of Acanthamoeba to contact lenses under monoculture conditions. SEM analysis confirmed that P. betle extract affects the cell membrane of Acanthamoeba, including Acanthopodia. In addition, the time-kill kinetic assay confirmed that the extract contained amoebicidal activity against A. triangularis, including the tested bacteria. Notably, S. aureus was more susceptible than A. triangularis and P. aeruginosa to P. betle extract treatment. Unexpectedly, our study revealed that S. aureus negatively affected A. triangularis in the co-culture after 3 days of incubation, whereas P. aeruginosa facilitated the growth of A. triangularis in the presence of the extract.

Conclusion

This study provides compelling evidence of the anti-adhesive and anti-Acanthamoeba properties of P. betle leaf extract against A. triangularis under monoculture and co-culture conditions. The observed impact on Acanthamoeba cell membranes, coupled with the time-kill kinetic assay results, underscores the potential of P. betle leaf extract as a promising agent for combating Acanthamoeba-related infections in humans and animals.

The consequences of viral infection on protists

Protists encompass a vast widely distributed group of organisms, surpassing the diversity observed in metazoans. Their diverse ecological niches and life forms are intriguing characteristics that render them valuable subjects for in-depth cell biology studies. Throughout history, viruses have played a pivotal role in elucidating complex cellular processes, particularly in the context of cellular responses to viral infections. In this comprehensive review, we provide an overview of the cellular alterations that are triggered in specific hosts following different viral infections and explore intricate biological interactions observed in experimental conditions using different host-pathogen groups.

Self-assembled micelles loaded with itraconazole as anti-Acanthamoeba nano-formulation

Acanthamoeba castellanii are opportunistic pathogens known to cause infection of the central nervous system termed: granulomatous amoebic encephalitis, that mostly effects immunocompromised individuals, and a sight threatening keratitis, known as Acanthamoeba keratitis, which mostly affects contact lens wearers. The current treatment available is problematic, and is toxic. Herein, an amphiphilic star polymer with AB2 miktoarms [A = hydrophobic poly(ℇ-Caprolacton) and B = hydrophilic poly (ethylene glycol)] was synthesized by ring opening polymerization and CuI catalyzed azide-alkyne cycloaddition. Characterization by 1H and 13C NMR spectroscopy, size-exclusion chromatography and fluorescence spectroscopy was accomplished. The hydrophobic drug itraconazole (ITZ) was incorporated in self-assembled micellar structure of AB2 miktoarms through co-solvent evaporation. The properties of ITZ loaded (ITZ-PCL-PEG2) and blank micelles (PCL-PEG2) were investigated through zeta sizer, scanning electron microscopy and Fourier-transform infrared spectroscopy. Itraconazole alone (ITZ), polymer (DPB-PCL), empty polymeric micelles (PCL-PEG2) alone, and itraconazole loaded in polymeric micelles (ITZ-PCL-PEG2) were tested for anti-amoebic potential against Acanthamoeba, and the cytotoxicity on human cells were determined. The polymer was able to self-assemble in aqueous conditions and exhibited low value for critical micelle concentration (CMC) 0.05-0.06 µg/mL. The maximum entrapment efficiency of ITZ was 68%. Of note, ITZ, DPB, PCL-PEG2 and ITZ-PCL-PEG2 inhibited amoebae trophozoites by 37.34%, 36.30%, 35.77%, and 68.24%, respectively, as compared to controls. Moreover, ITZ-PCL-PEG2 revealed limited cytotoxicity against human keratinocyte cells. These results are indicative that ITZ-PCL-PEG2 micelle show significantly better anti-amoebic effects as compared to ITZ alone and thus should be investigated further in vivo to determine its clinical potential.

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

PURPOSE

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

METHODS

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

RESULTS

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

CONCLUSION

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

Influence of salt and temperature in the growth of pathogenic free-living amoebae

Introduction

Free-living amoebae are an extensive group of protistans that can be found in a wide variety of environments. Among them, the Acanthamoeba genus and Naegleria fowleri stand out as two of the most pathogenic amoebae and with a higher number of reported cases. N. fowleri is mainly found in warm freshwater water bodies whereas amoebae of the Acanthamoeba genus are broadly distributed through natural and anthropogenic environments. In this regard, the management and the control of the amoebic populations in swimming pools has become a major public health challenge for institutions.

