Identification of differential protein recognition pattern between Naegleria fowleri and Naegleria lovaniensis

Advancing the understanding of Naegleria fowleri: Global epidemiology, phylogenetic analysis, and strategies to combat a deadly pathogen

Naegleria fowleri is a rare but deadly pathogen that has emerged as an important global public health concern. The pathogen induces primary amoebic meningoencephalitis (PAM), a rapidly progressive and almost always fatal life-threatening brain infection. The devastating impact of N. fowleri and the high mortality rate underscores a deeper understanding and the development of innovative strategies to tackle this issue. Despite various studies that have been conducted on N. fowleri, a comprehensive review that integrates recent findings and addresses critical gaps in understanding remains lacking. This review provides a detailed overview of N. fowleri epidemiology, transmission dynamics, phylogenetic diversity, state-of-the-art diagnostic techniques, therapeutic approaches, and preventive measures. We identified 488 PAM cases globally, reported since 1962, with the highest numbers in the US, Pakistan, and Australia. A phylogenetic analysis of 41 N. fowleri ITS-1, 5.8S, ITS-2 region-based sequences showed genotypic diversity, with genotypes II and III being the most prevalent in Asia, North America, and Europe. Effective approaches to preventing N. fowleri transmission include applying free chlorine to water in storage tanks, taking precautions while swimming, and performing ablution with sterilized water (e.g., boiled or distilled) while avoiding deep inhalation of water, especially in regions with high water contamination. This review highlights the global impact of N. fowleri, future surveillance strategies, prompt diagnosis, potential therapeutic options, and vaccine development to prevent PAM outbreaks. It highlights the importance of joint government and public health efforts to combat this deadly pathogen.

Identification of Naegleria fowleri antigens recognized by serum antibodies from people of Mexicali Valley, México

Naegleria fowleri is an amoeba that causes a fatal disease in the central nervous system known as primary amoebic meningoencephalitis (PAM) in humans. Most of the infections are acquired by people who practice recreational activities in water contaminated with trophozoites. Swimming and wading in irrigation channels of Mexicali are common practices for local people. Although there are some warning signposts in the surrounding sites, people continue using these channels for recreational purposes. In that region, cases of PAM have been reported; however, not everyone who comes into contact with contaminated water containing trophozoites becomes infected, and the factors influencing their immune response to N. fowleri remain unknown. We analyzed the levels of antibodies against N. fowleri in two groups: local individuals, including visitors who swam in the Mexicali channels, and a group from Mexico City (CDMX). In both groups, specific antibody responses were analyzed using immunoassays, including Western blot, ELISA, and cytochemistry. The highest levels of both IgG and IgA were found in samples from Mexicali, compared to those from CDMX. In both groups, IgG recognized polypeptide bands from N. fowleri at molecular weights of 100, 50, and 19 kDa, bands that we have already reported as immunogenic. Moreover, the IgG subjects recognized trophozoite structures such as membrane, pseudopodia, food cups, and even small like-vesicles. This antibody immune response directed against these polypeptide bands and trophozoite structures along with other factors could be participating in the defense of these people against PAM.

Cloning of nf-profilin and intercellular interaction with nf-actin in Naegleria fowleri cysts

