Envelope protein complexes of Mycobacterium avium subsp. paratuberculosis and their antigenicity

Vaccination of cattle with a virus vector vaccine against a major membrane protein of Mycobacterium avium subsp. paratuberculosis elicits CD8 cytotoxic T cells that kill intracellular bacteria

Analysis of the recall response ex vivo in cattle vaccinated with a Mycobacterium avium subsp. paratuberculosis (Map) rel deletion mutant revealed the immune response was directed toward a 35 kD major membrane protein (MMP) of Map. Antigen presenting cells (APC) primed with MMP elicited expansion of CD8 cytotoxic memory T cells (CTL) with ability to kill intracellular bacteria. Development of CTL was MHC-restricted. The gene MAP2121c, encoding MMP, was modified for expression of MMP (tPA-MMP-2mut) in a mammalian cell line to explore the potential of developing MMP as a vaccine. Ex vivo stimulation of PBMC, from Map free cattle, with APC primed with tPA-MMP-2mut expressed p35 elicited a primary CD8 CTL response comparable to the recall response elicited with PBMC from cattle vaccinated with either the Maprel deletion mutant or MMP. In the present study, the modified gene for MMP, now referred to as p35NN, was placed into a bovine herpes virus-4 (BoHV4) vector to determine the potential use of BoHV-4AΔTK-p35NN as a peptide-based vaccine. Subcutaneous vaccination of healthy cattle with BoHV-4AΔTK-p35NN elicited a CTL recall response, as detected ex vivo. The results show use of a virus vector is an effective way for delivery of MMP as a vaccine. The immunogenic activity of MMP was not lost when modified for expression in mammalian cells. The next step is to conduct a field trial to determine if presence of an immune response to MMP prevents Map from establishing an infection.

Proteomic profiling of membrane vesicles from Mycobacterium avium subsp. paratuberculosis: Navigating towards an insilico design of a multi-epitope vaccine targeting membrane vesicle proteins

Bacteria typically produce membrane vesicles (MVs) at varying levels depending on the surrounding environments. Gram-negative bacterial outer membrane vesicles (OMVs) have been extensively studied for over 30 years, but MVs from Gram-positive bacteria only recently have been a focus of research. In the present study, we isolated MVs from Mycobacterium avium subsp. paratuberculosis (MAP) and analyzed their protein composition using LC-MS/MS. A total of 316 overlapping proteins from two independent preparations were identified in our study, and topology prediction showed these cargo proteins have different subcellular localization patterns. When MVs were administered to bovine-derived macrophages, significant up-regulation of pro-inflammatory cytokines was observed via qRT-PCR. Proteome functional annotation revealed that many of these proteins are involved in the cellular protein metabolic process, tRNA aminoacylation, and ATP synthesis. Secretory proteins with high antigenicity and adhesion capability were mapped for B-cell and T-cell epitopes. Antigenic, Immunogenic and IFN-γ inducing B-cell, MHC-I, and MHC-II epitopes were stitched together through linkers to form multi-epitope vaccine (MEV) construct against MAP. Strong binding energy was observed during the docking of the 3D structure of the MEV with the bovine TLR2, suggesting that the putative MEV may be a promising vaccine candidate against MAP. However, in vitro and in vivo analysis is required to prove the immunogenic concept of the MEV which we will follow in our future studies. SIGNIFICANCE: Johne's disease is a chronic infection caused by Mycobacterium avium subsp. paratuberculosis that has a potential link to Crohn's disease in humans. The disease is characterized by persistent diarrhea and enteritis, resulting in significant economic losses due to reduced milk yield and premature culling of infected animals. The dairy industry in the United States alone experiences losses of approximately USD 250 million due to Johne's disease. The current vaccine against Johne's disease is limited by several factors, including variable efficacy, limited duration of protection, interference with diagnostic tests, inability to prevent infection, and logistical and cost-related challenges. Nevertheless, a multiepitope vaccine design approach targeting M. avium subsp. paratuberculosis has the potential to overcome these challenges and offer improved protection against Johne's disease.

