Mycoplasma hyopneumoniae evades complement activation by binding to factor H via elongation factor thermo unstable (EF-Tu)

HylS', a fragment of truncated hyaluronidase of Streptococcus suis, contributes to immune evasion by interaction with host complement factor C3b

Pathogenic bacteria have evolved many strategies to evade surveillance and attack by complements. Streptococcus suis is an important zoonotic pathogen that infects humans and pigs. Hyaluronidase (HylA) has been reported to be a potential virulence factor of S. suis. However, in this study, it was discovered that the genomic region encoding HylA of the virulent S. suis strain SC19 and other ST1 strains was truncated into four fragments when aligned with a strain containing intact HylA and possessing hyaluronidase activity. As a result, SC19 had no hyaluronidase activity, but one truncated HylA fragment, designated as HylS,' directly interacted with complement C3b, as confirmed by western ligand blotting, pull-down, and ELISA assays. The deposition of C3b and membrane attack complex (MAC) formation on the surface of a HylS'-deleted mutant (ΔhylS') was significantly increased compared to wild-type SC19. In human sera and whole blood, ΔhylS' survival was significantly reduced compared to that in SC19. The resistance of ΔhylS' to macrophages and human polymorphonuclear neutrophil PMNs also decreased. In a mouse infection model, ΔhylS' showed reduced lethality and lower bacterial load in the organs compared to that of SC19. We conclude that the truncated hyaluronidase HylS' fragment contributes to complement evasion and the pathogenesis of S. suis.

Comparative genomic analysis of Brazilian Mesomycoplasma ovipneumoniae strains revealed genomic differences associated with the geographic origin and health status and mutations in the gyrA

Sheep respiratory disease (SRD) is a multifactorial illness commonly affecting sheep. Mesomycoplasma (Mycoplasma) ovipneumoniae is one of the most important etiological agents of SRD and should be better understood, especially in countries where it was recently detected, such as Brazil. Also, the intensive use of quinolones in mycoplasmal infections increases the selective pressure for resistance to this drug class, and no data about antimicrobial resistance in Brazil is available. Therefore, this study aimed to perform a comparative genomic analysis of newly isolated Brazilian M. ovipneumoniae strains, identify point mutations in target genes that may be associated with antibiotic resistance, and perform a phylogenomic analysis of these strains with available genome representatives of M. ovipneumoniae. Glucose-fermenting fried egg-like colonies identified as M. ovipneumoniae were obtained after a culture of tracheobronchial lavage from infected sheep. The genomes were sequenced, de novo assembled and comparatively evaluated. Important putative virulence factors were detected in all isolates: the analysis of the average nucleotide homology of all these genes with the M. ovipneumoniae ATCC 29419 revealed associations between clpB, lgt, tuf, and dnaJ genes and geographic location. In addition, nucleotide substitutions in a few positions of the Quinolone-Resistant Determinant Region of the gyrA gene, including the Ser83Ala, were detected. The phylogenomic analysis showed that the Brazilian isolates belonged to two different clades corresponding to geographic location, and the isolates from São Paulo showed high similarity, which differs from isolates from Rio de Janeiro. This first genomic analysis of the Brazilian M. ovipneumoniae genomes demonstrates strain segregation according to location and health status, reinforcing the importance of continuous surveillance and diagnostics of this bacteria causing sheep respiratory disease in the Brazilian flocks.

Research Progress on Immune Evasion of Mycoplasma hyopneumoniae

As the main pathogen associated with enzootic pneumonia (EP), Mycoplasma hyopneumoniae (Mhp) is globally prevalent and inflicts huge financial losses on the worldwide swine industry each year. However, the pathogenicity of Mhp has not been fully explained to date. Mhp invasion usually leads to long-term chronic infection and persistent lung colonization, suggesting that Mhp has developed effective immune evasion strategies. In this review, we offer more detailed information than was previously available about its immune evasion mechanisms through a systematic summary of the extant findings. Genetic mutation and post-translational protein processing confer Mhp the ability to alter its surface antigens. With the help of adhesins, Mhp can achieve cell invasion. And Mhp can modulate the host immune system through the induction of inflammation, incomplete autophagy, apoptosis, and the suppression of immune cell or immune effector activity. Furthermore, we offer the latest views on how we may treat Mhp infections and develop novel vaccines.

