Surface-expressed enolase contributes to the pathogenesis of clinical isolate SSU of Aeromonas hydrophila

Advances and Challenges in Aeromonas hydrophila Vaccine Development: Immunological Insights and Future Perspectives

Aeromonas hydrophila presents a significant threat to global aquaculture due to its ability to infect freshwater and marine fish species, leading to substantial economic losses. Effective mitigation methods are essential to address these challenges. Vaccination has emerged as a promising strategy to reduce A. hydrophila infections; however, it faces several obstacles, including variability in immune responses, pathogen diversity, and environmental factors affecting vaccine efficacy. To enhance vaccine performance, researchers focus on adjuvants to boost immune responses and develop multivalent vaccines targeting multiple A. hydrophila strains. Tailoring vaccines to specific environmental conditions and optimizing vaccination schedules can further address the challenges posed by pathogen diversity and variable immune responses. This review provides an in-depth analysis of the immunological hurdles associated with A. hydrophila vaccine development. Current vaccine types-live attenuated, inactivated, subunit, recombinant, and DNA-exhibit diverse mechanisms for stimulating innate and adaptive immunity, with varying levels of success. Key focus areas include the potential of advanced adjuvants and nanoparticle delivery systems to overcome existing barriers. The review also highlights the importance of understanding host-pathogen interactions in guiding the development of more targeted and effective immune responses in fish. Complementary approaches, such as immunostimulants, probiotics, and plant-based extracts, are explored as adjuncts to vaccination in aquaculture health management. Despite notable progress, challenges remain in translating laboratory innovations into scalable, cost-effective solutions for aquaculture. Future directions emphasize the integration of advanced genomic and proteomic tools to identify novel antigen candidates and the need for industry-wide collaborations to standardize vaccine production and delivery. Addressing these challenges can unlock the potential of innovative vaccine technologies to safeguard fish health and promote sustainable aquaculture practices globally.

Clinical Presentation, Antimicrobial Resistance, and Treatment Outcomes of Aeromonas Human Infections: A 14-Year Retrospective Study and Comparative Genomics of 2 Isolates From Fatal Cases

BACKGROUND

Aeromonas virulence may not be entirely dependent on the host's immune status. Pathophysiologic determinants of disease progression and severity remain unclear.

METHODS

One hundred five patients with Aeromonas infections and 112 isolates were identified, their clinical presentations and outcomes were analyzed, and their antimicrobial resistance (AMR) patterns were assessed. Two isolates (A and B) from fatal cases of Aeromonas dhakensis bacteremia were characterized using whole-genome sequencing. Virulence factor- and AMR-encoding genes from these isolates were compared with a well-characterized diarrheal isolate A. dhakensis SSU and environmental isolate Aeromonas hydrophila American Type Culture Collection_7966T.

RESULTS

Skin and soft tissue infections, traumatic wound infections, sepsis, burns, and intraabdominal infections were common. Diabetes, malignancy, and cirrhosis were frequent comorbidities. Male sex, age ≥ 65 years, hospitalization, burns, and intensive care admission were associated with complicated disease. High rates of AMR to carbapenems and piperacillin-tazobactam were found. Treatment failure was observed in 25.7% of cases. Septic shock and hospital-acquired infections were predictors of treatment failure. All 4 isolates harbored assorted broad-spectrum AMR genes including blaOXA, ampC, cphA, and efflux pumps. Only clinical isolates possessed both polar and lateral flagellar genes, genes for various surface adhesion proteins, type 3 and 6 secretion systems and their effectors, and toxin genes, including exotoxin A. Both isolates A and B were resistant to colistin and harbored the mobile colistin resistance-3 (mcr-3) gene.

CONCLUSIONS

Empirical therapy tailored to local antibiograms may facilitate favorable outcomes, while advanced diagnostic methods may aid in identifying correct Aeromonas spp. of significant clinical importance.

An alternative vaccine target for bovine Anaplasmosis based on enolase, a moonlighting protein

The discovery of new targets for preventing bovine anaplasmosis has moved away from focusing on proteins that have already been extensively studied in Anaplasma marginale, including the Major Surface Proteins, Outer Membrane Proteins, and Type IV Secretion System proteins. An alternative is moonlighting or multifunctional proteins, capable of performing various biological functions within various cellular compartments. There are several reports on the role of moonlighting proteins as virulence factors in various microorganisms. Moreover, it is known that about 25% of all moonlighting is involved in the virulence of pathogens. In this work, for the first time, we present the identification of three enolase proteins (AmEno01, AmEno15, and AmEno31) in the genome of Mexican strains of A. marginale. Using bioinformatics tools, we predicted the catalytic domains, enolase signature, and amino acids binding magnesium ion of the catalytic domain and performed a phylogenetic reconstruction. In addition, by molecular docking analysis, we found that AmEno01 would bind to erythrocyte proteins spectrin, ankyrin, and stomatin. This adhesion function has been reported for enolases from other pathogens. It is considered a promising target since blocking this function would impede the fundamental adhesion process that facilitates the infection of erythrocytes. Additionally, molecular docking predicts that AmEno01 could bind to extracellular matrix protein fibronectin, which would be significant if we consider that some proteins with fibronectin domains are localized in tick gut cells and used as an adhesion strategy to gather bacteria before traveling to salivary glands. Derived from the molecular docking analysis of AmEno01, we hypothesized that enolases could be proteins driven by the pathogen and redirected at the expense of the pathogen's needs.

The Recruitment and Activation of Plasminogen by Bacteria-The Involvement in Chronic Infection Development

The development of infections caused by pathogenic bacteria is largely related to the specific properties of the bacterial cell surface and extracellular hydrolytic activity. Furthermore, a significant role of hijacking of host proteolytic cascades by pathogens during invasion should not be disregarded during consideration of the mechanisms of bacterial virulence. This is the key factor for the pathogen evasion of the host immune response, tissue damage, and pathogen invasiveness at secondary infection sites after initial penetration through tissue barriers. In this review, the mechanisms of bacterial impact on host plasminogen-the precursor of the important plasma serine proteinase, plasmin-are characterized, principally focusing on cell surface exposition of various proteins, responsible for binding of this host (pro)enzyme and its activators or inhibitors, as well as the fibrinolytic system activation tactics exploited by different bacterial species, not only pathogenic, but also selected harmless residents of the human microbiome. Additionally, the involvement of bacterial factors that modulate the process of plasminogen activation and fibrinolysis during periodontitis is also described, providing a remarkable example of a dual use of this host system in the development of chronic diseases.

Non-metabolic role of alpha-enolase in virus replication

Viruses are extremely complex and highly evolving microorganisms; thus, it is difficult to analyse them in detail. The virion is believed to contain all the essential components required from its entry to the establishment of a successful infection in a susceptible host cell. Hence, the virion composition is the principal source for its transmissibility and immunogenicity. A virus is completely dependent on a host cell for its replication and progeny production. Occasionally, they recruit and package host proteins into mature virion. These incorporated host proteins are believed to play crucial roles in the subsequent infection, although the significance and the molecular mechanism regulated are poorly understood. One such host protein which is hijacked by several viruses is the glycolytic enzyme, Enolase (Eno-1) and is also packaged into mature virion of several viruses. This enzyme exhibits a highly flexible nature of functions, ranging from metabolic to several non-metabolic activities. All the glycolytic enzymes are known to be moonlighting proteins including enolase. The non-metabolic functions of this moonlighting protein are also highly diverse with respect to its cellular localization. Although very little is known about the virological significance of this enzyme, several of its non-metabolic functions have been observed to influence the virus replication cycle in infected cells. In this review, we have attempted to provide a comprehensive picture of the non-metabolic role of Eno-1, its significance in the virus replication cycle and to stimulate interest around its scope as a therapeutic target for treating viral pathologies.

Bacteriophage protein PEIP is a potent Bacillus subtilis enolase inhibitor

Enolase is a highly conserved enzyme that presents in all organisms capable of glycolysis or fermentation. Its immediate product phosphoenolpyruvate is essential for other important processes like peptidoglycan synthesis and the phosphotransferase system in bacteria. Therefore, enolase inhibitors are of great interest. Here, we report that Gp60, a phage-encoded enolase inhibitor protein (PEIP) of bacteriophage SPO1 for Bacillus subtilis, is an enolase inhibitor. PEIP-expressing bacteria exhibit growth attenuation, thinner cell walls, and safranin color in Gram staining owing to impaired peptidoglycan synthesis. We solve the structure of PEIP-enolase tetramer and show that PEIP disassembles enolase by disrupting the basic dimer unit. The structure reveals that PEIP does not compete for substrate binding but induces a cascade of conformational changes that limit accessibility to the enolase catalytic site. This phage-inspired disassembly of enolase represents an alternative strategy for the development of anti-microbial drugs.