Methods

The aim of this work was to evaluate the growth pattern of trophozoites of A. griffini and N. fowleri at different temperatures and salt concentrations.

Results and discussion

Our results showed that A. griffini resisted a higher concentration of salt than N. fowleri. Moreover, no trophozoites could withstand the salt levels of the sea in in vitro conditions. This work supports the contention that salinity could represent an important and useful tool for the control of the most pathogenic amoebic populations in recreational water bodies.

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.

Induction of Programmed Cell Death in Acanthamoeba culbertsoni by the Repurposed Compound Nitroxoline

Acanthamoeba is a ubiquitous genus of amoebae that can act as opportunistic parasites in both humans and animals, causing a variety of ocular, nervous and dermal pathologies. Despite advances in Acanthamoeba therapy, the management of patients with Acanthamoeba infections remains a challenge for health services. Therefore, there is a need to search for new active substances against Acanthamoebae. In the present study, we evaluated the amoebicidal activity of nitroxoline against the trophozoite and cyst stages of six different strains of Acanthamoeba. The strain A. griffini showed the lowest IC50 value in the trophozoite stage (0.69 ± 0.01 µM), while the strain A. castellanii L-10 showed the lowest IC50 value in the cyst stage (0.11 ± 0.03 µM). In addition, nitroxoline induced in treated trophozoites of A. culbertsoni features compatibles with apoptosis and autophagy pathways, including chromatin condensation, mitochondrial malfunction, oxidative stress, changes in cell permeability and the formation of autophagic vacuoles. Furthermore, proteomic analysis of the effect of nitroxoline on trophozoites revealed that this antibiotic induced the overexpression and the downregulation of proteins involved in the apoptotic process and in metabolic and biosynthesis pathways.

Novel anti-Acanthamoebic properties of raloxifene sulfonate/sulfamate derivatives

Acanthamoeba are known to cause a vision threatening eye infection typically due to contact lens wear, and an infection of the central nervous system. The ability of these amoebae to switch phenotypes, from an active trophozoite to a resistant cyst form is not well understood; the cyst stage is often resistant to chemotherapy, which is of concern given the rise of contact lens use and the ineffective disinfectants available, versus the cyst stage. Herein, for the first time, a range of raloxifene sulfonate/sulfamate derivatives which target nucleotide pyrophosphatase/phosphodiesterase enzymes, were assessed using amoebicidal and excystation tests versus the trophozoite and cyst stage of Acanthamoeba. Moreover, the potential for cytopathogenicity inhibition in amoebae was assessed. Each of the derivatives showed considerable anti-amoebic activity as well as the ability to suppress phenotypic switching (except for compound 1a). Selected raloxifene derivatives reduced Acanthamoeba-mediated host cell damage using lactate dehydrogenase assay. These findings suggest that pyrophosphatase/phosphodiesterase enzymes may be valuable targets against Acanthamoeba infections.

Identification and quantification of Acanthamoeba spp. within seawater at four coastal lagoons on the east coast of Australia

Acanthamoeba is an opportunistic free-living heterotrophic protist that is the most predominant amoeba in diverse ecological habitats. Acanthamoeba causes amoebic keratitis (AK), a painful and potentially blinding corneal infection. Major risk factors for AK have been linked to non-optimal contact lens hygiene practices and Acanthamoeba contamination of domestic and recreational water. This study investigated the incidence and seasonal variation of Acanthamoeba spp. within coastal lagoons located on the eastern coast of Australia and then examined the association between Acanthamoeba and water abiotic factors and bacterial species within the water. Water samples were collected from four intermittently closed and open lagoons (ICOLLs) (Wamberal, Terrigal, Avoca and Cockrone) every month between August 2019 to July 2020 except March and April. qPCR was used to target the Acanthamoeba 18S rRNA gene, validated by Sanger sequencing. Water abiotic factors were measured in situ using a multiprobe metre and 16S rRNA sequencing (V3-V4) was performed to characterise bacterial community composition. Network analysis was used to gauge putative associations between Acanthamoeba incidence and bacterial amplicon sequence variants (ASVs). Among 206 water samples analysed, 79 (38.3%) were Acanthamoeba positive and Acanthamoeba level was significantly higher in summer compared with winter, spring, or autumn (p = 0.008). More than 50% (23/45) water samples of Terrigal were positive for Acanthamoeba which is a highly urbanised area with extensive recreational activities while about 32% (16/49) samples were positive from Cockrone that is the least impacted lagoon by urban development. All sequenced strains belonged to the pathogenic genotype T4 clade except two which were of genotype clades T2 and T5. Water turbidity, temperature, intl1 gene concentration, and dissolved O2 were significantly associated with Acanthamoeba incidence (p < 0.05). The ASVs level of cyanobacteria, Pseudomonas spp., Candidatus spp., and marine bacteria of the Actinobacteria phylum and Acanthamoeba 18S rRNA genes were positively correlated (Pearson's r ≥ 0.14). The presence of Acanthamoeba spp. in all lagoons, except Wamberal, was associated with significant differences in the composition of bacterial communities (beta diversity). The results of this study suggest that coastal lagoons, particularly those in urbanised regions with extensive water recreational activities, may pose an elevated risk to human health due to the relatively high incidence of pathogenic Acanthamoeba in the summer. These findings underscore the importance of educating the public about the rare yet devastating impact of AK on vision and quality of life, highlighting the need for collaborative efforts between public health officials and educators to promote awareness and preventive measures, especially focusing lagoons residents and travellers.

