Expression of glyceraldehyde-3-phosphate dehydrogenase on the surface of Clostridium perfringens cells

Autolysin as a fibronectin receptor on the cell surface of Clostridium perfringens

OBJECTIVE

Clostridium perfringens causes food poisoning and gas gangrene, a serious wound-associated infection. C. perfringens cells adhere to collagen via fibronectin (Fn). We investigated whether the peptidoglycan hydrolase of C. perfringens, i.e., autolysin (Acp), is implicated in Fn binding to C. perfringens cells.

METHODS

This study used recombinant Acp fragments, human Fn and knockout mutants (C. perfringens 13 acp::erm and HN13 ΔfbpC ΔfbpD). Ligand blotting, Western blotting analysis, and complementation tests were performed. The Fn-binding activity of each mutant was evaluated by ELISA.

RESULTS

From an Fn-binding assay using recombinant Acp fragments, Fn was found to bind to the catalytic domain of Acp. In mutant cells lacking Acp, Fn binding was significantly decreased, but was restored by the complementation of the acp gene. There are three known kinds of Fn-binding proteins in C. perfringens: FbpC, FbpD, and glyceraldehyde-3-phosphate dehydrogenase. We found no difference in Fn-binding activity between the mutant cells lacking both FbpC and FbpD (SAK3 cells) and the wild-type cells, indicating that these Fn-binding proteins are not involved in Fn binding to C. perfringens cells.

CONCLUSIONS

We found that the Acp is an Fn-binding protein that acts as an Fn receptor on the surface of C. perfringens cells.

Hijacking of Host Plasminogen by Mesomycoplasma (Mycoplasma) hyopneumoniae via GAPDH: an Important Virulence Mechanism To Promote Adhesion and Extracellular Matrix Degradation

Mesomycoplasma hyopneumoniae is the etiological agent of mycoplasmal pneumonia of swine (MPS), which causes substantial economic losses to the world's swine industry. Moonlighting proteins are increasingly being shown to play a role in the pathogenic process of M. hyopneumoniae. Glyceraldehyde-3-phosphate dehydrogenase (GAPDH), a key enzyme in glycolysis, displayed a higher abundance in a highly virulent strain of M. hyopneumoniae than in an attenuated strain, suggesting that it may have a role in virulence. The mechanism by which GAPDH exerts its function was explored. Flow cytometry and colony blot analysis showed that GAPDH was partly displayed on the surface of M. hyopneumoniae. Recombinant GAPDH (rGAPDH) was able to bind PK15 cells, while the adherence of a mycoplasma strain to PK15 was significantly blocked by anti-rGAPDH antibody pretreatment. In addition, rGAPDH could interact with plasminogen. The rGAPDH-bound plasminogen was demonstrated to be activated to plasmin, as proven by using a chromogenic substrate, and to further degrade the extracellular matrix (ECM). The critical site for GAPDH binding to plasminogen was K336, as demonstrated by amino acid mutation. The affinity of plasminogen for the rGAPDH C-terminal mutant (K336A) was significantly decreased according to surface plasmon resonance analysis. Collectively, our data suggested that GAPDH might be an important virulence factor that facilitates the dissemination of M. hyopneumoniae by hijacking host plasminogen to degrade the tissue ECM barrier. IMPORTANCE Mesomycoplasma hyopneumoniae is a specific pathogen of pigs that is the etiological agent of mycoplasmal pneumonia of swine (MPS), which is responsible for substantial economic losses to the swine industry worldwide. The pathogenicity mechanism and possible particular virulence determinants of M. hyopneumoniae are not yet completely elucidated. Our data suggest that GAPDH might be an important virulence factor in M. hyopneumoniae that facilitates the dissemination of M. hyopneumoniae by hijacking host plasminogen to degrade the extracellular matrix (ECM) barrier. These findings will provide theoretical support and new ideas for the research and development of live-attenuated or subunit vaccines against M. hyopneumoniae.

Development of an in vitro Model of Human Gut Microbiota for Screening the Reciprocal Interactions With Antibiotics, Drugs, and Xenobiotics

Altering the gut microbiota can negatively affect human health. Efforts may be sustained to predict the intended or unintended effects of molecules not naturally produced or expected to be present within the organism on the gut microbiota. Here, culture-dependent and DNA-based approaches were combined to UHPLC-MS/MS analyses in order to investigate the reciprocal interactions between a constructed Human Gut Microbiota Model (HGMM) and molecules including antibiotics, drugs, and xenobiotics. Our HGMM was composed of strains from the five phyla commonly described in human gut microbiota and belonging to Firmicutes, Bacteroidetes, Proteobacteria, Fusobacteria, and Actinobacteria. Relevantly, the bacterial diversity was conserved in our constructed human gut model through subcultures. Uneven richness distribution was revealed and the sensitivity of the HGMM was mainly affected by antibiotic exposure rather than by drugs or xenobiotics. Interestingly, the constructed model and the individual cultured strains respond with the same sensitivity to the different molecules. UHPLC-MS/MS analyses revealed the disappearance of some native molecules in the supernatants of the HGMM as well as in those of the individual strains. These results suggest that biotransformation of molecules occurred in the presence of our gut microbiota model and the coupled approaches performed on the individual cultures may emphasize new bacterial strains active in these metabolic processes. From this study, the new HGMM appears as a simple, fast, stable, and inexpensive model for screening the reciprocal interactions between the intestinal microbiota and molecules of interest.