Enolase of Staphylococcus lugdunensis Is a Surface-Exposed Moonlighting Protein That Binds to Extracellular Matrix and the Plasminogen/Plasmin System

The coagulase-negative staphylococcal (CoNS) species Staphylococcus lugdunensis is unique in causing serious infections in humans that resemble those of Staphylococcus aureus rather than those of other CoNS species. The colonization and invasion of host tissue presupposes the presence of adherence factors, but only a few proteins mediating adhesion of S. lugdunensis to biotic surfaces are known yet. Here, we report on the functionality of the S. lugdunensis enolase (SlEno), which performs two distinct roles, first, as the metabolic enzyme of the glycolysis, and second, as an adherence factor to the extracellular matrix (ECM) of cells. Phylogenetic analyses of the SlEno confirmed their high conservation to enolases of other species and revealed a closer relationship to Staphylococcus epidermidis than to S. aureus. Using matrix-assisted laser desorption/ionization time of flight mass spectrometry and Western blot experiments, we identified SlEno to be located in the cytoplasm as well as on the cell surface of S. lugdunensis. Recombinantly generated and surface-associated SlEno showed the usual enolase activity by catalyzing the conversion of 2-phosphoglycerate to phosphoenolpyruvate but, in addition, also displayed strong binding to immobilized laminin, fibronectin, fibrinogen, and collagen type IV in a dose-dependent manner. We also showed a strong binding of SlEno to plasminogen (Plg) and observed a tissue plasminogen activator (tPA)-dependent conversion of Plg to plasmin (Pln) whereby the Plg activation significantly increased in the presence of SlEno. This interaction might be dependent on lysines of the SlEno protein as binding to Plg was inhibited by ε-aminocaproic acid. Furthermore, the enhanced activation of the Plg/Pln system by SlEno enabled S. lugdunensis to migrate through a fibrin matrix. This migration was about 10-fold higher than without exogenously added SlEno. Finally, we observed a significantly higher clearance of S. lugdunensis by freshly prepared granulocytes and in the presence of anti-SlEno antibodies. In conclusion, these data demonstrate for the first time a moonlighting function of the S. lugdunensis enolase, which is an underrated virulence factor for colonization and invasion of tissues. Hence, SlEno might be a potential vaccine candidate to prevent severe infections caused by this pathogen.

A journey through the Corynebacterium pseudotuberculosis proteome promotes insights into its functional genome

Background

Corynebacterium pseudotuberculosis is a Gram-positive facultative intracellular pathogen and the etiologic agent of illnesses like caseous lymphadenitis in small ruminants, mastitis in dairy cattle, ulcerative lymphangitis in equines, and oedematous skin disease in buffalos. With the growing advance in high-throughput technologies, genomic studies have been carried out to explore the molecular basis of its virulence and pathogenicity. However, data large-scale functional genomics studies are necessary to complement genomics data and better understating the molecular basis of a given organism. Here we summarize, MS-based proteomics techniques and bioinformatics tools incorporated in genomic functional studies of C. pseudotuberculosis to discover the different patterns of protein modulation under distinct environmental conditions, and antigenic and drugs targets.

Methodology

In this study we performed an extensive search in Web of Science of original and relevant articles related to methods, strategy, technology, approaches, and bioinformatics tools focused on the functional study of the genome of C. pseudotuberculosis at the protein level.

Results

Here, we highlight the use of proteomics for understating several aspects of the physiology and pathogenesis of C. pseudotuberculosis at the protein level. The implementation and use of protocols, strategies, and proteomics approach to characterize the different subcellular fractions of the proteome of this pathogen. In addition, we have discussed the immunoproteomics, immunoinformatics and genetic tools employed to identify targets for immunoassays, drugs, and vaccines against C. pseudotuberculosis infection.

Conclusion

In this review, we showed that the combination of proteomics and bioinformatics studies is a suitable strategy to elucidate the functional aspects of the C. pseudotuberculosis genome. Together, all information generated from these proteomics studies allowed expanding our knowledge about factors related to the pathophysiology of this pathogen.

Klebsiella pneumoniae enolase-like membrane protein interacts with human plasminogen

Many models assessing the risk of sepsis utilize the knowledge of the constituents of the plasminogen system, as it is proven that some species of bacteria can activate plasminogen, as a result of interactions with bacterial outer membrane proteins. However, much is yet to be discovered about this interaction since there is little information regarding some bacterial species. This study is aimed to check if Klebsiella pneumoniae, one of the major factors of nosocomial pneumonia and a factor for severe sepsis, has the ability to bind to human plasminogen. The strain used in this study, PCM 2713, acted as a typical representative of the species. With use of various methods, including: electron microscopy, 2-dimensional electrophoresis, immunoblotting and peptide fragmentation fingerprinting, it is shown that Klebsiella pneumoniae binds to human plasminogen, among others, due to plasminogen-bacterial enolase-like protein interaction, occurring on the outer membrane of the bacterium. Moreover, the study reveals, that other proteins, such as: phosphoglucomutase, and phosphoenolpyruvate carboxykinase act as putative plasminogen-binding factors. These information may virtually act as a foundation for future studies investigating: the: pathogenicity of Klebsiella pneumoniae and means for prevention from the outcomes of Klebsiella-derived sepsis.

Moonlighting Proteins: The Case of the Hexokinases

Moonlighting proteins are defined as proteins with two or more functions that are unrelated and independent to each other, so that inactivation of one of them should not affect the second one and vice versa. Intriguingly, all the glycolytic enzymes are described as moonlighting proteins in some organisms. Hexokinase (HXK) is a critical enzyme in the glycolytic pathway and displays a wide range of functions in different organisms such as fungi, parasites, mammals, and plants. This review discusses HXKs moonlighting functions in depth since they have a profound impact on the responses to nutritional, environmental, and disease challenges. HXKs’ activities can be as diverse as performing metabolic activities, as a gene repressor complexing with other proteins, as protein kinase, as immune receptor and regulating processes like autophagy, programmed cell death or immune system responses. However, most of those functions are particular for some organisms while the most common moonlighting HXK function in several kingdoms is being a glucose sensor. In this review, we also analyze how different regulation mechanisms cause HXK to change its subcellular localization, oligomeric or conformational state, the response to substrate and product concentration, and its interactions with membrane, proteins, or RNA, all of which might impact the HXK moonlighting functions.

The Role of Metabolic Enzymes in the Regulation of Inflammation

Immune cells undergo dramatic metabolic reprogramming in response to external stimuli. These metabolic pathways, long considered as simple housekeeping functions, are increasingly understood to critically regulate the immune response, determining the activation, differentiation, and downstream effector functions of both lymphoid and myeloid cells. Within the complex metabolic networks associated with immune activation, several enzymes play key roles in regulating inflammation and represent potential therapeutic targets in human disease. In some cases, these enzymes control flux through pathways required to meet specific energetic or metabolic demands of the immune response. In other cases, key enzymes control the concentrations of immunoactive metabolites with direct roles in signaling. Finally, and perhaps most interestingly, several metabolic enzymes have evolved moonlighting functions, with roles in the immune response that are entirely independent of their conventional enzyme activities. Here, we review key metabolic enzymes that critically regulate inflammation, highlighting mechanistic insights and opportunities for clinical intervention.

Structural Insights into the Interactions of Candidal Enolase with Human Vitronectin, Fibronectin and Plasminogen

Significant amounts of enolase—a cytosolic enzyme involved in the glycolysis pathway—are exposed on the cell surface of Candida yeast. It has been hypothesized that this exposed enolase form contributes to infection-related phenomena such as fungal adhesion to human tissues, and the activation of fibrinolysis and extracellular matrix degradation. The aim of the present study was to characterize, in structural terms, the protein-protein interactions underlying these moonlighting functions of enolase. The tight binding of human vitronectin, fibronectin and plasminogen by purified C. albicans and C. tropicalis enolases was quantitatively analyzed by surface plasmon resonance measurements, and the dissociation constants of the formed complexes were determined to be in the 10⁻⁷–10⁻⁸ M range. In contrast, the binding of human proteins by the S.cerevisiae enzyme was much weaker. The chemical cross-linking method was used to map the sites on enolase molecules that come into direct contact with human proteins. An internal motif ₂₃₅DKAGYKGKVGIAMDVASSEFYKDGK₂₅₉ in C. albicans enolase was suggested to contribute to the binding of all three human proteins tested. Models for these interactions were developed and revealed the sites on the enolase molecule that bind human proteins, extensively overlap for these ligands, and are well-separated from the catalytic activity center.