Exploring the pathogenetic mechanisms of Mycoplasmapneumoniae (Review)

Mycoplasmas, the smallest self-replicating prokaryotes without a cell wall, are the most prevalent and extensively studied species in humans. They significantly contribute to chronic respiratory tract illnesses and pneumonia, with children and adolescents being particularly vulnerable. Mycoplasma pneumoniae (M. pneumoniae) infections typically tend to be self-limiting and mild but can progress to severe or even life-threatening conditions in certain individuals. Extrapulmonary effects often occur without pneumonia, and both intrapulmonary and extrapulmonary complications operate through separate pathological mechanisms. The indirect immune-mediated damage of the immune system, vascular blockages brought on by vasculitis or thrombosis and direct harm from invasion or locally induced inflammatory cytokines are potential causes of extrapulmonary manifestations due to M. pneumoniae. Proteins associated with adhesion serve as the primary factor crucial for the pathogenicity of M. pneumoniae, relying on a specialized polarized terminal attachment organelle. The type and density of these host receptors significantly impact the adhesion and movement of M. pneumoniae, subsequently influencing the pathogenic mechanism and infection outcomes. Adjacent proteins are crucial for the proper assembly of the attachment organelle, with variations in the genetic domains of P1, P40 and P90 surfaces contributing to the variability of clinical symptoms and offering new avenues for developing vaccines against M. pneumoniae infections. M. pneumoniae causes oxidative stress within respiratory tract epithelial cells by adhering to host cells and releasing hydrogen peroxide and superoxide radicals. This oxidative stress enhances the vulnerability of host cells to harm induced by oxygen molecules. The lack of superoxide dismutase and catalase of bacteria allows it to hinder the catalase activity of the host cell, leading to the reduced breakdown of peroxides. Lung macrophages play a significant role in managing M. pneumoniae infection, identifying it via Toll-like receptor 2 and initiating the myeloid differentiation primary response gene 88-nuclear factor κΒ signaling cascade. However, the precise mechanisms enabling M. pneumoniae to evade intracellular host defenses remain unknown, necessitating further exploration of the pathways involved in intracellular survival. The present comprehensive review delves into the pathogenesis of M. pneumoniae infection within the pulmonary system and into extrapulmonary areas, outlining its impact.

Screening inhibitors against the Ef-Tu of Fusobacterium nucleatum: a docking, ADMET and PBPK assessment study

The oral pathogen Fusobacterium nucleatum has recently been associated with an elevated risk of colorectal cancer (CRC), endometrial metastasis, chemoresistance, inflammation, metastasis, and DNA damage, along with several other diseases. This study aimed to explore the disruption of protein machinery of F. nucleatum via inhibition of elongation factor thermo unstable (Ef-Tu) protein, through natural products. No study on Ef-Tu inhibition by natural products or in Fusobacterium spp. exists till todate. Ef-Tu is an abundant specialized drug target in bacteria that varies from human Ef-Tu. Elfamycins target Ef-Tu and hence, Enacyloxin IIa was used to generate pharmacophore for virtual screening of three natural product libraries, Natural Product Activity and Species Source (NPASS) (n = 30000 molecules), Tibetan medicinal plant database (n = 54 molecules) and African medicinal plant database (n > 6000 molecules). Peptaibol Septocylindrin B (NPC141050), Hirtusneanoside, and ZINC95486259 were prioritized from these libraries as potential therapeutic candidates. ADMET profiling was done for safety assessment, physiological-based pharmacokinetic modeling in human and mouse for getting insight into drug interaction with body tissues and molecular dynamics was used to assess stability of the best hit NPC141050 (Septocylindrin B). Based on the promising results, we propose further in vitro, in vivo and pharmacokinetic testing on the lead Septocylindrin B, for possible translation into therapeutic interventions.

Mycoplasma synoviae lipid-associated membrane proteins identification and expression changes when exposed to chicken cells

Mycoplasma synoviae is a significant cause of respiratory disease and synovitis among chickens, and has an adverse economic impact on broiler breeding efforts. The present study was designed to develop a systematic understanding of the role that M. synoviae lipid-associated membrane proteins (LAMPs) may play in the virulence of this pathogen. Bioinformatics tools were used to identify 146 predicted membrane proteins and lipoproteins in the M. synoviae proteome. Then, Triton X-114 was used to extract LAMPs that were subsequently identified via LC-MS/MS. This approach enabled the detection of potential LAMPs, and the top 200 most abundant proteins detected using this strategy were subject to further analysis. M. synoviae cells (100 MOI) were exposed to chicken fibroblasts (DF-1) and macrophages (HD-11) in a 1:1 mixed culture. Analysis of LAMP transcripts identified 72 up-regulated LAMP genes which were analyzed in depth by bioinformatics. GO analysis revealed these genes to be enriched in the nucleotide binding, sulfur amino acid transmembrane transporter activity, tRNA binding, rRNA modification, and transition metal ion transport pathways. Moreover, KEGG enrichment analysis suggested that these genes were enriched in the biosynthesis of secondary metabolites, carbon metabolism, glycolysis/gluconeogenesis, and nitrogen metabolism pathways.