Putative antigenic proteins identified by comparative and subtractive reverse vaccinology in necrotic enteritis-causing Clostridium perfringens isolated from broiler chickens

BACKGROUND

Avian necrotic enteritis (NE) caused by Clostridium perfringens is a disease with a major economic impact, generating losses estimated to 6 billion of dollars annually for the poultry industry worldwide. The incidence of the disease is particularly on the rise in broiler chicken flocks eliminating the preventive use of antibiotics. To date, no alternative allows for the efficient prevention of NE and a control of the disease using a vaccinal strategy would be mostly prized. For this purpose, comparative and subtractive reverse vaccinology identifying putative immunogenic bacterial surface proteins is one of the most promising approaches.

RESULTS

A comparative genomic study was performed on 16 C. perfringens strains isolated from healthy broiler chickens and from broilers affected with necrotic enteritis. Results showed that the analyzed genomes were composed of 155,700 distinct proteins from which 13% were identified as extracellular, 65% as cytoplasmic and 22% as part of the bacterial membrane. The evaluation of the immunogenicity of these proteins was determined using the prediction software VaxiJen®.

CONCLUSIONS

For the most part, proteins with the highest scores were associated with an extracellular localisation. For all the proteins analyzed, the combination of both the immunogenicity score and the localisation prediction led to the selection of 12 candidate proteins that were mostly annotated as hypothetical proteins. We describe 6 potential candidates of higher interest due to their antigenic potential, their extracellular localisation, and their possible role in virulence of C. perfringens.

Abiotrophia defectiva DnaK Promotes Fibronectin-Mediated Adherence to HUVECs and Induces a Proinflammatory Response

Abiotrophia defectiva is a nutritionally variant streptococci that is found in the oral cavity, and it is an etiologic agent of infective endocarditis. We have previously reported the binding activity of A. defectiva to fibronectin and to human umbilical vein endothelial cells (HUVECs). However, the contribution of some adhesion factors on the binding properties has not been well delineated. In this study, we identified DnaK, a chaperon protein, as being one of the binding molecules of A. defectiva to fibronectin. Recombinant DnaK (rDnaK) bound immobilized fibronectin in a concentration-dependent manner, and anti-DnaK antiserum reduced the binding activity of A. defectiva with both fibronectin and HUVECs. Furthermore, DnaK were observed on the cell surfaces via immune-electroscopic analysis with anti-DnaK antiserum. Expression of IL-8, CCL2, ICAM-1, and VCAM-1 was upregulated with the A. defectiva rDnaK treatment in HUVECs. Furthermore, TNF-α secretion of THP-1 macrophages was also upregulated with the rDnaK. We observed these upregulations in rDnaK treated with polymyxin B, but not in the heat-treated rDnaK. The findings show that A. defectiva DnaK functions not only as an adhesin to HUVECs via the binding to fibronectin but also as a proinflammatory agent in the pathogenicity to cause infective endocarditis.

Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) moonlights as an adhesin in Mycoplasma hyorhinis adhesion to epithelial cells as well as a plasminogen receptor mediating extracellular matrix degradation

Mycoplasma hyorhinis infects pigs causing polyserositis and polyarthritis, and has also been reported in a variety of human tumor tissues. The occurrence of disease is often linked with the systemic invasion of the pathogen. Glyceraldehyde-3-Phosphate Dehydrogenase (GAPDH), one of the key enzymes of glycolysis, was reported as a surface multifunctional molecule in several bacteria. Here, we investigated whether GAPDH could manifest binary functions; as an adhesin to promote colonization as well as a plasminogen receptor functioning in extracellular matrix (ECM) degradation to promote systemic invasion. The surface localization of GAPDH was observed in M. hyorhinis with flow cytometry and colony blot analysis. Recombinant GAPDH (rGAPDH) was found to be able to bind porcine-derived PK-15 and human-derived NCI-H292 cells. The incubation with anti-GAPDH antibody significantly decreased the adherence of M. hyorhinis to both cell lines. To investigate its function in recruiting plasminogen, firstly, the interaction between rGAPDH and plasminogen was demonstrated by ELISA and Far-Western blot assay. The activation of the rGAPDH-bound plasminogen into plasmin was proved by using a chromogenic substrate, and furtherly confirmed to degrade extracellular matrix by using a reconstituted ECM. Finally, the ability of rGAPDH to bind different ECM components was demonstrated, including fibronectin, laminin, collagen type IV and vitronectin. Collectively, our data imply GAPDH as an important adhesion factor of M. hyrohinis and a receptor for hijacking host plasminogen to degrade ECM. The multifunction of GAPDH to bind both plasminogen and ECM components is believed to increase the targeting of proteolysis and facilitate the dissemination of M. hyorhinis.

