Effect of Hesperidin on Barrier Function and Reactive Oxygen Species Production in an Oral Epithelial Cell Model, and on Secretion of Macrophage-Derived Inflammatory Mediators during Porphyromonas gingivalis Infection.

Porphyromonas gingivalis is a periodontopathogenic bacterium that can adhere to and colonize periodontal tissues, leading to an inflammatory process, and, consequently, tissue destruction. New therapies using flavonoids, such as hesperidin, are being studied, and their promising properties have been highlighted. The aim of this study was to evaluate the effect of hesperidin on the epithelial barrier function, reactive oxygen species (ROS) production, and on the inflammatory response caused by P. gingivalis in in vitro models. The integrity of the epithelial tight junctions challenged by P. gingivalis was determined by monitoring the transepithelial electrical resistance (TER). P. gingivalis adherence to a gingival keratinocyte monolayer and a basement membrane model were evaluated by a fluorescence assay. A fluorometric assay was used to determine the ROS production in gingival keratinocytes. The level of pro-inflammatory cytokines and matrix metalloproteinases (MMPs) secretion was evaluated by ELISA; to assess NF-κB activation, the U937-3xjB-LUC monocyte cell line transfected with a luciferase reporter gene was used. Hesperidin protected against gingival epithelial barrier dysfunction caused by P. gingivalis and reduced the adherence of P. gingivalis to the basement membrane model. Hesperidin dose-dependently inhibited P. gingivalis-mediated ROS production by oral epithelial cells as well as the secretion of IL-1ß, TNF-α, IL-8, MMP-2, and MMP-9 by macrophages challenged with P. gingivalis. Additionally, it was able to attenuate NF-κB activation in macrophages stimulated with P. gingivalis. These findings suggest that hesperidin has a protective effect on the epithelial barrier function, in addition to reducing ROS production and attenuating the inflammatory response associated with periodontal disease.

Paeoniflorin combined with norfloxacin ameliorates drug-resistant Streptococcus suis infection.

BACKGROUND: The increased resistance of bacterial pathogens to fluoroquinolones (FQs), such as norfloxacin and ciprofloxacin, supports the need to develop new antibacterial drugs and combination therapies using conventional antibiotics. The LuxS/AI-2 quorum sensing (QS) system can regulate the complex group behaviour of Streptococcus suis and impact its susceptibility to FQs. OBJECTIVES: We investigated the combination of paeoniflorin and norfloxacin as a novel and effective strategy against FQ-resistant S. suis. METHODS: FIC, AI-2 activity assay, real-time RT-PCR and biofilm inhibition assays were performed to investigate the in vitro effect of paeoniflorin combined with norfloxacin. Mouse protection and mouse anti-infection assays were performed to investigate the in vivo effect of paeoniflorin combined with norfloxacin. RESULTS: FIC results showed that paeoniflorin and norfloxacin exert a synergistic bactericidal effect. Evidence was brought that paeoniflorin reduces the S. suis AI-2 activity and significantly down-regulates the transcription of the FQ efflux pump gene. In addition, paeoniflorin can inhibit biofilm formation, thereby promoting the ability of norfloxacin to kill S. suis. Finally, we showed in a mouse model that paeoniflorin in association with norfloxacin is effective to treat S. suis infections. CONCLUSIONS: This study highlighted the inhibitory potential of paeoniflorin on the LuxS/AI-2 QS system of S. suis, and provided evidence that it can inhibit the FQ efflux pump and prevent biofilm formation to cooperate with norfloxacin in the treatment of resistant S. suis-related infections.

Production of TNF-𝛼 by macrophages stimulated with endodontic pathogens and its effect on the biological properties of stem cells of the apical papilla.