Mycoplasma pneumoniae: Among the smallest bacterial pathogens with great clinical significance in children

BACKGROUND

Mycoplasmas are the smallest prokaryotic microorganisms found in nature. Mycoplasma pneumoniae (M. pneumoniae) is the most commonly studied among human mycoplasmas.

OBJECTIVES

In this review, we briefly focus on the recent developments that have enhanced our understanding of M. pneumoniae, one of the smallest pathogenic bacteria of great clinical importance in children.

CONTENT

M. pneumoniae infections may involve either upper or lower respiratory tract or both of them. Extrapulmonary manifestations have been reported in almost every organ, including the skin and the hematologic, cardiovascular, musculoskeletal, and nervous system due to direct local effects, after dissemination of bacteria or indirect effects. The correct identification of M. pneumoniae infections is vital for prescription of the appropriate therapy.There are scarce specific findings of clinical laboratory results for the diagnosis of M. pneumoniae infection. Detection of M. pneumoniae infections can be achieved using culture, serology, or molecular-based methods. Culture is time-consuming, laborious, and expensive. The major types of serological tests for M. pneumoniae include the microtiter plate enzyme immunoassay (EIA), the membrane EIA, indirect immunofluorescence, and particle agglutination. Nucleic acid amplification tests (NAATs) include traditional PCR, nested PCR, real-time quantitative PCR, nucleic acid sequence-based amplification (NASBA), loop-mediated isothermal amplification (LAMP) technology, and RNA simultaneous amplification and testing (SAT). Macrolides have been the drug of choice for treating M. pneumoniae infection in past years. Clinically significant acquired macrolide-resistant M. pneumoniae (MRMP)has emerged worldwide which may be associated with more extrapulmonary complications, and severe clinical and radiological features. Since molecular-based assays can detect M. pnueumoniae in clinical specimens, there is a need for real point of care testing for fast detection of M. pneumoniae or its DNA and mutations in macrolide resistance gene. It is necessary to develop safe vaccines that provide protective immunity against M.pneumoniae infection.

Unveiling the stealthy tactics: mycoplasma's immune evasion strategies

Mycoplasmas, the smallest known self-replicating organisms, possess a simple structure, lack a cell wall, and have limited metabolic pathways. They are responsible for causing acute or chronic infections in humans and animals, with a significant number of species exhibiting pathogenicity. Although the innate and adaptive immune responses can effectively combat this pathogen, mycoplasmas are capable of persisting in the host, indicating that the immune system fails to eliminate them completely. Recent studies have shed light on the intricate and sophisticated defense mechanisms developed by mycoplasmas during their long-term co-evolution with the host. These evasion strategies encompass various tactics, including invasion, biofilm formation, and modulation of immune responses, such as inhibition of immune cell activity, suppression of immune cell function, and resistance against immune molecules. Additionally, antigen variation and molecular mimicry are also crucial immune evasion strategies. This review comprehensively summarizes the evasion mechanisms employed by mycoplasmas, providing valuable insights into the pathogenesis of mycoplasma infections.

Mannheimia haemolytica increases Mycoplasma bovis disease in a bovine experimental model of BRD

Amongst the bacterial pathogens associated with the bovine respiratory disease syndrome (BRD) in cattle are Mannheimia haemolytica and Mycoplasma bovis. The interaction between these two pathogens has not been investigated before; thus, there are gaps in the knowledge of why and how a previous infection with M. haemolytica allows the development of M. bovis-related lesions. We hypothesized that upon M. haemolytica infection, inflammatory products are produced in the lung and that these inflammatory products stimulate M. bovis to produce proteases and lipases that degrade lipids and proteins important for lung function. In this work, we identified several M. bovis proteases and lipases whose expression was modulated by M. haemolytica products in vitro. We performed co-infection animal challenges to develop a model to test vaccine protection. A prior exposure to BHV-1 followed by infection with M. bovis and M. haemolytica resulted in severe pathology and the BHV-1 infection was abandoned. When M. bovis and M. haemolytica were introduced into the lungs by bronchoscopy, we found that M. haemolytica resulted in worsening of the respiratory disease caused by M. bovis. We performed a proof-of-concept trial where animals were immunized with the M. bovis proteins identified in this study and challenged with both pathogens. Despite detecting significant humoral immune responses to the antigens, the experimental vaccine failed to protect against M. bovis disease.