Naegleria fowleri is a free-living amoeba found in lakes, soil, hot springs, and poorly chlorinated swimming pools. It is pathogenic to humans, causing a rare and fatal brain infection known as primary amoebic meningoencephalitis (PAM). A previous study utilized RNA-seq analysis to examine genes expressed in N. fowleri cysts and trophozoites, focusing on the nf-profilin gene, which showed high expression in cysts. Profilin is a small actin-binding protein that regulates nf-actin polymerization and cell movement. Sequence analysis revealed 83% similarity with non-pathogenic N. gruberi and 38% similarity with Acanthamoeba castellanii. Nf-profilin was found to be associated with N. fowleri lysates but not with lysates from other amoebae, as shown by Western blot analysis. Immunofluorescence assays demonstrated that nf-profilin primarily localized to the cell membrane in N. fowleri cysts, while nf-actin localized to the cytoplasm, pseudopodia, and food-cup structures. Real-time RT-PCR indicated higher expression of the nf-profilin gene in cysts compared to trophozoites. In co-culture experiments with target cells, Nf-profilin was initially expressed in the cytoplasm of N. fowleri cysts and the morphology of cyst gradually transitioned to the trophozoite form. Concurrently, the expression of Nf-profilin protein decreased, while Nf-actin protein began to appear in the pseudopodia and food-cups of trophozoites. In conclusion, the nf-profilin and nf-actin genes exhibited complementary expression patterns based on the life stage of N. fowleri, indicating their critical roles in the survival and proliferation. This study emphasizes the significance of actin-binding proteins in understanding the infection and pathogenic mechanisms of N. fowleri.

Insights Into the Mechanism of Action of Chlorhexidine on Porphyromonas gingivalis

Chlorhexidine (CHX) remains the most effective antiseptic in periodontal therapy, multiple reports have identified ultrastructural antibacterial effects of CHX on oral bacteria, however, little is known about its molecular mechanism of action on Porphyromonas gingivalis, an important pathobiont directly associated with the pathogenesis of periodontitis. A standardized suspension of P. gingivalis ATCC 33277 was expose to 0.20% CHX for 1 min, then counting colony forming units (CFUs) were recovered to determine the percentage of microbial inhibition. Protein extract integrity of the bacterial cells exposed to CHX was evaluated on a one-dimension sodium dodecyl sulfate polyacrylamide gel electrophoresis (1D SDS-PAGE) gel. The identification of the proteins expressed by P. gingivalis after its exposure to CHX was carried out by mass spectrometry (LC-MS). Exposure of P. gingivalis for 1 min to 0.20% CHX resulted in a 93% reduction in bacterial viability, in addition to an increase of 2.9-fold in protein expression, with the Lys gingipain protein showing the greatest increase. Exposure to 0.20% CHX 1 min on P. gingivalis resulted in 93% reduction in bacterial viability, in addition to inducing changes in the bacterial proteome, with an increased expression of gingipains, the main virulence factor of P. gingivalis.

Enlightening the promising role of nanoparticle-based treatments against Naegleria fowleri-induced primary amoebic meningoencephalitis: A brain-eating disease

Naegleria fowleri, is the causative agent of Primary Amoebic Meningoencephalitis (PAM), a lethal acute brain inflammation with high mortality. The virulent and reproductively active trophozoite stage of N. fowleri migrates to central nervous system (CNS) by entering through nasal passage and causes severe neural infection, brain disease and inflammation with high mortality. In this review we present the current available information about N. fowleri, including its case reports, pathogenesis and the mechanism of host neuroinflammation associated with PAM. Various case reports reveal that the survival rate of patients with PAM is very low. Several anti-microbial, anti-parasitic and anti-inflammatory compounds such as doxycycline, amphotericin, acyclovir, miltefosine, ampicillin, ceftriaxone, azithromycin are widely used to treat PAM. Nanoparticles conjugated drug has now attracted better attention in dealing with free-living amoeba community. Conventional drugs are being conjugated with nanomaterials like gold (Au), sliver (Ag) etc. which have elicited better amoebicidal effect against N. fowleri than unconjugated drugs. This targeted strategy may prove helpful and possibly may reduce neural damage.