OBJECTIVES: The first objective of the present study was to investigate TNF-𝛼 secretion by macrophages stimulated with endodontic pathogens and bacterial cell surface components. The second objective was to assess the in vitro effects of TNF-𝛼 on periostin, cytokine, and matrix metalloproteinase (MMP) secretion by and the viability, proliferation rate, and mineralization potential of stem cells of the apical papilla (SCAP). METHODS: TNF-𝛼 secretion by macrophages stimulated with either endodontic pathogens or bacterial surface components was assessed using an enzyme-linked immunosorbent assay (ELISA). The viability and proliferation rate of SCAP treated with TNF-𝛼 were assessed using a colorimetric MTT assay. The mineralization potential of TNF-𝛼-treated SCAP was determined by Alizarin Red staining. Periostin secretion by SCAP was determined by ELISA while cytokine and MMP secretion were assessed using a multiplexing laser bead assay. RESULTS: TNF-𝛼 secretion by macrophages increased following a stimulation with Gram-negative and Gram-positive endodontic pathogens. Lipopolysaccharide and lipoteichoic acid also dose-dependently increased the secretion of TNF-𝛼 by macrophages. The viability, proliferation rate, and mineralization activity of SCAP were negatively affected by a TNF-𝛼 treatment. Treating SCAP with TNF-𝛼 attenuated the secretion of periostin and upregulated the secretion of several cytokines and MMPs. CONCLUSIONS: TNF-𝛼 exerts deleterious effects on SCAP by affecting their viability, proliferation rate, and mineralization potential. By its ability to induce the secretion of pro-inflammatory cytokines and MMPs by SCAP, TNF-𝛼 can contribute to creating an inflammatory environment, promoting tissue destruction, and consequently interfering with the success of regenerative endodontic therapy. CLINICAL RELEVANCE: TNF-𝛼 has deleterious impacts on stem cells of the apical papilla and may compromise the outcome of regenerative endodontic therapy.

Streptococcus suis suilysin compromises the function of a porcine tracheal epithelial barrier model.

Streptococcus suis is a bacterial pathogen that mainly colonizes the upper respiratory tract of pigs. It is known to cause severe infections such as septicemia, meningitis, arthritis, and endocarditis in pigs and to be responsible for major economic losses in the swine industry worldwide. To better understand the interactions between S. suis and the porcine respiratory epithelium, we investigated the ability of this pathogen to cause damage to the tracheal epithelial barrier. We showed that S. suis compromises the integrity of a tracheal epithelial barrier model as determined by measuring transepithelial electrical resistance and paracellular flux of FITC-dextran. As a consequence of this breakdown, S. suis translocates across the epithelial cell monolayer. On the other hand, a S. suis mutant deficient in the production of suilysin, a cholesterol-dependent cytolysin, was significantly impaired in its ability to cause damage to the epithelial barrier. In addition, a recombinant suilysin disrupted the integrity of the tracheal epithelial barrier. Immunofluorescence staining suggested that suilysin affects two major tight junction proteins (occludin and zonula occludens-1). In summary, S. suis is able to compromise the function of the porcine respiratory epithelial barrier through the action of suilysin. This better knowledge of the interactions between S. suis and tracheal epithelial cells may help in the development of novel strategies to prevent the invasion of the epithelium by this and other swine respiratory pathogens.

Preventing Candida albicans biofilm formation using aromatic-rich piperazines.

The global increase in microbial resistance is an imminent threat to public health. Effective treatment of infectious diseases now requires new antimicrobial therapies. We report herein the discovery of aromatic-rich piperazines that inhibit biofilm formation by C. albicans. 22 piperazines, including 16 novel ones, were prepared efficiently using a combination of solid- and solution phase synthesis. The most potent compound prevents morphological switching under several hypha-inducing conditions and reduces C. albicans' ability to adhere to epithelial cells. These processes are essential to the development of Candida biofilms, which are associated with its increased resistance to immune defenses and antifungal agents.

Antibiotic resistance related to biofilm formation in Streptococcus suis.

Streptococcus suis (S. suis) is an important zoonotic agent, which seriously impacts the pig industry and human health in various countries. Biofilm formation is likely contributing to the virulence and drug resistance in S. suis. A better knowledge of biofilm formation as well as to biofilm-dependent drug resistance mechanisms in S. suis can be of great significance for the prevention and treatment of S. suis infections. This literature review updates the latest scientific data related to biofilm formation in S. suis and its impact on drug tolerance and resistance.Key points• Biofilm formation is the important reasons for drug resistance of SS infections.• The review includes the regulatory mechanism of SS biofilm formation.• The review includes the drug resistance mechanisms of SS biofilm.

Tart cherry (Prunus cerasus L.) fractions inhibit biofilm formation and adherence properties of oral pathogens and enhance oral epithelial barrier function.