Complement-mediated killing of Mycoplasma bovis does not play a role in the protection of animals against an experimental challenge

Despite numerous efforts, developing recombinant vaccines for the control of M. bovis infections has not been successful. Many factors are contributing to the lack of success including the identification of protective antigens, use of effective adjuvants, and relatively limited information on the quality of immune responses needed for protection. Experimental trials using vaccination with many M. bovis proteins resulted in significant humoral immune responses before and after the challenges, however these responses were not enough to confer protection. We explored the role of complement-fixing antibodies in the killing of M. bovis in-vitro and whether animals vaccinated with proteins that elicit antibodies capable of complement-fixing would be protected against an experimental challenge. We found that antibodies against some of these proteins fixed complement and killed M. bovis in-vitro. Vaccination and challenge experiments with proteins whose cognate antibodies either fixed complement or not resulted in lack of protection against a M. bovis experimental challenge suggesting that complement fixation does not play a role in protection.

Insight into the Pathogenic Mechanism of Mycoplasma pneumoniae

Mycoplasma pneumoniae, an obligate parasitic pathogen without cell wall, can cause severe upper and lower respiratory tract symptoms. It is the pathogen of human bronchitis and walking pneumonia, and named community-acquired pneumonia. In addition to severe respiratory symptoms, there are clinical extrapulmonary manifestations in the skin, brain, kidney, musculoskeletal, digestive system, and even blood system after M. pneumoniae infection. Hereby, we comprehensively summarized and reviewed the intrapulmonary and extrapulmonary pathogenesis of M. pneumoniae infection. The pathogenesis of related respiratory symptoms caused by M. pneumoniae is mainly adhesion damage, direct damage including nutrient predation, invasion and toxin, cytokine induced inflammation damage and immune evasion effect. The pathogenesis of extrapulmonary manifestations includes direct damage mediated by invasion and inflammatory factors, indirect damage caused by host immune response, and vascular occlusion. The intrapulmonary and extrapulmonary pathogenic mechanisms of M. pneumoniae infection are independent and interrelated, and have certain commonalities. In fact, the pathogenic mechanisms of M. pneumoniae are complicated, and the specific content is still not completely clear, further researches are necessary for determining the detailed pathogenesis of M. pneumoniae. This review can provide certain guidance for the effective prevention and treatment of M. pneumoniae infection.

Pathogenicity and virulence of Mycoplasma genitalium: Unraveling Ariadne's Thread

Mycoplasma genitalium, a pathogen from class Mollicutes, has been linked to sexually transmitted diseases and sparked widespread concern. To adapt to its environment, M. genitalium has evolved specific adhesins and motility mechanisms that allow it to adhere to and invade various eukaryotic cells, thereby causing severe damage to the cells. Even though traditional exotoxins have not been identified, secreted nucleases or membrane lipoproteins have been shown to cause cell death and inflammatory injury in M. genitalium infection. However, as both innate and adaptive immune responses are important for controlling infection, the immune responses that develop upon infection do not necessarily eliminate the organism completely. Antigenic variation, detoxifying enzymes, immunoglobulins, neutrophil extracellular trap-degrading enzymes, cell invasion, and biofilm formation are important factors that help the pathogen overcome the host defence and cause chronic infections in susceptible individuals. Furthermore, M. genitalium can increase the susceptibility to several sexually transmitted pathogens, which significantly complicates the persistence and chronicity of M. genitalium infection. This review aimed to discuss the virulence factors of M. genitalium to shed light on its complex pathogenicity and pathogenesis of the infection.

Genotyping and biofilm formation of Mycoplasma hyopneumoniae and their association with virulence

Mycoplasma hyopneumoniae, the causative agent of swine respiratory disease, demonstrates differences in virulence. However, factors associated with this variation remain unknown. We herein evaluated the association between differences in virulence and genotypes as well as phenotype (i.e., biofilm formation ability). Strains 168 L, RM48, XLW-2, and J show low virulence and strains 232, 7448, 7422, 168, NJ, and LH show high virulence, as determined through animal challenge experiments, complemented with in vitro tracheal mucosa infection tests. These 10 strains with known virulence were then subjected to classification via multilocus sequence typing (MLST) with three housekeeping genes, P146-based genotyping, and multilocus variable-number tandem-repeat analysis (MLVA) of 13 loci. MLST and P146-based genotyping identified 168, 168 L, NJ, and RM48 as the same type and clustered them in a single branch. MLVA assigned a different sequence type to each strain. Simpson’s index of diversity indicates a higher discriminatory ability for MLVA. However, no statistically significant correlation was found between genotypes and virulence. Furthermore, we investigated the correlation between virulence and biofilm formation ability. The strains showing high virulence demonstrate strong biofilm formation ability, while attenuated strains show low biofilm formation ability. Pearson correlation analysis revealed a significant positive correlation between biofilm formation ability and virulence. To conclude, there was no association between virulence and our genotyping data, but virulence was found to be significantly associated with the biofilm formation ability of M. hyopneumoniae.