Analysis of virulence factors in extracellular vesicles secreted by Naegleria fowleri

Naegleria fowleri is the etiological agent of primary amebic meningoencephalitis (PAM), a rapidly progressive acute and fulminant infection that affects the central nervous system, particularly of children and young adults, which has a mortality rate greater than 95%, and its symptomatologic similarity with other meningitis caused by virus or bacteria makes it difficult to make a quick and timely diagnosis that prevents the progression of the infection. It is necessary to know the antigenic determinants as well as the pathogenicity mechanisms of this amoeba to implement strategies that allow for better antiamoebic therapeutic and diagnostic targets that directly impact the health sector. Therefore, the aim of this work was to analyze some virulence factors as part of extracellular vesicle (EV) cargo secreted by N. fowleri. The EV secretion to the extracellular medium was evaluated in trophozoites fixed and incubated with anti-N. fowleri antibody while molecular identification of EV cargo was performed by SDS-PAGE, Western blot, and RT-PCR. Our results showed that N. fowleri secretes a wide variety of vesicle sizes ranging from 0.2 to > 2 μm, and these EVs were recognized by antibodies anti-Naegleropore B, anti-19 kDa polypeptide band, anti-membrane protein Mp2CL5, anti-protease cathepsin B, and anti-actin. Furthermore, these vesicles were localized in the trophozoites cytoplasm or secreted into the extracellular medium. Specifically in relation to small vesicles, our purified exosomes were recognized by CD63 and Hsp70 markers, along with the previously mentioned proteins. RT-PCR analysis was made through the isolation of EVs from N. fowleri trophozoite culture by concentration, filtration, and ultracentrifugation. Interestingly, we obtained PCR products for Nfa1, NPB, Mp2CL5, and CatB genes as part of exosomes cargo. This suggests that the molecules identified in this work could play an important role in communication as well as in infectious processes caused by this amoeba. Therefore, the study and characterization of the pathogenicity mechanisms, as well as the virulence factors released by N. fowleri remains a key point to provide valuable information for the development of therapeutic treatments, vaccine design, or biomarkers for a timely diagnosis against infections caused by protozoa.

THE 72-KDA PROTEIN OF NAEGLERIA FOWLERI PLAYS AN IMPORTANT ROLE IN THE ADHESION OF TROPHOZOITES TO BALB/C MICE NASAL EPITHELIUM

Naegleria fowleri is a protozoan that causes primary amebic meningoencephalitis (PAM). The infection occurs when the trophozoites enter the nasal cavity, adhere to the nasal mucosa, invade the epithelium, and migrate until they reach the olfactory bulb. Like other pathogens, there is evidence that the adhesion of N. fowleri to host cells is an important factor in the process of cytopathogenicity and disease progression. However, the factors involved in the adhesion of the pathogen to the cells of the nasal epithelium have not been characterized. The objective of this study was to identify a protein on the surface of N. fowleri, which could act as adhesin to the mouse nasal epithelium in the PAM model. The interaction between proteins of extracts of N. fowleri and cells of the nasal epithelium of BALB/c mice was analyzed using overlay and Western blot assays. A 72-kDa band of N. fowleri interacted directly with epithelial cell proteins, this polypeptide band was purified and analyzed by mass spectrometry. Analysis revealed that polypeptide bands of 72 kDa contained peptides that matched the membrane protein, actin 1 and 2, and Hsp70. Moreover, the N. fowleri extracts resolved in 2D-SDS-PAGE showed that 72-kDa spot interacted with proteins of mouse epithelial cells, which include characteristics of the theoretical data of molecular weight and pH obtained in the analysis by mass spectrometry. Immunofluorescence tests showed that this protein is located on the surface of trophozoites and plays an important role in the adhesion of amoeba either in vitro or in vivo assays, suggesting that this protein contributes during the N. fowleri invasion and migration to the brain, causing primary amoebic meningoencephalitis.