Cryo-EM structure of Mycobacterium smegmatis DyP-loaded encapsulin

Encapsulins containing dye-decolorizing peroxidase (DyP)-type peroxidases are ubiquitous among prokaryotes, protecting cells against oxidative stress. However, little is known about how they interact and function. Here, we have isolated a native cargo-packaging encapsulin from Mycobacterium smegmatis and determined its complete high-resolution structure by cryogenic electron microscopy (cryo-EM). This encapsulin comprises an icosahedral shell and a dodecameric DyP cargo. The dodecameric DyP consists of two hexamers with a twofold axis of symmetry and stretches across the interior of the encapsulin. Our results reveal that the encapsulin shell plays a role in stabilizing the dodecameric DyP. Furthermore, we have proposed a potential mechanism for removing the hydrogen peroxide based on the structural features. Our study also suggests that the DyP is the primary cargo protein of mycobacterial encapsulins and is a potential target for antituberculosis drug discovery.

Discovery and characterization of a novel family of prokaryotic nanocompartments involved in sulfur metabolism

Prokaryotic nanocompartments, also known as encapsulins, are a recently discovered proteinaceous organelle-like compartment in prokaryotes that compartmentalize cargo enzymes. While initial studies have begun to elucidate the structure and physiological roles of encapsulins, bioinformatic evidence suggests that a great diversity of encapsulin nanocompartments remains unexplored. Here, we describe a novel encapsulin in the freshwater cyanobacterium Synechococcus elongatus PCC 7942. This nanocompartment is upregulated upon sulfate starvation and encapsulates a cysteine desulfurase enzyme via an N-terminal targeting sequence. Using cryo-electron microscopy, we have determined the structure of the nanocompartment complex to 2.2 Å resolution. Lastly, biochemical characterization of the complex demonstrated that the activity of the cysteine desulfurase is enhanced upon encapsulation. Taken together, our discovery, structural analysis, and enzymatic characterization of this prokaryotic nanocompartment provide a foundation for future studies seeking to understand the physiological role of this encapsulin in various bacteria.

Interferon-γ Response of Mycobacterium avium subsp. paratuberculosis Infected Goats to Recombinant and Synthetic Mycobacterial Antigens

Despite its potential for early diagnosis of Mycobacterium avium subsp. paratuberculosis (MAP) infection, the IFN-γ release assay is not used routinely, because of low specificity of the established crude antigen preparation Johnin (PPDj). Limited data are available assessing the potential of MAP-derived protein and lipopeptide antigens to replace PPDj in assays for goats, while cattle and sheep have been studied more extensively. Furthermore, MAP infection is claimed to interfere with the diagnosis of bovine tuberculosis when other crude antigen preparations (PPDb, PPDa) are applied. In this study, the diagnostic potential of MAP-derived recombinant protein antigens, synthetic MAP lipopentapeptides and of Mycobacterium bovis-specific peptide cocktails was assessed compared to crude mycobacterial antigen preparations in experimentally infected goats. Goats were inoculated with MAP, or Mycobacterium avium subsp. hominissuis (MAH) as surrogate for environmental mycobacteria, non-exposed animals served as controls. Mycobacterium avium Complex-specific antibody and PPDj-induced IFN-γ responses were monitored in vivo. Infection status was assessed by pathomorphological findings and bacteriological tissue culture at necropsy 1 year after inoculation. The IFN-γ response to 13 recombinant protein antigens of MAP, two synthetic MAP lipopentapeptides and three recombinant peptide cocktails of Mycobacterium bovis was investigated at three defined time points after infection. At necropsy, MAP or MAH infection was confirmed in all inoculated goats, no signs of infection were found in the controls. Antibody formation was first detected 3-6 weeks post infection (wpi) in MAH-inoculated and 11-14 wpi in the MAP-inoculated goats. Maximum PPDj-induced IFN-γ levels in MAH and MAP exposed animals were recorded 3-6 and 23-26 wpi, respectively. Positive responses continued with large individual variation. Antigens Map 0210c, Map 1693c, Map 2020, Map 3651cT(it), and Map 3651c stimulated increased whole blood IFN-γ levels in several MAP-inoculated goats compared to MAH inoculated and control animals. These IFN-γ levels correlated with the intensity of the PPDj-induced responses. The two synthetic lipopentapeptides and the other MAP-derived protein antigens had no discriminatory potential. Stimulation with Mycobacterium bovis peptide cocktails ESAT6-CFP10, Rv3020c, and Rv3615c did not elicit IFN-γ production. Further work is required to investigate if test sensitivity will increase when mixtures of the MAP-derived protein antigens are applied.