Population Genomic Analysis of Mycoplasma bovis Elucidates Geographical Variations and Genes associated with Host-Types

Among more than twenty species belonging to the class Mollecutes, Mycoplasma bovis is the most common cause of bovine mycoplasmosis in North America and Europe. Bovine mycoplasmosis causes significant economic loss in the cattle industry. The number of M. bovis positive herds recently has increased in North America and Europe. Since antibiotic treatment is ineffective and no efficient vaccine is available, M. bovis induced mycoplasmosis is primarily controlled by herd management measures such as the restriction of moving infected animals out of the herds and culling of infected or shedders of M. bovis. To better understand the population structure and genomic factors that may contribute to its transmission, we sequenced 147 M. bovis strains isolated from four different countries viz. USA (n = 121), Canada (n = 22), Israel (n = 3) and Lithuania (n = 1). All except two of the isolates (KRB1 and KRB8) were isolated from two host types i.e., bovine (n = 75) and bison (n = 70). We performed a large-scale comparative analysis of M. bovis genomes by integrating 103 publicly available genomes and our dataset (250 total genomes). Whole genome single nucleotide polymorphism (SNP) based phylogeny using M.agalactiae as an outgroup revealed that M. bovis population structure is composed of five different clades. USA isolates showed a high degree of genomic divergence in comparison to the Australian isolates. Based on host of origin, all the isolates in clade IV was of bovine origin, whereas majority of the isolates in clades III and V was of bison origin. Our comparative genome analysis also revealed that M. bovis has an open pangenome with a large breadth of unexplored diversity of genes. The function based analysis of autogenous vaccine candidates (n = 10) included in this study revealed that their functional diversity does not span the genomic diversity observed in all five clades identified in this study. Our study also found that M. bovis genome harbors a large number of IS elements and their number increases significantly (p = 7.8 × 10⁻⁶) as the genome size increases. Collectively, the genome data and the whole genome-based population analysis in this study may help to develop better understanding of M. bovis induced mycoplasmosis in cattle.

Pathogenic profile and cytotoxic activity of Aeromonas spp. isolated from Pectinatella magnifica and surrounding water in the South Bohemian aquaculture region

Pectinatella magnifica is an invasive freshwater bryozoan that has expanded in many localities worldwide, including fishing areas. It contains microbial communities, predominantly consisting of Aeromonas bacteria that are frequently associated with fish infections. The objective of this study was to investigate the potential pathogenicity of Aeromonas spp. associated with P. magnifica and evaluate the health risks for fish. Aeromonas strains were isolated from P. magnifica (101 strains) and from surrounding water (29 strains) in the South Bohemian region and investigated for the presence of 14 virulence-associated genes using PCR. We demonstrated high prevalence of phospholipase GCAT, polar flagellin, enolase, DNAse, aerolysin/cytotoxic enterotoxin, serine protease and heat-stable cytotonic enterotoxin-coding genes. Further, all twelve isolates that were analysed for cytotoxicity against intestinal epithelial cells were found to be cytotoxic. Six of the isolates were also tested as co-cultures composed of pairs. Enhanced cytotoxicity was observed when the pair was composed of strains from different species. In conclusion, P. magnifica is colonized by Aeromonas strains that have a relatively high prevalence of virulence-associated genes and the ability to provoke disease. Results also suggest a possibly increased risk arising from mixed infections.

Moonlighting Proteins in the Fuzzy Logic of Cellular Metabolism

The numerous interconnected biochemical pathways that make up the metabolism of a living cell comprise a fuzzy logic system because of its high level of complexity and our inability to fully understand, predict, and model the many activities, how they interact, and their regulation. Each cell contains thousands of proteins with changing levels of expression, levels of activity, and patterns of interactions. Adding more layers of complexity is the number of proteins that have multiple functions. Moonlighting proteins include a wide variety of proteins where two or more functions are performed by one polypeptide chain. In this article, we discuss examples of proteins with variable functions that contribute to the fuzziness of cellular metabolism.

Analysis of virulence and immunogenic factors in Aeromonas hydrophila: Towards the development of live vaccines

Aeromonas hydrophila, a bacterium that is widespread in aquatic environments, is responsible for causing haemorrhagic disease in both aquatic and terrestrial species. With the purpose of developing a live vaccine, herein we have investigated nine strains of A. hydrophila (Ah-01 to Ah-09) isolated from diseased fish. A study of virulence factors that contribute to pathogenicity and immunogenicity in the host Cyprinus carpio suggests that the presence of β-hly, act and fla genes contribute to pathogenesis: strains Ah-01, Ah-02 and Ah-03 (β-hly⁺ /act⁺ /fla⁺ genotype) were highly pathogenic to C. carpio, whereas Ah-05 and Ah-06 (β-hly^- /act^- /fla^- genotype) showed weak pathogenicity. Accordingly, Ah-02 and Ah-03 were selected to prepare inactivated vaccines, whereas Ah-05 and Ah-06 were chosen as live vaccines. Ah-06 live vaccine was found to have the best protective efficacy, with a protective rate of about 85%, whereas rates of other vaccines were significantly lower, in the range 37%-59%. In addition, DNA vaccines based on genes altA, aha and omp showed immune protection rates of 25%, 37.5% and 75%, respectively. Our data demonstrate that the β-hly^- /act^- /fla^- /altA⁺ /aha⁺ /omp⁺ genotype has weak pathogenicity and high immunogenicity, and provide a simple and effective way to screen for live A. hydrophila vaccines.

α-Enolase as a novel vaccine candidate against Streptococcus dysgalactiae infection in cobia (Rachycentron canadum L.)

Streptococcus dysgalactiae is an important pathogenic bacterium that has caused economic loss for the cobia industry in Taiwan, ROC. This study presents a highly effective subunit vaccine composed of a moonlight protein, α-enolase, for the prevention of S. dysgalactiae infection. First, α-enolase was cloned, transformed, and expressed in E. coli for production of recombinant protein. Then, the protective efficacies of α-enolase recombinant protein were evaluated in combination with either a pro-inflammatory cytokine, TNF-α, or an oil adjuvant, ISA 763 AVG. The results showed that the combination of α-enolase and ISA 763 AVG was highly protective (RPS = 88.89%), while a negative effect was found in the group immunised with α-enolase adjuvanted with TNF-α (RPS = 22.22%). A further study was conducted with double dose of ISA 763 AVG, which led to an increased RPS value of 97.37%. Moreover, immunised cobia exhibited significantly greater lysozyme activity, antibody responses, and expression of certain immune-related genes post-challenge. Altogether, our results demonstrated that a combination of α-enolase recombinant protein with ISA 763 AVG adjuvant is a promising vaccine that can be employed for protection of cobia against S. dysgalactiae infection.

An Update on the Genus Aeromonas: Taxonomy, Epidemiology, and Pathogenicity

The genus Aeromonas belongs to the Aeromonadaceae family and comprises a group of Gram-negative bacteria widely distributed in aquatic environments, with some species able to cause disease in humans, fish, and other aquatic animals. However, bacteria of this genus are isolated from many other habitats, environments, and food products. The taxonomy of this genus is complex when phenotypic identification methods are used because such methods might not correctly identify all the species. On the other hand, molecular methods have proven very reliable, such as using the sequences of concatenated housekeeping genes like gyrB and rpoD or comparing the genomes with the type strains using a genomic index, such as the average nucleotide identity (ANI) or in silico DNA–DNA hybridization (isDDH). So far, 36 species have been described in the genus Aeromonas of which at least 19 are considered emerging pathogens to humans, causing a broad spectrum of infections. Having said that, when classifying 1852 strains that have been reported in various recent clinical cases, 95.4% were identified as only four species: Aeromonas caviae (37.26%), Aeromonas dhakensis (23.49%), Aeromonas veronii (21.54%), and Aeromonas hydrophila (13.07%). Since aeromonads were first associated with human disease, gastroenteritis, bacteremia, and wound infections have dominated. The literature shows that the pathogenic potential of Aeromonas is considered multifactorial and the presence of several virulence factors allows these bacteria to adhere, invade, and destroy the host cells, overcoming the immune host response. Based on current information about the ecology, epidemiology, and pathogenicity of the genus Aeromonas, we should assume that the infections these bacteria produce will remain a great health problem in the future. The ubiquitous distribution of these bacteria and the increasing elderly population, to whom these bacteria are an opportunistic pathogen, will facilitate this problem. In addition, using data from outbreak studies, it has been recognized that in cases of diarrhea, the infective dose of Aeromonas is relatively low. These poorly known bacteria should therefore be considered similarly as enteropathogens like Salmonella and Campylobacter.