Nonribosomal peptides protect Pseudomonas nunensis 4A2e from amoebal and nematodal predation

The rhizosphere is a highly competitive environment forcing bacteria to evolve strategies to oppose their enemies. The production of toxic secondary metabolites allows bacteria to counteract predators. In this study, we describe the anti-predator armamentarium of the soil-derived bacterium Pseudomonas nunensis 4A2e. Based on a genome mining approach, we identified several biosynthetic gene clusters coding for nonribosomal peptide synthetases. Generation of gene deletion mutants of the respective clusters shows a loss of defense capabilities. We isolated the novel lipopeptides keanumycin D and nunapeptins B and C, and fully elucidated their structures by a combination of in-depth mass spectrometry experiments, stable isotope labelling, and chemical synthesis. Additionally, investigation of the quorum sensing-dependent biosynthesis allowed us to elucidate parts of the underlying regulation of the biosynthetic machinery. Ecology-inspired bioassays highlight the role of these peptides as a defence strategy against protozoans and led us to find a previously unknown function against the bacterivorous nematode Oscheius myriophilus.

Exposure to sublethal concentrations of chlorine enhances the cytotoxicity of Acanthamoeba castellanii

Free-living amoebae belonging to the genus Acanthamoeba are the causative agents of infections in humans and animals. Many studies are being conducted to find effective compounds against amoebae, but their sublethal concentration effects on surviving amoebae seem to have been overlooked. Chlorine is a common disinfection agent commonly added to public water facilities and supplies. In this study, the cytopathic and phagocytic properties of Acanthamoeba castellanii trophozoites following exposure to sublethal concentrations of chlorine were examined. Two hours of exposure to 5 ppm hypochlorite calcium was considered the sublethal concentration for A. castellanii trophozoites. To compare the pathogenic potential of treated and untreated Acanthamoeba trophozoites, cytotoxicity, adhesion assays in RAW 264.7 macrophages, osmo, and thermotolerance tests were carried out. Bacterial uptake was assessed in treated cells to evaluate their phagocytic characteristics. Oxidative stress biomarkers and antioxidant activities were compared in treated and untreated trophozoites. Finally, the mRNA expression of the mannose-binding protein (MBP), cysteine protease 3 (CP3), and serine endopeptidase (SEP) genes was determined in cells. In all the experiments, untreated trophozoites were considered the control. In comparison to untreated trophozoites, in chlorine-treated trophozoites, cytopathic effects were more extensive and resulted in the detachment of macrophage monolayers. Treated trophozoites could not grow at high temperatures (43 °C). Besides, they showed osmotolerance to 0.5 M D-mannitol but not to 1 M. Results demonstrated a higher bacterial uptake rate by chlorine-treated trophozoites than untreated cells. The treated and untreated cells had significantly different glutathione and glutathione/glutathione disulfide ratios. Antioxidant enzyme activities, total antioxidant capacity, and malondialdehyde levels were increased significantly in chlorine-treated cells. Quantifying mRNA expression in chlorine-treated trophozoites revealed that virulence genes were upregulated. Chlorine can form resistance and virulent amoebae if it is not used at a proper concentration and exposure time. Identification of stress responses, their mechanisms in Acanthamoeba, and their relation to amoeba virulence would give us a better perception of their pathophysiology.