Evaluation of different antigenic preparations against necrotic enteritis in broiler birds using a novel Clostridium perfringens type G strain

OBJECTIVE

Keeping in view, the constraints faced by the Indian broiler industry with lack of a suitable vaccine against Necrotic Enteritis (NE), a study has been proposed to explore the prevalence and detail characterization of C. perfringens type G in NE suspected broiler chicken in the process of suitable vaccine development.

METHODS

Intestinal scrapings/faecal contents of NE suspected broiler chickens were screened to establish the prevalence of C.perfringens type G in broiler birds. A most pathogenic, highly resistant type G isolate of C. perfringens, bearing both tpeL and gapC gene was selected for preparation of three different vaccine formulations, and to evaluate their immunogenic potential in broiler birds.

RESULTS

Screening of clinical samples of NE suspected broiler birds revealed C. perfringens type G, bearing gapC gene in 51.22% samples, of which 47.62% revealed tpeL gene. Seven of the tpeL^pos type G isolates were comparatively more pathogenic for mice, of which, one exhibited multidrug resistance towards ciprofloxacin, norfloxacin, tetracycline and levofloxacin. The sonicated supernatant (SS) prepared from the selected tpeL and gapC positive isolate could maintain a significantly higher protective IgG response than toxoid and bacterin preparation from the 21st to 28^thday of age in immunized birds.

CONCLUSION

The additional TpeL toxin in C. perfringens type G has been proved to be an additional key biological factor in the pathogenesis of NE in broiler chickens. Considering the release of more immunogenic proteins, the SS proved to be a better immunogenic preparation against NE with a multiple immunization dose.

Effects from diet-induced gut microbiota dysbiosis and obesity can be ameliorated by fecal microbiota transplantation: A multiomics approach

Obesity and its comorbidities are currently considered an epidemic, and the involved pathophysiology is well studied. Hypercaloric diets are tightly related to the obesity etiology and also cause alterations in gut microbiota functionality. Diet and antibiotics are known to play crucial roles in changes in the microbiota ecosystem and the disruption of its balance; therefore, the manipulation of gut microbiota may represent an accurate strategy to understand its relationship with obesity caused by diet. Fecal microbiota transplantation, during which fecal microbiota from a healthy donor is transplanted to an obese subject, has aroused interest as an effective approach for the treatment of obesity. To determine its success, a multiomics approach was used that combined metagenomics and metaproteomics to study microbiota composition and function. To do this, a study was performed in rats that evaluated the effect of a hypercaloric diet on the gut microbiota, and this was combined with antibiotic treatment to deplete the microbiota before fecal microbiota transplantation to verify its effects on gut microbiota-host homeostasis. Our results showed that a high-fat diet induces changes in microbiota biodiversity and alters its function in the host. Moreover, we found that antibiotics depleted the microbiota enough to reduce its bacterial content. Finally, we assessed the use of fecal microbiota transplantation as a complementary obesity therapy, and we found that it reversed the effects of antibiotics and reestablished the microbiota balance, which restored normal functioning and alleviated microbiota disruption. This new approach could be implemented to support the dietary and healthy habits recommended as a first option to maintain the homeostasis of the microbiota.

Plasminogen-binding proteins as an evasion mechanism of the host's innate immunity in infectious diseases

Pathogens have developed particular strategies to infect and invade their hosts. Amongst these strategies’ figures the modulation of several components of the innate immune system participating in early host defenses, such as the coagulation and complement cascades, as well as the fibrinolytic system. The components of the coagulation cascade and the fibrinolytic system have been proposed to be interfered during host invasion and tissue migration of bacteria, fungi, protozoa, and more recently, helminths. One of the components that has been proposed to facilitate pathogen migration is plasminogen (Plg), a protein found in the host’s plasma, which is activated into plasmin (Plm), a serine protease that degrades fibrin networks and promotes degradation of extracellular matrix (ECM), aiding maintenance of homeostasis. However, pathogens possess Plg-binding proteins that can activate it, therefore taking advantage of the fibrin degradation to facilitate establishment in their hosts. Emergence of Plg-binding proteins appears to have occurred in diverse infectious agents along evolutionary history of host–pathogen relationships. The goal of the present review is to list, summarize, and analyze different examples of Plg-binding proteins used by infectious agents to invade and establish in their hosts. Emphasis was placed on mechanisms used by helminth parasites, particularly taeniid cestodes, where enolase has been identified as a major Plg-binding and activating protein. A new picture is starting to arise about how this glycolytic enzyme could acquire an entirely new role as modulator of the innate immune system in the context of the host–parasite relationship.