[Clinical features and laboratory data analysis of Aeromonas bacteremia with hematological diseases]

Objective: To investigate the clinical and laboratory features of Aeromonas bacteremia in patients with hematological diseases, and provide evidence for the prevention and treatment of Aeromonas infection. Methods: A retrospective study of patients with bloodstream infection of Aeromonas in our hospital from January 2014 to December 2018 was carried out. The clinical characteristics, antimicrobial susceptibility, infection seasons, antimicrobial therapy and evolution were analyzed. Results: A total of 42 patients with hematological diseases had Aeromonas bloodstream infection within 5 years. Among them, 39 cases (92.9%) of bloodstream infection occurred in the stage of neutropenia. The median time of fever was 4 (1-27) d, 22 (52.4%) patients only had fever, 6 (14.3%) with gastrointestinal symptoms (abdominal pain, diarrhea, nausea, upper gastrointestinal bleeding) , 8 (19.0%) with pulmonary infection, 13 (31.0%) with skin and soft tissue infections. Seven patients (16.7%) died with skin and soft tissue infection. The resistance of Aeromonas to carbapenems was 68.3%-70.7%, while the resistance rate to cephalosporins, quinolones and aminoglycosides were less than 10%. Conclusions: Aeromonas bacteremia in patients with hematological diseases mainly occur in the neutropenia stage, usually with symptom like fever. The mortality is increased when accompanied by skin and soft tissue infection. Antibiotic use should be based on susceptibility results, and avoid the use of carbapenems.

Elevada frequência de Aeromonas spp. e genes de virulência em cultivos de tilápia-do-nilo (Oreochromis niloticus) em tanques-rede, na região semiárida de Pernambuco, Brasil

RESUMO Objetivou-se avaliar a ocorrência de Aeromonas spp. em peixes e amostras de água na região semiárida de Pernambuco e avaliar a frequência de aerolissina (aerA), enterotoxina citotóxica (act), enterotoxina citotônica (alt) e serina protease (ahp) nesses isolados. Foram analisados 70 peixes vivos e oito mortos com sinais clínicos de aeromoniose e 16 amostras de água. Aeromonas spp. foram identificadas por análises microbiológicas (provas bioquímicas) e molecular, usando-se primers específicos para a região 16S rRNA, e a distribuição dos quatro fatores de virulência (aerA, alt, act e ahp) foi investigada por ensaio de PCR. Cento e cinquenta e cinco (84,7%) isolados foram confirmados como Aeromonas spp. na análise molecular. Os genes de virulência mais frequentes foram act (53,55%) e aerA (51,61%). De acordo com o tipo de amostra, observou-se maior frequência do gene aerA (87,5% P=0,0474) em isolados de peixes mortos e a menor frequência do gene act (47,73% P=0,0002) em peixes vivos. Este estudo demonstrou a presença de aeromoniose no cultivo de tilápias em tanques-rede, nos municípios de Jatobá e Petrolândia, na região semiárida de Pernambuco. A detecção de aerA, act e alt pode ser utilizada na tipagem de virulência de Aeromonas spp.

Identity and virulence properties of Aeromonas isolates from healthy Northern snakehead (Channa argus) in China

Members of the genus Aeromonas are opportunistic pathogen of a variety of aquatic animals that exhibits multidrug resistance, phenotypes, virulence genes and virulence. The present study described the species distribution and the potential pathogenicity of Aeromonas isolated from healthy Northern snakehead (Channa argus) in China. Molecular identification revealed that A. veronii biovar veronii (69/167; 41·3%) and A. hydrophila (41/167; 24·6%) were the most common species found in Northern snakehead intestine based on sequencing of the 16S rRNA gene and DNA gyrase subunit B protein. The distribution of seven virulence factors including aer (84·4%), act (80·8%), ser (40·1%), Aha (27·5%), lip (23·4%), exu (15·0%) and LuxS (12·6%) were determined exclusively in Aeromonas isolates. All the seven virulence genes were present in 9·6% (16/167), among which 11 strains were identified as A. veronii biovar veronii. For the strains harbouring seven virulence genes, the 50% lethal doses (LD₅₀ ) of isolates were lower compared to the isolates carrying two virulence genes. The challenge tests revealed that isolate W31 had the lowest lethal dose, causing 50% mortality at 4·5 × 10³ colony-forming units (CFU) per ml. Furthermore, histopathology of Northern snakehead infected with Aeromonas strains showed necrosis and congestion in liver, spleen and kidney and also damage to the intestine. This study confirms that the Aeromonas strains isolated from healthy Northern snakehead may be a cause of concern for public health. SIGNIFICANCE AND IMPACT OF THE STUDY: Aeromonas species are widely distributed in aquatic environments and have considerable virulence potential. The aim of this study was to identify Aeromonas strains isolated from healthy Northern snakehead, and to investigate if Aeromonas species isolated from healthy fish potential pathogenicity with special reference to virulence and epidemiology studies.

Bacteriological, Clinical and Virulence Aspects of Aeromonas-associated Diseases in Humans

Aeromonads have been isolated from varied environmental sources such as polluted and drinking water, as well as from tissues and body fluids of cold and warm-blooded animals. A phenotypically and genotypically heterogenous bacteria, aeromonads can be successfully identified by ribotyping and/or by analysing gyrB gene sequence, apart from classical biochemical characterization. Aeromonads are known to cause scepticemia in aquatic organisms, gastroenteritis and extraintestinal diseases such as scepticemia, skin, eye, wound and respiratory tract infections in humans. Several virulence and antibiotic resistance genes have been identified and isolated from this group, which if present in their mobile genetic elements, may be horizontally transferred to other naive environmental bacteria posing threat to the society. The extensive and indiscriminate use of antibiotics has given rise to many resistant varieties of bacteria. Multidrug resistance genes, such as NDM1, have been identified in this group of bacteria which is of serious health concern. Therefore, it is important to understand how antibiotic resistance develops and spreads in order to undertake preventive measures. It is also necessary to search and map putative virulence genes of Aeromonas for fighting the diseases caused by them. This review encompasses current knowledge of bacteriological, environmental, clinical and virulence aspects of the Aeromonas group and related diseases in humans and other animals of human concern.

Exploring the Potential Role of Moonlighting Function of the Surface-Associated Proteins From Mycobacterium bovis BCG Moreau and Pasteur by Comparative Proteomic

Surface-associated proteins from Mycobacterium bovis BCG Moreau RDJ are important components of the live Brazilian vaccine against tuberculosis. They are important targets during initial BCG vaccine stimulation and modulation of the host's immune response, especially in the bacterial-host interaction. These proteins might also be involved in cellular communication, chemical response to the environment, pathogenesis processes through mobility, colonization, and adherence to the host cell, therefore performing multiple functions. In this study, the proteomic profile of the surface-associated proteins from M. bovis BCG Moreau was compared to the BCG Pasteur reference strain. The methodology used was 2DE gel electrophoresis combined with mass spectrometry techniques (MALDI-TOF/TOF), leading to the identification of 115 proteins. Of these, 24 proteins showed differential expression between the two BCG strains. Furthermore, 27 proteins previously described as displaying moonlighting function were identified, 8 of these proteins showed variation in abundance comparing BCG Moreau to Pasteur and 2 of them presented two different domain hits. Moonlighting proteins are multifunctional proteins in which two or more biological functions are fulfilled by a single polypeptide chain. Therefore, the identification of such proteins with moonlighting predicted functions can contribute to a better understanding of the molecular mechanisms unleashed by live BCG Moreau RDJ vaccine components.