The impact of environmental factors on the transport and survival of pathogens in agricultural soils from karst areas of Yunnan province, China: Laboratory column simulated leaching experiments

Introduction

Groundwater is considered the best candidate for drinking water supply in the karst area. The groundwater water resources, however, are vulnerable to pathogenic microorganism contamination because of the typically thin soil layers overlying aquifers and the high permeability of the aquifer host rock, resulting in short residence times and low natural attenuation capacities. Until now, little attention has been paid to the critical environmental factors affecting the pathogenic microorganism contamination in soil-groundwater systems in the karst area.

Methods

In the study, orthogonality column experiments with controlling ambient temperatures, pH values of inlet water, and soil porosities were carried out to investigate the transport and lifespan of pathogenic microorganisms in the leachate of agricultural soils in the karst area of Yunnan province, China. The pathogenic indicators, i.e., total bacteria count (TBC) and total coliforms count (TCC), and hydrochemical parameters, i.e., pH and permanganate index (CODMn) in the leaching water, were systematically monitored.

Results and Discussion

The results showed that bacteria including coliforms can survive for prolonged periods of time in karst soils. The soils overlying the karst rocks were unable to impede the bacteria from seeping into the groundwater. The soils, in turn, likely served as both reservoirs and incubators for pathogenic bacteria. The ambient temperature was the most predominant influential factor affecting both TBC and TCC. The bacteria concentrations were proportional to the temperature in the leachate. Therefore, more attention should be paid to temperature variations in protecting the water supply, particularly in the high-temperature period, such as during the summer months.

Characterization of a Pseudokeronopsis Strain (Ciliophora, Urostylida) and Its Bacterial Endosymbiont “Candidatus Trichorickettsia” (Alphaproteobacteria, Rickettsiales)

Symbiotic associations between bacteria and ciliate protists are rather common. In particular, several cases were reported involving bacteria of the alphaproteobacterial lineage Rickettsiales, but the diversity, features, and interactions in these associations are still poorly understood. In this work, we characterized a novel ciliate protist strain originating from Brazil and its associated Rickettsiales endosymbiont by means of live and ultrastructural observations, as well as molecular phylogeny. Though with few morphological peculiarities, the ciliate was found to be phylogenetically affiliated with Pseudokeronopsis erythrina, a euryhaline species, which is consistent with its origin from a lagoon with significant spatial and seasonal salinity variations. The bacterial symbiont was assigned to “Candidatus Trichorickettsia mobilis subsp. hyperinfectiva”, being the first documented case of a Rickettsiales associated with urostylid ciliates. It resided in the host cytoplasm and bore flagella, similarly to many, but not all, conspecifics in other host species. These findings highlight the ability of “Candidatus Trichorickettsia” to infect multiple distinct host species and underline the importance of further studies on this system, in particular on flagella and their regulation, from a functional and also an evolutionary perspective, considering the phylogenetic proximity with the well-studied and non-flagellated Rickettsia.

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.

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.

Research progress in the Helicobacter pylori with viable non-culturable state

Helicobacter pylori (H. pylori) is one of the most common pathogens in human beings and it is responsible for diseases such as chronic gastritis, peptic ulcer, and even gastric cancer. Studies in recent years have found that H. Pylori could transform from the normal spiral-shaped bacillary form into the coccoid form and enter a viable but non-culturable (VBNC) state, which may pose a potential threat to public health. In this state,the morphological structure and physiological characteristics of H. Pylori have changed. It can maintain the metabolic activity but protein expression is decreased. And the H. Pylori in this state cannot grow in the culture medium. Conditions such as environmental factors, antibiotics, and inhibitors can induce H. Pylori to enter the VBNC state, but it is still not known whether H. pylori in the VBNC state can reactivate or not. Based on the cell membrane integrity and metabolic activity of H. pylori in the VBNC state, it can be detected by classical methods including direct microscopy of live bacteria and molecular biological methods such as reverse transcription-polymerase chain reaction. H. pylori in the VBNC state has been detected in water source and biological media. It has been also found that H. pylori can enter the VBNC state in artificially contaminated food, which poses challenges to public health and food safety. Therefore, it is of great significance to study the change pattern and detection methods of H. pylori in the VBNC state for the prevention and control of H. pylori in the VBNC state. It is valuable to further study the underlying mechanisms of H. pylori in the VBNC state.