Simultaneous cognate epitope recognition by bovine CD4 and CD8 T cells is essential for primary expansion of antigen-specific cytotoxic T-cells following ex vivo stimulation with a candidate Mycobacterium avium subsp. paratuberculosis peptide vaccine

Studies in cattle show CD8 cytotoxic T cells (CTL), with the ability to kill intracellular bacteria, develop following stimulation of monocyte-depleted peripheral blood mononuclear cells (mdPBMC) with antigen presenting cells (APC, i.e. conventional dendritic cells [cDC] and monocyte-derived DC [MoDC]) pulsed with MMP, a membrane protein from Mycobacterium avium subsp. paratuberculosis (Map) encoded by MAP2121c. CTL activity was diminished if CD4 T cells were depleted from mdPBMC before antigen (Ag) presentation by APC, suggesting simultaneous cognate recognition of MMP epitopes presented by MHC I and MHC II molecules to CD4 and CD8 T cells is essential for development of CTL activity. To explore this possibility, studies were conducted with mdPBMC cultures in the presence of monoclonal antibodies (mAbs) specific for MHC class I and MHC class II molecules. The CTL response of mdPBMC to MMP-pulsed APC was completely blocked in the presence of mAbs to both MHC I and II molecules and also blocked in the presence of mAbs to either MHC I or MHC II alone. The results demonstrate simultaneous cognate recognition of Ag by CD4 and CD8 T cells is essential for delivery of CD4 T cell help to CD8 T cells to elicit development of CTL.

Capacity to Elicit Cytotoxic CD8 T Cell Activity Against Mycobacterium avium subsp. paratuberculosis Is Retained in a Vaccine Candidate 35 kDa Peptide Modified for Expression in Mammalian Cells

Studies focused on development of an attenuated vaccine against Mycobacterium avium subsp. paratuberculosis (Map), the causative agent of paratuberculosis (Ptb) in cattle and other species, revealed that deletion of relA, a global gene regulator, abrogates the ability of Map to establish a persistent infection. In the absence of relA, cattle develop CD8 cytotoxic T cells (CTL) with the ability to kill intracellular bacteria. Analysis of the recall response to a relA mutant, Map/ΔrelA, with cells from a vaccinated steer demonstrated that a 35-kDa membrane peptide (MMP) is one of the targets of the response. This observation suggested that it might be possible to develop a peptide-based vaccine. As reported here, the gene encoding the hypothetical MMP ORF, MAP2121c, was modified for expression in mammalian cells as a first step in developing an expression cassette for incorporation into a mammalian expression vector. The modified sequence of MMP, tPA-MMP, was mutated to generate two additional sequences for the study, one with substitutions to replace five potential residues that could be glycosylated, tPA-MMP-5mut, and one with substitutions to replace the first two potential residues that could be glycosylated, tPA-MMP-2mut. The sequences were placed in an expression cassette to produce peptides for analysis. An ex vivo platform was used with flow cytometry and a bacterium viability assay to determine if modifications in the gene encoding MMP for expression in mammalian cells altered its capacity to elicit development of CD8 CTL, essential for its use in a peptide-based vaccine. Monocyte-depleted PBMC (mdPBMC) were stimulated with antigen-presenting cells (APC) pulsed with different MMP constructs. CD4 and CD8 T cells proliferated in response to stimulation with MMP (control) expressed in Escherichia coli (eMMP), tPA-MMP, and tPA-MMP-2mut. CD8 T cells retained the capacity to kill intracellular bacteria. The tPA-MMP-5mut failed to elicit a proliferative response and was not included in further studies. The data show that the expression cassettes containing MMP and MMP-2mut can be used to screen and select a mammalian expression vector for the development of an efficacious peptide-based vaccine against Ptb.

An update on Mycobacterium avium subspecies paratuberculosis antigens and their role in the diagnosis of Johne's disease

Mycobacterium avium subsp. paratuberculosis (MAP) is responsible for Johne's disease (JD) or paratuberculosis. Diagnosis of MAP infection by measuring host cell-mediated and humoral immune responses has been a major focus in MAP research. For this purpose, several MAP antigens such as secreted protein, cell envelope protein, cell-mediated immune and lipoprotein antigens have been identified and tested to measure their diagnostic utility with varying degree of success. Identifying the optimal antigen or antigen combinations for diagnosis of infected animals is hindered by the complex nature of the disease, prolonged subclinical infection, the differential expression of antigens and scarcity of well characterized MAP-specific epitopes making selection of a single MAP antigen very difficult. Thus, multiplexing of antigens with larger scale and longitudinal studies may lead to development of cost-effective next generation serodiagnostics. This mini review focuses on the role of different MAP antigens in the diagnosis of JD.