Functional characterization of complement factor H in host defense against bacterial pathogen in Nile tilapia (Oreochromis niloticus)

Complement factor H (CFH), a multifunctional soluble complement regulatory protein, can bind to a variety of pathogens and play a crucial role in host innate immune defense. To explore the functional characteristics of CFH (OnCFH) in Nile tilapia (Oreochromis niloticus), we cloned and characterized the open reading frame (ORF) of OnCFH in this study. The full-length of OnCFH ORF is 1359 bp, encoding 452 aa for a 48.85 kDa peptide, and its predicted structure containing six short complement-like repeats (SCRs). The analysis of tissue distribution showed that OnCFH was constitutively expressed in all tested tissues, with the highest in the liver. Upon Streptococcus agalactiae and Aeromonas hydrophila stimuli in vivo and in vitro, OnCFH mRNA transcript was significantly upregulated in head kidney tissue as well as head kidney monocytes/macrophages. Further, the recombinant OnCFH protein ((r)OnCFH) could bind to pathogenic bacteria in a dose-dependent. Moreover, it got involved in the regulation of inflammation as well as phagocytosis of monocytes/macrophages. The knockdown of OnCFH remarkably decreased the amount of bacteria in the head kidney. In summary, our data demonstrated that OnCFH could participate in the immune response of Nile tilapia against bacterial infection.

Serum Resistance of Mycoplasma agalactiae Strains and Mutants Bearing Different Lipoprotein Profiles

In order to spread systemically, resistance against complement and other factors present in serum is an important trait in pathogenic bacteria. The variable proteins of Mycoplasma agalactiae (Vpmas) have been shown to affect differential adhesion, invasion and immune evasion, and undergo high-frequency phase-variation in expression. However, nothing is known about their involvement in M. agalactiae’s serum susceptibility. To evaluate this, the PG2 strain, the GM139 strain and the six Vpma phase-locked mutants (PLMs, PLMU to PLMZ) were tested for their ability to survive in the presence of non-sensitized and sensitized sheep serum, as well as guinea pig complement. Additionally, the reactivity of the sensitized sheep serum was analysed on the strains via western blotting. Overall data demonstrate PG2 strain to be more susceptible to sheep serum compared to the GM139 strain bearing a different Vpma profile. Significant differences were also observed between the different PLMs, with PLMU and PLMX showing the highest serum susceptibility in serum, while the other PLMs expressing longer Vpma proteins were more resistant. The results are in good correlation with previous studies where shorter lipoprotein variants contributed to a higher susceptibility to complement. Since none of the tested strains and PLMs were susceptible to non-sensitized sheep serum, antibodies seem to play an important role in serum killing.

Selection of internal reference gene for normalization of reverse transcription-quantitative polymerase chain reaction analysis in Mycoplasma hyopneumoniae

Mycoplasma hyopneumoniae is the etiological agent of swine enzootic pneumonia (EP), which resulting in considerable economic losses in pig farming globally. Reverse transcription-quantitative polymerase chain reaction (RT-qPCR) is a major tool for gene expression studies. However, no internal reference genes for normalization of RT-qPCR data of M. hyopneumoniae have been reported. The aim of this study was to screen the most stable genes for RT-qPCR analysis in M. hyopneumoniae under different conditions. Therefore, a total of 13 candidate internal reference genes (rpoC, Lipo, sgaB, oppB, hypo621, oppF, gyrB, uvrA, P146, prfA, proS, gatB, and hypo499) of M. hyopneumoniae filtered according to the reported quantitative proteomic analysis and the 16S rRNA internal reference gene frequently used in other bacteria were selected for RT-qPCR analysis. The mRNAs from different virulence strains (168, 168 L, J, NJ, and LH) at five different growth phases were extracted. The corresponding cycle threshold (Ct) values of the 25 reverse transcribed cDNAs using the 14 candidate genes were determined. Different internal reference genes or combinations were then screened for expression stability analysis using various statistical tools and algorithms, including geNorm, BestKeeper, and NormFinder software, to ensure the reliability of the analysis. Through further comprehensive evaluation of the RefFinder software, it is concluded that the gatB gene was the most suitable internal reference gene for samples of the different virulence strains in different growth phases for M. hyopneumoniae, followed by prfA, hypo499, and gyrB.