Immunogens in Balamuthia mandrillaris: a proteomic exploration

Balamuthia mandrillaris is the causative agent of granulomatous amoebic encephalitis, a rare and often fatal infection affecting the central nervous system. The amoeba is isolated from diverse environmental sources and can cause severe infections in both immunocompromised and immunocompetent individuals. Given the limited understanding of B. mandrillaris, our research aimed to explore its protein profile, identifying potential immunogens crucial for early granulomatous amoebic encephalitis diagnosis. Cultures of B. mandrillaris and other amoebas were grown under axenic conditions, and total amoebic extracts were obtained. Proteomic analyses, including two-dimensional electrophoresis and mass spectrometry, were performed. A 50-kDa band showed a robust recognition of antibodies from immunized BALB/c mice; peptides contained in this band were matched with elongation factor-1 alpha, which emerged as a putative key immunogen. Besides, lectin blotting revealed the presence of glycoproteins in B. mandrillaris, and confocal microscopy demonstrated the focal distribution of the 50-kDa band throughout trophozoites. Cumulatively, these observations suggest the participation of the 50-kDa band in adhesion and recognition mechanisms. Thus, these collective findings demonstrate some protein characteristics of B. mandrillaris, opening avenues for understanding its pathogenicity and developing diagnostic and therapeutic strategies.

Two MP2CL5 Antigen Vaccines from Naegleria fowleri Stimulate the Immune Response against Meningitis in the BALB/c Model

Naegleria fowleri is an etiological agent that generates primary amoebic meningoencephalitis; unfortunately, no effective treatment or vaccine is available. The objective of this work was to determine the immunoprotective response of two vaccine antigens, as follows: (i) the polypeptide band of 19 kDa or (ii) a predicted immunogenic peptide from the membrane protein MP2CL5 (Smp145). Both antigens were administered intranasally in mice using cholera toxin (CT) as an adjuvant. The survival rate and immune response of immunized mice with both antigens and challenged with N. fowleri trophozoites were measured in the nose-associated lymphoid tissue (NALT) and nasal passages (NPs) by flow cytometry and enzyme-linked immunosorbent assay (ELISA). We also determined the immunolocalization of both antigens in N. fowleri trophozoites by confocal microscopy. Immunization with the polypeptide band of 19 kDa alone or coadministered with CT was able to confer 80% and 100% of protection, respectively. The immunization with both antigens (alone or coadministered with CT) showed an increase in T and B lymphocytes. In addition, there was an increase in the expression of integrin α4β1 and IgA in the nasal cavity of protected mice, and the IgA, IgG, and IgM levels were increased in serum and nasal washes. The immunolocalization of both antigens in N. fowleri trophozoites was observed in the plasma membrane, specifically in pseudopod-like structures. The MP2CL5 antigens evaluated in this work were capable of conferring protection which would lead us to consider them as potential candidates for vaccines against meningitis caused by N. fowleri.

Role of FcγRIII in the nasal cavity of BALB/c mice in the primary amebic meningoencephalitis protection model

Different mechanisms of the host immune response against the primary amebic meningoencephalitis (PAM) in the mouse protection model have been described. It has been proposed that antibodies opsonize Naegleria fowleri trophozoites; subsequently, the polymorphonuclear cells (PMNs) surround the trophozoites to avoid the infection. FcγRs activate signaling pathways of adapter proteins such as Syk and Hck on PMNs to promote different effector cell functions which are induced by the Fc portion of the antibody-antigen complexes. In this work, we analyzed the activation of PMNs, epithelial cells, and nasal passage cells via the expression of Syk and Hck genes. Our results showed an increment of the FcγRIII and IgG subclasses in the nasal cavity from immunized mice as well as Syk and Hck expression was increased, whereas in the in vitro assay, we observed that when the trophozoites of N. fowleri were opsonized with IgG anti-N. fowleri and interacted with PMN, the expression of Syk and Hck was also increased. We suggest that PMNs are activated via their FcγRIII, which leads to the elimination of the trophozoites in vitro, while in the nasal cavity, the adhesion and consequently infection are avoided.