When Place Matters: Shuttling of Enolase-1 Across Cellular Compartments

Enolase is a glycolytic enzyme, which catalyzes the inter-conversion of 2-phosphoglycerate to phosphoenolpyruvate. Altered expression of this enzyme is frequently observed in cancer and accounts for the Warburg effect, an adaptive response of tumor cells to hypoxia. In addition to its catalytic function, ENO-1 exhibits other activities, which strongly depend on its cellular and extracellular localization. For example, the association of ENO-1 with mitochondria membrane was found to be important for the stability of the mitochondrial membrane, and ENO-1 sequestration on the cell surface was crucial for plasmin-mediated pericellular proteolysis. The latter activity of ENO-1 enables many pathogens but also immune and cancer cells to invade the tissue, leading further to infection, inflammation or metastasis formation. The ability of ENO-1 to conduct so many diverse processes is reflected by its contribution to a high number of pathologies, including type 2 diabetes, cardiovascular hypertrophy, fungal and bacterial infections, cancer, systemic lupus erythematosus, hepatic fibrosis, Alzheimer's disease, rheumatoid arthritis, and systemic sclerosis. These unexpected non-catalytic functions of ENO-1 and their contributions to diseases are the subjects of this review.

Transcriptome analysis of Burkholderia pseudomallei SCV reveals an association with virulence, stress resistance and intracellular persistence

Differences in expression of potential virulence and survival genes were associated with B. pseudomallei colony morphology variants. Microarray was used to investigate B. pseudomallei transcriptome alterations among the wild type and small colony variant (SCV) pre- and post-exposed to A549 cells. SCV pre- and post-exposed have lower metabolic requirements and consume lesser energy than the wild type pre- and post-exposed to A549. However, both the wild type and SCV limit their metabolic activities post- infection of A549 cells and this is indicated by the down-regulation of genes implicated in the metabolism of amino acids, carbohydrate, lipid, and other amino acids. Many well-known virulence and survival factors, including T3SS, fimbriae, capsular polysaccharides and stress response were up-regulated in both the wild type and SCV pre- and post-exposed to A549 cells. Microarray analysis demonstrated essential differences in bacterial response associated with virulence and survival pre- and post-exposed to A549 cells.

Protein moonlighting: what is it, and why is it important?

Members of the GroEL/HSP60 protein family have been studied for many years because of their critical roles as ATP-dependent molecular chaperones, so it might come as a surprise that some have important functions in ATP-poor conditions, for example, when secreted outside the cell. At least some members of each of the HSP10, HSP70, HSP90, HSP100 and HSP110 heat shock protein families are also 'moonlighting proteins'. Moonlighting proteins exhibit more than one physiologically relevant biochemical or biophysical function within one polypeptide chain. In this class of multifunctional proteins, the multiple functions are not due to gene fusions or multiple proteolytic fragments. Several hundred moonlighting proteins have been identified, and they include a diverse set of proteins with a large variety of functions. Some participate in multiple biochemical processes by using an active site pocket for catalysis and a different part of the protein's surface to interact with other proteins. Moonlighting proteins play a central role in many diseases, and the development of novel treatments would be aided by more information addressing current questions, for example, how some are targeted to multiple cellular locations and how a single function can be targeted by therapeutics without targeting a function not involved in disease.This article is part of the theme issue 'Heat shock proteins as modulators and therapeutic targets of chronic disease: an integrated perspective'.

Intracellular proteins moonlighting as bacterial adhesion factors

Pathogenic and commensal, or probiotic, bacteria employ adhesins on the cell surface to attach to and interact with the host. Dozens of the adhesins that play key roles in binding to host cells or extracellular matrix were originally identified as intracellular chaperones or enzymes in glycolysis or other central metabolic pathways. Proteins that have two very different functions, often in two different subcellular locations, are referred to as moonlighting proteins. The intracellular/surface moonlighting proteins do not contain signal sequences for secretion or known sequence motifs for binding to the cell surface, so in most cases is not known how these proteins are secreted or how they become attached to the cell surface. A secretion system in which a large portion of the pool of each protein remains inside the cell while some of the pool of the protein is partitioned to the cell surface has not been identified. This may involve a novel version of a known secretion system or it may involve a novel secretion system. Understanding the processes by which intracellular/cell surface moonlighting proteins are targeted to the cell surface could provide novel protein targets for the development of small molecules that block secretion and/or association with the cell surface and could serve as lead compounds for the development of novel antibacterial therapeutics.

Recombinant Enolase of Trypanosoma cruzi as a Novel Vaccine Candidate against Chagas Disease in a Mouse Model of Acute Infection

Trypanosoma cruzi is the protozoan parasite that causes Chagas disease, which is considered by the World Health Organization to be a neglected tropical disease. Two drugs exist for the treatment of Chagas disease, nifurtimox and benznidazole; they are only effective in the acute phase, and a vaccine is currently not available. In this study, we used the recombinant enolase from T. cruzi H8 strain (MHOM/MX/1992/H8 Yucatán) (rTcENO) and its encoding DNA (pBKTcENO) to immunize mice and evaluate their protective effects in an experimental murine model of acute phase infection. Our results showed that mice vaccinated with rTcENO or its encoding DNA were able to generate typical specific antibodies (IgG1, IgG2a, and IgG2b), suggesting that a mixed Th1/Th2 immune response was induced. The parasite burden in the blood was reduced to 69.8% and 71% in mice vaccinated with rTcENO and pBKTcENO, respectively. The group vaccinated with rTcENO achieved 75% survival, in contrast to the group vaccinated with pBKTcENO that showed no survival in comparison to the control groups. Moreover, rTcENO immunization elevated the production of IFN-γ and IL-2 after the parasite challenge, suggesting that the Th1-type immune response was polarized. These results indicated that rTcENO could be used as a vaccine against Chagas disease.

Exploring the interaction between Mycobacterium tuberculosis enolase and human plasminogen using computational methods and experimental techniques

Surface localized microbial enolases' binding with human plasminogen has been increasingly proven to have an important role in initial infection cycle of several human pathogens. Likewise, surface localized Mycobacterium tuberculosis (Mtb) enolase also binds to human plasminogen, and this interaction may entail crucial consequences for granuloma stability. The current study is the first attempt to explore the plasminogen interacting residues of enolase from Mtb. Beginning with the structural modeling of Mtb enolase, the binding pose of Mtb enolase and human plasminogen was predicted using protein-protein docking simulations. The binding pose revealed the interface region with interacting residues and molecular interactions. Next, the interacting residues were refined and ranked by using various criteria. Finally, the selected interacting residues were tested experimentally for their involvement in plasminogen binding. The two consecutive lysine residues, Lys-193 and Lys-194, turned out to be active residues for plasminogen binding. These residues when substituted for alanine along with the most active residue Lys-429, that is, the triple mutant (K193A + K194A + K429A) Mtb enolase, exhibited 40% reduction in plasminogen binding. It is worth noting that Mtb enolase lost nearly half of the plasminogen binding activity with only three simultaneous substitutions, without any significant secondary structure perturbation. Further, the sequence comparison between Mtb and human enolase isoforms suggests the possibility of selective targeting of Mtb enolase to obstruct binding of human plasminogen.

Prevalence, virulence and antimicrobial resistance patterns of Aeromonas spp. isolated from children with diarrhea

BACKGROUND

Aeromonas spp. cause various intestinal and extraintestinal diseases. These bacteria are usually isolated from fecal samples, especially in children under five years old. The aim of this study was to assess the prevalence of Aeromonas spp. and their antimicrobial resistance profile in children with diarrhea referred to the Children Medical Center in Tehran, between 2013 and 2014.

METHODS

A total number of 391 stool samples were collected from children with ages between 1 day and 14 years old, with diarrhea (acute or chronic), referred to the Children Hospital, Tehran, Iran, between 2013 and 2014. Samples were enriched in alkaline peptone water broth for 24 hours at 37 °C and then cultured. Suspicious colonies were analyzed through biochemical tests. Furthermore, antimicrobial susceptibility tests were carried out for the isolates. Isolates were further studied for act, ast, alt, aerA and hlyA virulence genes using polymerase chain reaction.