Early IgG2 in calves experimentally infected with Mycobacterium avium subsp. paratuberculosis

The diagnosis of the early stages of paratuberculosis, caused by Mycobacterium avium subsp. paratuberculosis (Map), is a cumbersome task. In this study, an experimental Map-infection model of calves was used to improve the knowledge of early antibody response and to evaluate different in-house ELISAs in the detection of subclinical paratuberculosis. Calves were challenged with Map strain _IS900-RFLPA (n = 3) or Map strain _IS900-RFLPC (n = 2) (Argentinean isolated strains) or mock infected (n = 3), and their specific humoral response was evaluated. The diagnostic ELISA (IgG against Map protoplasmic antigen; PPA) could not detect the infection throughout the experimental period (180 days post-infection; dpi), whereas the IgG2/PPA-ELISA was able to identify infected calves at least once during the experiment. In addition, the use of crude Map extract detected most of the infections from 60 dpi onwards. Antibodies were also characterized by immunoblot: IgG2-reactivity to antigens of molecular weight lower than 50 kDa was detected in all infected calves. The experimental Map-infection model of calves used allows the study of the early humoral immune response in paratuberculosis. The evaluation of IgG2 specific to antigens lighter than 50 kDa emerges as an interesting alternative in calves naturally infected with paratuberculosis.

A peptide-based vaccine for Mycobacterium avium subspecies paratuberculosis

Recent efforts to develop a live attenuated vaccine against Mycobacterium avium subsp. paratuberculosis (Map), the causative agent of Johne's disease (JD), revealed relA is important in Map virulence. Deletion of the relA gene impairs the ability of Map to establish a persistent infection. Analysis of the basis for this observation revealed infection with a relA deletion mutant (ΔrelA) elicits development of cytotoxic CD8 T cells (CTL) with the ability to kill intracellular bacteria. Further analysis of the recall response elicited by ΔrelA vaccination showed a 35 kDa membrane peptide (MMP) is one of the targets of the immune response, suggesting it might be possible to develop a peptide-based vaccine based on MMP. To explore this possibility, ex vivo vaccination studies were conducted with MMP alone and incorporated into a nanoparticle (NP) vector comprised of poly (D, L-lactide-co-glycolide) and monophosphoryl lipid A (PLGA/MPLA). As reported, ex vivo vaccination studies showed CD8 CTL were elicited with classic and monocyte derived dendritic cells (cDC and MoDC) pulsed with MMP alone and incorporated into a PGLA/MPLA vector. Incorporation of MMP into a NP vector enhanced the ability of CD8 CTL to kill intracellular bacteria. The findings indicate incorporation of MMP into a PGLA/MPLA nanoparticle vector is one of the possible ways to develop a MMP based vaccine for Johne's disease.

Identification of antigenic proteins from Mycobacterium avium subspecies paratuberculosis cell envelope by comparative proteomic analysis

Johne's disease (JD) is a contagious, chronic granulomatous enteritis of ruminants caused by Mycobacterium avium subsp. paratuberculosis (MAP). The aim of this study was to identify antigenic proteins from the MAP cell envelope (i.e. cell wall and cytoplasmic membranes) by comparing MAP, M. avium subsp. hominissuis (MAH) and M. smegmatis (MS) cell envelope protein profiles using a proteomic approach. Composite two-dimensional (2D) difference gel electrophoresis images revealed 13 spots present only in the image of the MAP cell envelope proteins. Using serum from MAP-infected cattle, immunoblot analysis of 2D gels revealed that proteins in the 13 spots were antigenic. These proteins were identified by liquid chromatography tandem mass spectrometry as products of the following genes: sdhA, fadE25_2, mkl, citA, gapdh, fadE3_2, moxR1, mmp, purC, mdh, atpG, fbpB and desA2 as well as two proteins without gene names identified as transcriptional regulator (MAP0035) protein and hypothetical protein (MAP1233). Protein functions ranged from energy generation, cell wall biosynthesis, protein maturation, bacterial replication and invasion of epithelial cells, functions considered essential to MAP virulence and intracellular survival. Five MAP cell envelope proteins, i.e. SdhA, FadE25_2, FadE3_2, MAP0035 and DesA2 were recombinantly expressed, three of which, i.e. SdhA, FadE25_2 and DesA2, were of sufficient purity and yield to generate polyclonal antibodies. Immunoblot analysis revealed antibodies reacted specifically to the respective MAP cell envelope proteins with minimal cross-reactivity with MAH and MS cell envelope proteins. Identification and characterization of MAP-specific proteins and antibodies to those proteins may be useful in developing new diagnostic tests for JD diagnosis.