Extraintestinal pathogenic Escherichia coli utilizes the surface-expressed elongation factor Tu to bind and acquire iron from holo-transferrin

Extraintestinal pathogenic Escherichia coli (ExPEC) is a common anthropozoonotic pathogen that causes systemic infections. To establish infection, ExPEC must utilize essential nutrients including iron from the host. Transferrin is an important iron source for multiple bacteria. However, the mechanism by which ExPEC utilizes transferrin remains unclear. In this study, we found that iron-saturated holo-transferrin rather than iron-free apo-transferrin promoted the vitality of ExPEC in heat-inactivated human serum. The multifunctional protein Elongation factor Tu (EFTu) worked as a holo-transferrin binding protein. EFTu not only bound holo-transferrin rather than apo-transferrin but also released transferrin-related iron, with all domains of EFTu involved in holo-transferrin binding and iron release events. We also identified the surface location of EFTu on ExPEC. Overexpression of EFTu on the surface of nonpathogenic E. coli not only promoted the binding of bacteria to holo-transferrin but also facilitated the uptake of transferrin-related iron. More importantly, it significantly enhanced the survival of E. coli in heat-inactivated human serum, which was positively correlated with holo-transferrin but not apo-transferrin. Our research revealed a novel function of EFTu in binding holo-transferrin to promote iron uptake by bacteria, suggesting that EFTu was a potential virulence factor of ExPEC. In addition, our study provided research avenues into the iron acquisition and pathogenicity mechanisms of ExPEC.

DnaK Functions as a Moonlighting Protein on the Surface of Mycoplasma hyorhinis Cells

Mycoplasma hyorhinis is a common pathogen of swine and is also associated with various human tumors. It causes systemic inflammation, typically polyserositis and polyarthritis, in some infected pigs. However, the pathogenic mechanism of M. hyorhinis remains unclear. DnaK is a highly conserved protein belonging to the heat-shock protein 70 family of molecular chaperones, which plays important roles as a moonlighting protein in various bacteria. In the present study, we identified the surface exposure of M. hyorhinis DnaK. Two virulent strains expressed more DnaK on their surface than the avirulent strain. Thereafter, the potential moonlighting functions of DnaK were investigated. Recombinant M. hyorhinis DnaK (rMhr-DnaK) was found to be able to adhere to swine PK-15 cells and human NCI-H292 cells. It also bound to four extracellular matrix components-fibronectin, laminin, type IV collagen, and vitronectin-in a dose-dependent manner. ELISA demonstrated an interaction between rMhr-DnaK and plasminogen, which was significantly inhibited by a lysine analog, ε-aminocaproic acid. rMhr-DnaK-bound plasminogen was activated by tissue-type plasminogen activator (tPA), and the addition of rMhr-DnaK significantly enhanced the activation. Finally, a DnaK-specific antibody was detected in the serum of pigs immunized with inactivated vaccines, which indicated good immunogenicity of it. In summary, our findings imply that DnaK is an important multifunctional moonlighting protein in M. hyorhinis and likely participates extensively in the infection and pathogenesis processes of M. hyorhinis.

Group B Streptococcus Surface Protein β: Structural Characterization of a Complement Factor H-Binding Motif and Its Contribution to Immune Evasion

The β protein from group B Streptococcus (GBS) is a ∼132-kDa, cell-surface exposed molecule that binds to multiple host-derived ligands, including complement factor H (FH). Many details regarding this interaction and its significance to immune evasion by GBS remain unclear. In this study, we identified a three-helix bundle domain within the C-terminal half of the B75KN region of β as the major FH-binding determinant and determined its crystal structure at 2.5 Å resolution. Analysis of this structure suggested a role in FH binding for a loop region connecting helices α1 and α2, which we confirmed by mutagenesis and direct binding studies. Using a combination of protein cross-linking and mass spectrometry, we observed that B75KN bound to complement control protein (CCP)3 and CCP4 domains of FH. Although this binding site lies within a complement regulatory region of FH, we determined that FH bound by β retained its decay acceleration and cofactor activities. Heterologous expression of β by Lactococcus lactis resulted in recruitment of FH to the bacterial surface and a significant reduction of C3b deposition following exposure to human serum. Surprisingly, we found that FH binding by β was not required for bacterial resistance to phagocytosis by neutrophils or killing of bacteria by whole human blood. However, loss of the B75KN region significantly diminished bacterial survival in both assays. Although our results show that FH recruited to the bacterial surface through a high-affinity interaction maintains key complement-regulatory functions, they raise questions about the importance of FH binding to immune evasion by GBS as a whole.