Characterization of Extracellular Vesicles Secreted by a Clinical Isolate of Naegleria fowleri and Identification of Immunogenic Components within Their Protein Cargo

Extracellular vesicles (EVs) are small lipid vesicles released by both prokaryotic and eukaryotic cells, involved in intercellular communication, immunomodulation and pathogenesis. In this study, we performed a characterization of the EVs produced by trophozoites of a clinical isolate of the free-living amoeba Naegleria fowleri (N. fowleri). Size distribution, zeta potential, protein profile and protease activity were analyzed. Under our incubation conditions, EVs of different sizes were observed, with a predominant population ranging from 206 to 227 nm. SDS-PAGE revealed protein bands of 25 to 260 KDa. The presence of antigenic proteins was confirmed by Western blot, which evidenced strongest recognition by rat polyclonal antibodies raised against N. fowleri in the region close to 80 KDa and included peptidases, as revealed by zymography. Proteins in selected immunorecognized bands were further identified using nano-ESI-MS/MS. A preliminary proteomic profile of the EVs identified at least 184 proteins as part of the vesicles' cargo. Protease activity assays, in combination with the use of inhibitors, revealed the predominance of serine proteases. The present characterization uncovers the complexity of EVs produced by N. fowleri, suggesting their potential relevance in the release of virulence factors involved in pathogenicity. Owing to their cargo's diversity, further research on EVs could reveal new therapeutic targets or biomarkers for developing rapid and accurate diagnostic tools for lethal infections such as the one caused by this amoeba.

Primary Amoebic Meningoencephalitis by Naegleria fowleri: Pathogenesis and Treatments

Naegleria fowleri is a free-living amoeba (FLA) that is commonly known as the "brain-eating amoeba." This parasite can invade the central nervous system (CNS), causing an acute and fulminating infection known as primary amoebic meningoencephalitis (PAM). Even though PAM is characterized by low morbidity, it has shown a mortality rate of 98%, usually causing death in less than two weeks after the initial exposure. This review summarizes the most recent information about N. fowleri, its pathogenic molecular mechanisms, and the neuropathological processes implicated. Additionally, this review includes the main therapeutic strategies described in case reports and preclinical studies, including the possible use of immunomodulatory agents to decrease neurological damage.

Isolation and Identification of Naegleria Species in Irrigation Channels for Recreational Use in Mexicali Valley, Mexico

Members of the genus Naegleria are free-living amoebae that are widely distributed in water and soil environments. Moreover, Naegleria fowleri is a pathogenic amoeba species that causes a fatal disease in the central nervous system known as primary amoebic meningoencephalitis (PAM) in humans. Since most reported infections due to N. fowleri are reported in recreational waters worldwide, this study was aimed to describe the presence of these amoebic genus in Mexicali Valley irrigation channels of recreational use. A total of nine water samples were collected and processed by triplicate, in nine different sites of the Valley. After filtering and culturing the samples, plates were examined, and the observed amoebae were morphologically identified at the genus level. In addition, the pathogenicity of these amoebic isolates was checked, and molecular characterization was performed by PCR/sequencing. The results revealed the presence of Naegleria spp. in all the channels sampled. Finally, molecular identification confirmed the presence of five different species of Naegleria: N. fowleri, N. australiensis, N. gruberi, N. clarki and N. pagei. The presence of these protists, particularly N. fowleri, should be considered as a potential human health risk in the region.

Identification of Immunogenic Antigens of Naegleria fowleri Adjuvanted by Cholera Toxin

The intranasal administration of Naegleria fowleri lysates plus cholera toxin (CT) increases protection against N. fowleri meningoencephalitis in mice, suggesting that humoral immune response mediated by antibodies is crucial to induce protection against the infection. In the present study, we applied a protein analysis to detect and identify immunogenic antigens from N. fowleri, which might be responsible for such protection. A Western blot assay of N. fowleri polypeptides was performed using the serum and nasal washes from mice immunized with N. fowleri lysates, either alone or with CT after one, two, three, or four weekly immunizations and challenged with trophozoites of N. fowleri. Immunized mice with N. fowleri plus CT, after four doses, had the highest survival rate (100%). Nasal or sera IgA and IgG antibody response was progressively stronger as the number of immunizations was increased, and that response was mainly directed to 250, 100, 70, 50, 37, and 19 kDa polypeptide bands, especially in the third and fourth immunization. Peptides present in these immunogenic bands were matched by nano-LC–ESI-MSMS with different proteins, which could serve as candidates for a vaccine against N. fowleri infection.