Early detection of Mycobacterium avium subsp. paratuberculosis infection in cattle with multiplex-bead based immunoassays

Johne’s Disease (JD), caused by Mycobacterium avium subspecies paratuberculosis (MAP), results in significant economic loss to livestock production. The early detection of MAP infection in animals with extant serological assays has remained challenging due to the low sensitivity of commercially available ELISA tests, a fact that has hampered the development of effective JD control programs. Our recent protein microarray-based studies identified several promising candidate antigens that are immunogenic during different stages of MAP infection. To evaluate these antigens for use in diagnostic assays and reliably identify animals with MAP infection, a multiplex (Luminex^®) assay was developed using color-coded flourescent beads coupled to 6 MAP recombinant proteins and applied to screen 180 serum and 90 milk samples from cows at different stages of MAP infection including negative (NL), fecal test positive/ELISA negative (F+E-), and fecal positive/ELISA positive (F+E+). The results show that while serum antibody reactivities to each of the 6 antigens were highest in F+E+ group, antibody reactivity to three of the six antigens were identified in the F+E- group, suggesting that these three antigens are expressed and provoke antibody responses during the early infection stages with MAP. Further, antibodies against all six antigens were elevated in milk samples from both the F+E- and F+E+ groups in comparison to the NL group (p<0.01). Taken together, the results of our investigation suggest that multiplex bead-based assays are able to reliably identify MAP infection, even during early stages when antibody responses in animals are undetectable with widely used commercial ELISA tests.

Knowledge gaps that hamper prevention and control of Mycobacterium avium subspecies paratuberculosis infection

In the last decades, many regional and country-wide control programmes for Johne's disease (JD) were developed due to associated economic losses, or because of a possible association with Crohn's disease. These control programmes were often not successful, partly because management protocols were not followed, including the introduction of infected replacement cattle, because tests to identify infected animals were unreliable, and uptake by farmers was not high enough because of a perceived low return on investment. In the absence of a cure or effective commercial vaccines, control of JD is currently primarily based on herd management strategies to avoid infection of cattle and restrict within-farm and farm-to-farm transmission. Although JD control programmes have been implemented in most developed countries, lessons learned from JD prevention and control programmes are underreported. Also, JD control programmes are typically evaluated in a limited number of herds and the duration of the study is less than 5 year, making it difficult to adequately assess the efficacy of control programmes. In this manuscript, we identify the most important gaps in knowledge hampering JD prevention and control programmes, including vaccination and diagnostics. Secondly, we discuss directions that research should take to address those knowledge gaps.

Identification of Novel Seroreactive Antigens in Johne's Disease Cattle by Using the Mycobacterium tuberculosis Protein Array

Johne's disease, a chronic gastrointestinal inflammatory disease caused by Mycobacterium avium subspecies paratuberculosis, is endemic in dairy cattle and other ruminants worldwide and remains a challenge to diagnose using traditional serological methods. Given the close phylogenetic relationship between M. avium subsp. paratuberculosis and the human pathogen Mycobacterium tuberculosis, here, we applied a whole-proteome M. tuberculosis protein array to identify seroreactive and diagnostic M. avium subsp. paratuberculosis antigens. A genome-scale pairwise analysis of amino acid identity levels between orthologous proteins in M. avium subsp. paratuberculosis and M. tuberculosis showed an average of 62% identity, with more than half the orthologous proteins sharing >75% identity. Analysis of the M. tuberculosis protein array probed with sera from M. avium subsp. paratuberculosis-infected cattle showed antibody binding to 729 M. tuberculosis proteins, with 58% of them having ≥70% identity to M. avium subsp. paratuberculosis orthologs. The results showed that only 4 of the top 40 seroreactive M. tuberculosis antigens were orthologs of previously reported M. avium subsp. paratuberculosis antigens, revealing the existence of a large number of previously unrecognized candidate diagnostic antigens. Enzyme-linked immunosorbent assay (ELISA) testing of 20 M. avium subsp. paratuberculosis recombinant proteins, representing reactive and nonreactive M. tuberculosis orthologs, further confirmed that the M. tuberculosis array has utility as a screening tool for identifying candidate antigens for Johne's disease diagnostics. Additional ELISA testing of field serum samples collected from dairy herds around the United States revealed that MAP2942c had the strongest seroreactivity with Johne's disease-positive samples. Collectively, our studies have considerably expanded the number of candidate M. avium subsp. paratuberculosis proteins with potential utility in the next generation of rationally designed Johne's disease diagnostic assays.