The role of properdin and Factor H in disease

The complement system consists of three pathways (alternative, classical, and lectin) that play a fundamental role in immunity and homeostasis. The multifunctional role of the complement system includes direct lysis of pathogens, tagging pathogens for phagocytosis, promotion of inflammatory responses to control infection, regulation of adaptive cellular immune responses, and removal of apoptotic/dead cells and immune complexes from circulation. A tight regulation of the complement system is essential to avoid unwanted complement-mediated damage to the host. This regulation is ensured by a set of proteins called complement regulatory proteins. Deficiencies or malfunction of these regulatory proteins may lead to pro-thrombotic hematological diseases, renal and ocular diseases, and autoimmune diseases, among others. This review focuses on the importance of two complement regulatory proteins of the alternative pathway, Factor H and properdin, and their role in human diseases with an emphasis on: (a) characterizing the main mechanism of action of Factor H and properdin in regulating the complement system and protecting the host from complement-mediated attack, (b) describing the dysregulation of the alternative pathway as a result of deficiencies, or mutations, in Factor H and properdin, (c) outlining the clinical findings, management and treatment of diseases associated with mutations and deficiencies in Factor H, and (d) defining the unwanted and inadequate functioning of properdin in disease, through a discussion of various experimental research findings utilizing in vitro, mouse and human models.

Development of an indirect competitive enzyme linked immunosorbent assay for the quantitative detection of Mycoplasma hyopneumoniae during the vaccine production process

Inactivated Mycoplasma hyopneumoniae vaccine is used extensively to control M. hyopneumoniae infection worldwide. Quantification techniques are essential in the process of standardizing and validating vaccines. In this study, we developed and optimized an indirect competitive enzyme linked immunosorbent assay (ic-ELISA) for the rapid quantification of M. hyopneumoniae antigen during vaccine production. Briefly, whole M. hyopneumoniae antigen was coated onto microtiter plates, and a polyclonal antibody against M. hyopneumoniae recombinant elongation factor thermo unstable (EF-Tu) protein was prepared and added with the samples to be tested. The methods were optimized and showed significant reproducibility, with coefficients of variation of 4.01% and 6.14% for the intra-and inter-assays, respectively. Quantification of M. hyopneumoniae cultures at different growth stages using the ic-ELISA test showed a similar curve to that of the traditional color changing units (CCU) assay, with a delay in the time when the amount reached the peak and started to fall. In the inactivated vaccine production process, the cultures could be harvested later than that for the live vaccine, at about 12 h after the end of the logarithmic growth phase. Different batches of cultures were measured for their relative potency value compared with the in-house reference vaccine, which was used to determine whether the cultures met the antigen amount requirements for vaccine preparation. The curves of the CCU titer and ic-ELISA titer in the logarithmic phase correlated strongly and a linear regression equation was established to calculate the CCU values rapidly using the ic-ELISA results. In conclusion, an ic-ELISA method was established to rapidly assess the amount of antigen in an M. hyopneumoniae culture during the vaccine production process.

Pathogenicity & virulence of Mycoplasma hyopneumoniae

Mycoplasma hyopneumoniae: is the etiological agent of porcine enzootic pneumonia (EP), a disease that impacts the swine industry worldwide. Pathogen-induced damage, as well as the elicited host-response, contribute to disease. Here, we provide an overview of EP epidemiology, control and prevention, and a more in-depth review of M. hyopneumoniae pathogenicity determinants, highlighting some molecular mechanisms of pathogen-host interactions relevant for pathogenesis. Based on recent functional, immunological, and comparative “omics” results, we discuss the roles of many known or putative M. hyopneumoniae virulence factors, along with host molecules involved in EP. Moreover, the known molecular bases of pathogenicity mechanisms, including M. hyopneumoniae adhesion to host respiratory epithelium, protein secretion, cell damage, host microbicidal response and its modulation, and maintenance of M. hyopneumoniae homeostasis during infection are described. Recent findings regarding M. hyopneumoniae pathogenicity determinants also contribute to the development of novel diagnostic tests, vaccines, and treatments for EP.