RESULTS

In total, 12 isolates (3.1%) were identified as Aeromonas spp.; all were confirmed using the API-20E test. Of these isolates, five A. caviae (42%), four A. veronii (33%) and three A. hydrophila (25%) were identified in cases with gastroenteritis. Second to ampicillin (which was included in the growth medium used), the highest rate of antimicrobial resistance was seen against nalidixic acid and trimethoprim-sulfamethoxazole (5 isolates each, 41.6%) and the lowest rate of antimicrobial resistance was seen against gentamicin, amikacin and cefepime (none of the isolates). Results included 76.4% act, 64.7% ast, 71.5% alt, 83.3% aerA and 11.7% hlyA genes.

CONCLUSION

Aeromonas spp. are important due to their role in diarrhea in children; therefore, isolation and identification of these fecal pathogens should seriously be considered in medical laboratories. Since virulence genes play a significant role in gastroenteritis symptoms caused by these bacteria, Aeromonas species that include virulence genes are potentially suspected to cause severe infections. Moreover, bacterial antimicrobial resistance is increasing, especially against trimethoprim-sulfamethoxazole and nalidixic acid.

Enolase of Mycobacterium tuberculosis is a surface exposed plasminogen binding protein

BACKGROUND

Enolase, a glycolytic enzyme, has long been studied as an anchorless protein present on the surface of many pathogenic bacteria that aids in tissue remodeling and invasion by binding to host plasminogen.

METHODS

Anti-Mtb enolase antibodies in human sera were detected using ELISA. Immunoelectron microscopy, immunofluorescence microscopy and flow cytometry were used to show surface localization of Mtb enolase. SPR was used to determine the affinity of enolase-plasminogen interaction. Plasmin formation upon plasminogen binding to enolase and Mtb surface was measured by ELISA. Mice challenge and histopathological studies were undertaken to determine the protective efficacy of enolase immunization.

RESULTS

Enolase of Mtb is present on its surface and binds human plasminogen with high affinity. There was an average of 2-fold increase in antibody mediated recognition of Mtb enolase in human sera from TB patients with an active disease over control individuals. Substitution of C-terminal lysine to alanine in rEno decreased its binding affinity with human plasminogen by >2-folds. Enolase bound plasminogen showed urokinase mediated conversion into plasmin. Binding of plasminogen to the surface of Mtb and its conversion into fibrinolytic plasmin was significantly reduced in the presence of anti-rEno antibodies. Immunization with rEno also led to a significant decrease in lung CFU counts of mice upon infection with Mtb H37Rv.

CONCLUSIONS

Mtb enolase is a surface exposed plasminogen binding protein which upon immunization confers significant protection against Mtb challenge.

GENERAL SIGNIFICANCE

Plasminogen binding has been recognized for Mtb, however, proteins involved have not been characterized. We show here that Mtb enolase is a moonlighting plasminogen binding protein.

Virulence Factors of Aeromonas hydrophila: In the Wake of Reclassification

The ubiquitous "jack-of-all-trades," Aeromonas hydrophila, is a freshwater, Gram-negative bacterial pathogen under revision in regard to its phylogenetic and functional affiliation with other aeromonads. While virulence factors are expectedly diverse across A. hydrophila strains and closely related species, our mechanistic knowledge of the vast majority of these factors is based on the molecular characterization of the strains A. hydrophila AH-3 and SSU, which were reclassified as A. piscicola AH-3 in 2009 and A. dhakensis SSU in 2013. Individually, these reclassifications raise important questions involving the applicability of previous research on A. hydrophila virulence mechanisms; however, this issue is exacerbated by a lack of genomic data on other research strains. Collectively, these changes represent a fundamental gap in the literature on A. hydrophila and confirm the necessity of biochemical, molecular, and morphological techniques in the classification of research strains that are used as a foundation for future research. This review revisits what is known about virulence in A. hydrophila and the feasibility of using comparative genomics in light of this phylogenetic revision. Conflicting data between virulence factors, secretion systems, quorum sensing, and their effect on A. hydrophila pathogenicity appears to be an artifact of inappropriate taxonomic comparisons and/or be due to the fact that these properties are strain-specific. This review audits emerging data on dominant virulence factors that are present in both A. dhakensis and A. hydrophila in order to synthesize existing data with the aim of locating where future research is needed.

A Moonlighting Enolase from Lactobacillus gasseri does not Require Enzymatic Activity to Inhibit Neisseria gonorrhoeae Adherence to Epithelial Cells

Enolases are generally thought of as cytoplasmic enzymes involved in glycolysis and gluconeogenesis. However, several bacteria have active forms of enolase associated with the cell surface and these proteins are utilized for functions other than central metabolism. Recently, a surface-associated protein produced by Lactobacillus gasseri ATCC 33323 with homology to enolase was found to inhibit the adherence of the sexually transmitted pathogen, Neisseria gonorrhoeae, to epithelial cells in culture. Here, we show that the protein is an active enolase in vitro. A recombinantly expressed, C-terminal His-tagged version of the protein, His6-Eno3, inhibited gonococcal adherence. Assays utilizing inhibitors of enolase enzymatic activity showed that this inhibitory activity required the substrate-binding site to be in an open conformation; however, the enolase enzymatic activity of the protein was not necessary for inhibition of gonococcal adherence. An L. gasseri strain carrying an insertional mutation in eno3 was viable, indicating that eno3 is not an essential gene in L. gasseri 33323. This observation, along with the results of the enzyme assays, is consistent with reports that this strain encodes more than one enolase. Here we show that the three L. gasseri genes annotated as encoding an enolase are expressed. The L. gasseri eno3 mutant exhibited reduced, but not abolished, inhibition of gonococcal adherence, which supports the hypothesis that L. gasseri inhibition of gonococcal adherence is a multifactorial process.

Identification and characterization of an immunogenic antigen, enolase 2, among excretory/secretory antigens (ESA) of Toxoplasma gondii

An immunogenic protein, enolase 2, was identified among the secreted excretory/secretory antigens (ESAs) from Toxoplasma gondii strain RH using immunoproteomics based on matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. Enolase 2 was cloned, sequenced, and heterologously expressed. BLAST analysis revealed 75-96% similarity with enolases from other parasites. Immunoblotting demonstrated good immunoreactivity of recombinant T. gondii enolase (Tg-enolase 2) to T. gondii-infected animal serum. Purified Tg-enolase 2 was found to catalyze dehydration of 2-phospho-d-glycerate to phosphoenolpyruvate. In vitro studies revealed maximal activity at pH 7.5 and 37 °C, and activity was inhibited by K(+), Ni(2+), Al(3+), Na(+), Cu(2+) and Cr(3+). A monoclonal antibody against Tg-enolase 2 was prepared, 1D6, with the isotype IgG2a/κ. Western blotting revealed that 1D6 reacts with Tg-enolase 2 and native enolase 2, present among T. gondii ESAs. The indirect immunofluorescence assays showed that enolase 2 could be specifically detected on the growing T. gondii tachyzoites. Immunoelectron microscopy revealed the surface and intracellular locations of enolase 2 on T. gondii cells. In conclusion, our results clearly show that the enzymatic activity of T. gondii enolase 2 is ion dependent and that it could be influenced by environmental factors. We also provide evidence that enolase 2 is an important immunogenic protein of ESAs from T. gondii and that it is a surface-exposed protein with strong antigenicity and immunogenicity. Our findings indicate that enolase 2 could play important roles in metabolism, immunogenicity and pathogenicity and that it may serve as a novel drug target and candidate vaccine against T. gondii infection.

Detection of putative virulence genes of Lactococcus garvieae

Lactococcus garvieae is the causative agent of lactococcosis and has been isolated from a wide variety of animals. In the present study, 34 strains of L. garvieae isolated from fish from different sources and locations were tested for the presence or absence of the following putative virulence genes: a capsule gene cluster (CGC), hemolysins 1, 2, and 3 (hly1, -2, -3), NADH oxidase, superoxide dismutase (sod), phosphoglucomutase (pgm), adhesin Pav (adhPav), adhesin PsaA (adhPsaA), enolase (eno), LPxTG-containing surface proteins 1, 2, 3, and 4 (LPxTG-1, LPxTG-2, LPxTG-3, LPxTG-4; where LPxTG means Leu-Pro-any-Thr-Gly), adhesin clusters 1 and 2 (adhCI, adhCII), and adhesin (adh). To determine the presence of the CGC, we developed a multiplex PCR. All strains of L. garvieae had the hly1, -2, -3, NADH oxidase, pgm, adhPav, LPxTG-2, LPxTG-3, sod, eno, adhPsaA, adhCII, and adhCII genes, while only the Lg2 strain contained the CGC. The virulent Lg2 strain contained all 17 virulent genes. All Turkish, Spanish, Italian, and French strains did not contain the CGC. The multiplex PCR assay was useful for the detection of the CGC genes. In conclusion, the CGC is not the only virulent factor in L. garvieae because strains that lack the CGC are virulent to rainbow trout. Single genes also might not be responsible for the virulence of L. garvieae.