Inferring biomarkers for Mycobacterium avium subsp. paratuberculosis infection and disease progression in cattle using experimental data

Available diagnostic assays for Mycobacterium avium subsp. paratuberculosis (MAP) have poor sensitivities and cannot detect early stages of infection, therefore, there is need to find new diagnostic markers for early infection detection and disease stages. We analyzed longitudinal IFN-γ, ELISA-antibody and fecal shedding experimental sensitivity scores for MAP infection detection and disease progression. We used both statistical methods and dynamic mathematical models to (i) evaluate the empirical assays (ii) infer and explain biological mechanisms that affect the time evolution of the biomarkers, and (iii) predict disease stages of 57 animals that were naturally infected with MAP. This analysis confirms that the fecal test is the best marker for disease progression and illustrates that Th1/Th2 (IFN-γ/ELISA antibodies) assays are important for infection detection, but cannot reliably predict persistent infections. Our results show that the theoretical simulated macrophage-based assay is a potential good diagnostic marker for MAP persistent infections and predictor of disease specific stages. We therefore recommend specifically designed experiments to test the use of a based assay in the diagnosis of MAP infections.

Composition and Potency Characterization of Mycobacterium avium subsp. paratuberculosis Purified Protein Derivatives

Mycobacterium avium subsp. paratuberculosis (MAP) purified protein derivatives (PPDs) are immunologic reagents prepared from cultured filtrates of the type strain. Traditional production consists of floating culture incubation at 37°C, organism inactivation by autoclaving, coarse filtration, and protein precipitation. Three traditional production PPDs were used in this study including lot 9801, which served as a reference and has been used in the field for decades. Alternative production PPDs (0902A and 0902B), in which the autoclaving step was removed, were also analyzed in this study. SDS-PAGE analysis revealed protein smearing in traditional PPDs, but distinct bands were observed in the alternative PPD preparations. Antibody bound distinct protein bands in the alternative PPDs by immunoblot analysis, whereas an immunoreactive smear was observed with the traditional PPDs. Mass spectrometry identified 194 proteins among three PPD lots representing the two different production methods, ten of which were present in all PPDs examined. Selected proteins identified by mass spectrometry were recombinantly expressed and purified from E. coli and evaluated by the guinea pig potency test. Seven recombinant proteins showed greater erythema as compared to the reference PPD lot 9801 in paired guinea pigs and were able to stimulate interferon-gamma production in blood from Johne’s positive animals. These results suggest that autoclaving culture suspensions is not a necessary step in PPD production and specific proteins could supplant the PPD antigen for intradermal skin testing procedures and for use as in-vitro assay reagents.

Hygiene and Sanitation in Biogas Plants

The increasing number of agricultural biogas plants and higher amounts of digestate spread on agricultural land arouse a considerable interest in the hygiene situation of digested products. This chapter reviews the current knowledge on sanitation during anaerobic digestion and the hygienic status of digestate concerning a multitude of pathogens potentially compromising the health of humans, animals and plants. Physical, chemical and biological parameters influencing the efficiency of sanitation in anaerobic digestion are considered. The degree of germ reduction depends particularly on the resistance of the pathogen of concern, the processing conditions, the feedstock composition and the diligence of the operation management. Most scientific studies facing sanitation in biogas plants have provided data ascertaining reduction of pathogens by the biogas process. Some pathogens, however, are able to persist virtually unaffected due to the ability to build resistant permanent forms. As compared to the feedstock, the sanitary status of the digestate is thus improved or in the worst case, the sanitary quality remains almost unchanged. According to this, the spreading of digestate on agricultural area in accordance to current rules and best practice recommendations is considered to impose no additional risk for the health of humans, animals and plants.