OmpC, a novel factor H-binding surface protein, is dispensable for the adherence and virulence of Salmonella enterica serovar Typhimurium

Salmonella enterica serovar Typhimurium utilizes a series of strategies to evade host innate immune defenses, including the serum complement system. Many microbial pathogens have evolved the ability to bind the complement regulatory protein factor H (FH) through their surface factor H-binding proteins (FHBPs) to circumvent the complement-mediated bactericidal effect. However, the roles of FHBPs in Salmonella pathogenesis are not well understood. In this study, we demonstrated that the survival of S. Typhimurium in human serum was decreased in a time and concentration dependent manner. Pre-incubation with FH attenuated the sensitivity of S. Typhimurium strain χ3761 to complement-mediated serum killing, suggesting FH binding enhance survival in serum. We aimed to identify novel S. Typhimurium FHBPs and characterize their biological functions. Here, six potential FHBPs were identified by two-dimensional (2D)-Far-western blot, and three of them were further confirmed to bind FH by Far-western blot and dot blot. We found that deletion of ompC (ΔompC) significantly inhibited the survival of S. Typhimurium strain χ3761 in human serum. Our results indicated that the ompC mutation does not affect χ3761 adhesion to HeLa cells. Furthermore, a mice infection model showed that deletion of ompC had no significant effect on the histopathological lesions or viability compared with the wild-type strain χ3761. In summary, these results suggested that OmpC is an important FHBP, but not a critical virulence factor of S. Typhimurium.

Attenuation of Mycoplasma hyopneumoniae Strain ES-2 and Comparative Genomic Analysis of ES-2 and Its Attenuated Form ES-2L

Mycoplasma hyopneumoniae causes swine respiratory disease worldwide. Due to the difficulty of isolating and cultivating M. hyopneumoniae, very few attenuated strains have been successfully isolated, which hampers the development of attenuated vaccines. In order to produce an attenuated M. hyopneumoniae strain, we used the highly virulent M. hyopneumoniae strain ES-2, which was serially passaged in vitro 200 times to produce the attenuated strain ES-2L, and its virulence was evidenced to be low in an animal experiment. In order to elucidate the mechanisms underlying virulence attenuation, we performed whole-genome sequencing of both strains and conducted comparative genomic analyses of strain ES-2 and its attenuated form ES-2L. Strain ES-2L showed three large fragment deletion regions including a total of 18 deleted genes, compared with strain ES-2. Analysis of single-nucleotide polymorphisms (SNPs) and indels indicated that 22 dels were located in 19 predicted coding sequences. In addition to these indels, 348 single-nucleotide variations (SNVs) were identified between strains ES-2L and ES-2. These SNVs mapped to 99 genes where they appeared to induce amino acid substitutions and translation stops. The deleted genes and SNVs may be associated with decreased virulence of strain ES-2L. Our work provides a foundation for further examining virulence factors of M. hyopneumoniae and for the development of attenuated vaccines.

Hijacking Factor H for Complement Immune Evasion

The complement system is an essential player in innate and adaptive immunity. It consists of three pathways (alternative, classical, and lectin) that initiate either spontaneously (alternative) or in response to danger (all pathways). Complement leads to numerous outcomes detrimental to invaders, including direct killing by formation of the pore-forming membrane attack complex, recruitment of immune cells to sites of invasion, facilitation of phagocytosis, and enhancement of cellular immune responses. Pathogens must overcome the complement system to survive in the host. A common strategy used by pathogens to evade complement is hijacking host complement regulators. Complement regulators prevent attack of host cells and include a collection of membrane-bound and fluid phase proteins. Factor H (FH), a fluid phase complement regulatory protein, controls the alternative pathway (AP) both in the fluid phase of the human body and on cell surfaces. In order to prevent complement activation and amplification on host cells and tissues, FH recognizes host cell-specific polyanionic markers in combination with complement C3 fragments. FH suppresses AP complement-mediated attack by accelerating decay of convertases and by helping to inactivate C3 fragments on host cells. Pathogens, most of which do not have polyanionic markers, are not recognized by FH. Numerous pathogens, including certain bacteria, viruses, protozoa, helminths, and fungi, can recruit FH to protect themselves against host-mediated complement attack, using either specific receptors and/or molecular mimicry to appear more like a host cell. This review will explore pathogen complement evasion mechanisms involving FH recruitment with an emphasis on: (a) characterizing the structural properties and expression patterns of pathogen FH binding proteins, as well as other strategies used by pathogens to capture FH; (b) classifying domains of FH important in pathogen interaction; and (c) discussing existing and potential treatment strategies that target FH interactions with pathogens. Overall, many pathogens use FH to avoid complement attack and appreciating the commonalities across these diverse microorganisms deepens the understanding of complement in microbiology.