Lysine acetylation of major Chlamydia trachomatis antigens

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Chlamydia trachomatis causes trachoma and sexually transmitted diseases.

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Molecular mechanisms of chlamydial pathogenesis and immunity remain unclear.

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Acetylation of lysine is a post-translational modification that occurs in prokaryotes.

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Lysine acetylation sites were discovered in major chlamydial antigens.

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60 kDa chaperonin, EF-G and PmpB showed the highest degree of acetylation.

Chlamydia trachomatis (Ct) is a human pathogen causing trachoma and infertility. We investigated acetylation at lysine residues of chlamydial antigenic proteins: major outer membrane protein (MOMP), 60 kDa chaperonin (chlamydial Hsp60), elongation factor G (EF-G), enolase and the polymorphic membrane proteins PmpB, PmpE and PmpF. 60 kDa chaperonin, EF-G and PmpB showed the highest degree of acetylation.

Our data show that important Ct antigens could be post-translationally modified by acetylation of lysine residues at multiple sites. Further studies are needed to investigate total acetylome of Ct and the impact PTMs might have on Ct biology and pathogenicity.

Bacterial pathogens activate plasminogen to breach tissue barriers and escape from innate immunity

Both coagulation and fibrinolysis are tightly connected with the innate immune system. Infection and inflammation cause profound alterations in the otherwise well-controlled balance between coagulation and fibrinolysis. Many pathogenic bacteria directly exploit the host's hemostatic system to increase their virulence. Here, we review the capacity of bacteria to activate plasminogen. The resulting proteolytic activity allows them to breach tissue barriers and evade innate immune defense, thus promoting bacterial spreading. Yersinia pestis, streptococci of group A, C and G and Staphylococcus aureus produce a specific bacterial plasminogen activator. Moreover, surface plasminogen receptors play an established role in pneumococcal, borrelial and group B streptococcal infections. This review summarizes the mechanisms of bacterial activation of host plasminogen and the role of the fibrinolytic system in infections caused by these pathogens.

Genome-Wide Analysis of Oceanimonas sp. GK1 Isolated from Gavkhouni Wetland (Iran) Demonstrates Presence of Genes for Virulence and Pathogenicity

OBJECTIVE

The bacterium Oceanimonas sp. (O. sp.) GK1 is a member of the Aeromonadaceae family and its genome represents several virulence genes involved in fish and human pathogenicity. In this original research study we aimed to identify and characterize the putative virulence factors and pathogenicity of this halotolerant marine bacterium using genome wide analysis.

MATERIALS AND METHODS

The genome data of O. sp. GK1 was obtained from NCBI. Comparative genomic study was done using MetaCyc database.

RESULTS

Whole genome data analysis of the O. sp. GK1 revealed that the bacterium possesses some important virulence genes (e.g. ZOT, RTX toxin, thermostable hemolysin, lateral flagella and type IV pili) which have been implicated in adhesion and biofilm formation and infection in some other pathogenic bacteria.

CONCLUSION

This is the first report of the putative pathogenicity of O. sp.GK1. The genome wide analysis of the bacterium demonstrates the presence of virulence genes causing infectious diseases in many warmand cold-blooded animals.

Physical Features of Intracellular Proteins that Moonlight on the Cell Surface

Moonlighting proteins comprise a subset of multifunctional proteins that perform two or more biochemical functions that are not due to gene fusions, multiple splice variants, proteolytic fragments, or promiscuous enzyme activities. The project described herein focuses on a sub-set of moonlighting proteins that have a canonical biochemical function inside the cell and perform a second biochemical function on the cell surface in at least one species. The goal of this project is to consider the biophysical features of these moonlighting proteins to determine whether they have shared characteristics or defining features that might suggest why these particular proteins were adopted for a second function on the cell surface, or if these proteins resemble typical intracellular proteins. The latter might suggest that many other normally intracellular proteins found on the cell surface might also be moonlighting in this fashion. We have identified 30 types of proteins that have different functions inside the cell and on the cell surface. Some of these proteins are found to moonlight on the surface of multiple species, sometimes with different extracellular functions in different species, so there are a total of 98 proteins in the study set. Although a variety of intracellular proteins (enzymes, chaperones, etc.) are observed to be re-used on the cell surface, for the most part, these proteins were found to have physical characteristics typical of intracellular proteins. Many other intracellular proteins have also been found on the surface of bacterial pathogens and other organisms in proteomics experiments. It is quite possible that many of those proteins also have a moonlighting function on the cell surface. The increasing number and variety of known moonlighting proteins suggest that there may be more moonlighting proteins than previously thought, and moonlighting might be a common feature of many more proteins.

Novel insights into the pathogenicity of epidemic Aeromonas hydrophila ST251 clones from comparative genomics

Outbreaks in fish of motile Aeromonad septicemia (MAS) caused by Aeromonas hydrophila have caused a great concern worldwide. Here, for the first time, we provide two complete genomes of epidemic A. hydrophila strains isolated in China. To gain an insight into the pathogenicity of epidemic A. hydrophila, we performed comparative genomic analyses of five epidemic strains belonging to sequence type (ST) 251, together with the environmental strain ATCC 7966^T. We found that the known virulence factors, including a type III secretion system, a type VI secretion system and lateral flagella, are not required for the high virulence of the ST251 clonal group. Additionally, our work identifies three utilization pathways for myo-inositol, sialic acid and L-fucose providing clues regarding the factors that underlie the epidemic and virulent nature of ST251 A. hydrophila. Based on the geographical distribution and biological resources of the ST251 clonal group, we conclude that ST251 is a high-risk clonal group of A. hydrophila which may be responsible for the MAS outbreaks in China and the southeastern United States.

Altered Proteome of Burkholderia pseudomallei Colony Variants Induced by Exposure to Human Lung Epithelial Cells

Burkholderia pseudomallei primary diagnostic cultures demonstrate colony morphology variation associated with expression of virulence and adaptation proteins. This study aims to examine the ability of B. pseudomallei colony variants (wild type [WT] and small colony variant [SCV]) to survive and replicate intracellularly in A549 cells and to identify the alterations in the protein expression of these variants, post-exposure to the A549 cells. Intracellular survival and cytotoxicity assays were performed followed by proteomics analysis using two-dimensional gel electrophoresis. B. pseudomallei SCV survive longer than the WT. During post-exposure, among 259 and 260 protein spots of SCV and WT, respectively, 19 were differentially expressed. Among SCV post-exposure up-regulated proteins, glyceraldehyde 3-phosphate dehydrogenase, fructose-bisphosphate aldolase (CbbA) and betaine aldehyde dehydrogenase were associated with adhesion and virulence. Among the down-regulated proteins, enolase (Eno) is implicated in adhesion and virulence. Additionally, post-exposure expression profiles of both variants were compared with pre-exposure. In WT pre- vs post-exposure, 36 proteins were differentially expressed. Of the up-regulated proteins, translocator protein, Eno, nucleoside diphosphate kinase (Ndk), ferritin Dps-family DNA binding protein and peptidyl-prolyl cis-trans isomerase B were implicated in invasion and virulence. In SCV pre- vs post-exposure, 27 proteins were differentially expressed. Among the up-regulated proteins, flagellin, Eno, CbbA, Ndk and phenylacetate-coenzyme A ligase have similarly been implicated in adhesion, invasion. Protein profiles differences post-exposure provide insights into association between morphotypic and phenotypic characteristics of colony variants, strengthening the role of B. pseudomallei morphotypes in pathogenesis of melioidosis.

Modulation of α-enolase post-translational modifications by dengue virus: increased secretion of the basic isoforms in infected hepatic cells

Hepatic cells are major sites of dengue virus (DENV) replication and liver injury constitutes a characteristic of severe forms of dengue. The role of hepatic cells in dengue pathogenesis is not well established, but since hepatocytes are the major source of plasma proteins, changes in protein secretion by these cells during infection might contribute to disease progression. Previously, we showed that DENV infection alters the secretion pattern of hepatic HepG2 cells, with α-enolase appearing as one of the major proteins secreted in higher levels by infected cells. ELISA analysis demonstrated that DENV infection modulates α-enolase secretion in HepG2 cells in a dose-dependent manner, but has no effect on its gene expression and on the intracellular content of the protein as assessed by PCR and western blot analyses, respectively. Two-dimensional western blots showed that both intracellular and secreted forms of α-enolase appear as five spots, revealing α-enolase isoforms with similar molecular weights but distinct isoeletric points. Remarkably, quantification of each spot content revealed that DENV infection shifts the isoform distribution pattern of secreted α-enolase towards the basic isoforms, whereas the intracellular protein remains unaltered, suggesting that post-translational modifications might be involved in α-enolase secretion by infected cells. These findings provide new insights into the mechanisms underlying α-enolase secretion by hepatic cells and its relationship with the role of liver in dengue pathogenesis. In addition, preliminary results obtained with plasma samples from DENV-infected patients suggest an association between plasma levels of α-enolase and disease severity. Since α-enolase binds plasminogen and modulates its activation, it is plausible to speculate the association of the increase in α-enolase secretion by infected hepatic cells with the haemostatic dysfunction observed in dengue patients including the promotion of fibrinolysis and vascular permeability alterations.

Interactive host cells related to Mycoplasma suis α-enolase by yeast two-hybrid analysis

Mycoplasma suis belongs to the haemotrophic mycoplasmas, which colonise the red blood cells of a wide range of vertebrates. Adhesion to red blood cells is the crucial step in the unique lifecycle of M. suis. In addition to MSG1 protein, α-enolase is the second adhesion protein of M. suis, and may be involved in the adhesion of M. suis to porcine red blood cells (RBC). To simulate the environment of the RBC, we established the cDNA library of swine peripheral blood mononuclear cells (PBMC). The yeast two-hybrid (Y2H) system was adopted to screen α-enolase interactive proteins in the PBMC line. Alignment with the NCBI database revealed four interactive proteins: beta-actin, 60S ribosomal protein L11, clusterin precursor and endonuclease/reverse transcriptase. However, the M. suis α-enolase interactive proteins in the PBMC cDNA library obtained in the current study provide valuable information about the host cell interactions of the M. suis α-enolase protein.

Protein expression and transcription profiles of three strains of Aeromonas salmonicida ssp. salmonicida under normal and iron-limited culture conditions

Background

Aeromonas salmonicida is an important fish pathogen that produces a wide and varied array of virulence factors. Here we used iron deprivation by addition of the chelator 2’2-dipyridyl to induce the expression of several such virulence factors in three isolates of Aeromonas salmonicida (one avirulent and two virulent). By using SDS-PAGE followed by mass spectrometry, we identified proteins that appeared differentially expressed under these conditions. The differential transcription of the identified gene products were subsequently measured by reverse transcription quantitative real-time PCR (RT-qPCR).

Results

Our initial screening using SDS-PAGE identified five proteins that appeared differentially expressed in virulent and avirulent isolates or, within the same isolates, between bacteria cultivated under iron-rich or iron-deprived conditions. The transcription of the genes coding for these proteins were subsequently quantified by RT-qPCR. Results of this analysis demonstrated that the gene coding for alkyl hydroperoxide reductase (AhpC), a protein involved in oxidative stress response, was transcribed at a higher rate in the virulent strain as compared to the avirulent strain. Additionally, it was observed that addition of an iron chelator to the culture medium lead to a reduction of the transcription levels of the regulatory histone-like nucleoid structuring protein (H-NS). This was consistent in all three isolates. On the other hand, the transcription levels of the virulence array protein (VapA) and the protein ATP-synthetase F (ATPF) displayed only limited changes, despite being the dominant component of a protein fraction that displayed changes during the preliminary SDS-PAGE screening. This was true regardless of the culture conditions and of the isolates considered. Finally, transcription of the enzyme enolase was upregulated in the iron-deprived broths in all isolates.

Conclusions

We identified several genes differentially expressed under culture conditions known to lead to the overexpression of virulence factors. In addition, we identified alkyl hydroperoxide as being overexpressed in the virulent isolates compared to the avirulent isolates. The results from this study will contribute to enhance our understanding of the virulence of A. salmonicida and may suggest new directions for further research.

Parasitism in optima forma: exploiting the host fibrinolytic system for invasion

The interaction of pathogenic bacteria with the host fibrinolytic system through the plasminogen molecule has been well documented. It has been shown, using animal models, to be important in invasion into the host and establishment of the infection. From a number of recent observations with parasitic protists and helminths, emerges evidence that also in these organisms the interaction with plasminogen may be important for infection and virulence. A group of molecules that act as plasminogen receptors have been identified in parasites. This group comprises the glycolytic enzymes enolase, glyceraldehyde-3-phosphate dehydrogenase and fructose-1,6-biphosphate aldolase, in common with the plasminogen receptors known in prokaryotic pathogens. The interaction with the fibrinolytic system may arm the parasites with the host protease plasmin, thus helping them to migrate and cross barriers, infect cells and avoid clot formation. In this context, plasminogen receptors on the parasite surface or as secreted molecules, may be considered virulence factors. A possible evolutionary scenario for the recruitment of glycolytic enzymes as plasminogen receptors by widely different pathogens is discussed.

Genomic study of polyhydroxyalkanoates producing Aeromonas hydrophila 4AK4

The complete genome of Gram-negative Aeromonas hydrophila 4AK4 that has been used for industrial production of poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) was sequenced and annotated. Its chromosome is 4,527,993 bp in size encoding 4,272 genes, including 28 rRNA genes and 104 tRNA genes. Comparative analysis indicated that genome of A. hydrophila 4AK4 was similar to that of the A. hydrophila ATCC 7966(T), an intensively studied aeromonad for its pathogenicity related to its genomic information. Genes possibly coming from other species or even other genus were identified in A. hydrophila 4AK4. A large number of putative virulent genes were predicted. However, a cytotonic enterotoxin (Ast) is absent in A. hydrophila 4AK4, allowing the industrial strain to be different from other A. hydrophila strains, indicating possible reduced virulence of strain 4AK4, which is very important for industrial fermentation. Genes involved in polyhydroxyalkanoate (PHA) metabolism were predicted and analyzed. The resulting genomic information is useful for improved production of PHA via metabolic engineering of A. hydrophila 4AK4.

Food vacuole associated enolase in plasmodium undergoes multiple post-translational modifications: evidence for atypical ubiquitination

Plasmodium enolase localizes to several sub-cellular compartments viz. cytosol, nucleus, cell membrane, food vacuole (FV) and cytoskeleton, without having any organelle targeting signal sequences. This enzyme has been shown to undergo multiple post-translational modifications (PTMs) giving rise to several variants that show organelle specific localization. It is likely that these PTMs may be responsible for its diverse distribution and moonlighting functions. While most variants have a MW of ~50 kDa and are likely to arise due to changes in pI, food vacuole (FV) associated enolase showed three forms with MW~50, 65 and 75 kDa. Evidence from immuno-precipitation and western analysis indicates that the 65 and 75 kDa forms of FV associated enolase are ubiquitinated. Using mass spectrometry (MS), definitive evidence is obtained for the nature of PTMs in FV associated variants of enolase. Results showed several modifications, viz. ubiquitination at K147, phosphorylation at Y148 and acetylation at K142 and K384. MS data also revealed the conjugation of three ubiquitin (Ub) molecules to enolase through K147. Trimeric ubiquitin has a linear peptide linkage between the NH₂-terminal methionine of the first ubiquitin (Ub1) and the C-terminal G76 of the second (Ub2). Ub2 and third ubiquitin (Ub3) were linked through an atypical isopeptide linkage between K6 of Ub2 and G76 of Ub3, respectively. Further, the tri-ubiquitinated form was found to be largely associated with hemozoin while the 50 and 65 kDa forms were present in the NP-40 soluble fraction of FV. Mass spectrometry results also showed phosphorylation of S42 in the cytosolic enolase from P. falciparum and T337 in the cytoskeleton associated enolase from P. yoelii. The composition of food vacuolar proteome and likely interactors of enolase are also being reported.