Dental caries, candidiasis, and periodontal disease are the most common oral infections affecting a wide range of the population worldwide. The present study investigated the effects of two tart cherry (Prunus cerasus L.) fractions on important oral pathogens, including Candida albicans, Streptococcus mutans, and Fusobacterium nucleatum, as well as on the barrier function of oral epithelial cells. Procyanidins and quercetin and its derivatives were the most important constituents found in the tart cherry fractions. Although the fractions showed poor antimicrobial activity, they inhibited biofilm formation by the three oral pathogens in a dose-dependent manner. The tart cherry fractions also attenuated the adherence of C. albicans and S. mutans to a hydroxylapatite surface as well as the adherence of F. nucleatum to oral epithelial cells. Treating oral epithelial cells with the tart cherry fractions significantly enhanced the barrier function as determined by monitoring the transepithelial electrical resistance. In conclusion, this study showed that the tart cherry fractions and their bioactive constituents could be promising antiplaque compounds by targeting biofilm formation and adherence properties of oral pathogens. Furthermore, its property of increasing the epithelial barrier function may protect against microbial invasion of the underlying connective tissue.

Highbush blueberry proanthocyanidins alleviate Porphyromonas gingivalis-induced deleterious effects on oral mucosal cells.

Strong evidence points to Porphyromonas gingivalis, a Gram-negative anaerobic bacterium, as a keystone species in the development of the chronic form of periodontitis. The aim of the present study was to investigate the ability of highbush blueberry proanthocyanidins (PACs) to alleviate the P. gingivalis-induced deleterious effects on oral mucosal cells. We first showed that highbush blueberry PACs protect the integrity of the gingival keratinocyte barrier against P. gingivalis-mediated damage, as determined by measuring the transepithelial electrical resistance and paracellular flux of FITC-conjugated dextran. Moreover, the PACs prevented the translocation of P. gingivalis across the gingival keratinocyte barrier model. The proteinase activity of P. gingivalis was inhibited by the PACs suggesting that they may exert beneficial effects by reducing proteolytic degradation of the epithelial tight junctions. Regulation of gingival fibroblast inflammatory reactions may be one of the ways to prevent and control periodontal disease progression and severity. We showed that PACs significantly reduce IL-6 and IL-8 secretion by P. gingivalis-stimulated gingival fibroblasts. The present study showed the capacity of highbush blueberry PACs to protect the integrity of an in vitro model of gingival keratinocyte barrier against P. gingivalis, and to attenuate the secretion of pro-inflammatory cytokines by gingival fibroblasts infected with P. gingivalis. These results suggest beneficial effects of blueberry PACs thus supporting the need for future clinical trials on the potential of these bioactive molecules for periodontal disease prevention and/or treatment.

Antibacterial and anti-inflammatory activities of cardamom (Elettaria cardamomum) extracts: Potential therapeutic benefits for periodontal infections.

Cardamom (Elettaria cardamomum) is a traditional aromatic plant for which several pharmacological properties have been associated. In this study, the antibacterial activity of two cardamom extracts (fruit and seeds), rich in volatile compounds, against major periodontal pathogens was evaluated. Moreover, the ability of the extracts to exert anti-inflammatory activity was tested. Both cardamom fruit and seed extracts exerted an antibacterial effect against Aggregatibacter actinomycetemcomitans, Fusobacterium nucleatum, Porphyromonas gingivalis, and Prevotella intermedia (minimum inhibitory concentrations: 0.5% [v/v], 0.25%, 0.062%, 0.125%, respectively and minimum bactericidal concentrations: 1%, 0.25%, 0.062%, 0.25%, respectively). The cell membrane of P. gingivalis was disrupted by a treatment with cardamom extracts suggesting the bactericidal mode of action. The extracts also inhibited biofilm formation although it correlated with a growth reduction. Moreover, the cardamom extracts significantly decreased the secretion of IL-1ß, TNF-α, and IL-8 by lipopolysaccharide-stimulated macrophages. Evidence were brought that the anti-inflammatory activity may result from inhibition of the NF-κB signaling pathway. This study is the first to provide evidence that cardamom fruit and seed extracts through their antibacterial and anti-inflammatory properties may be therapeutic agents of interest against periodontal infections.

Regulatory Mechanisms of the LuxS/AI-2 System and Bacterial Resistance.

The quorum-sensing (QS) system is an intercellular cell-cell communication mechanism that controls the expression of genes involved in a variety of cellular processes and that plays critical roles in the adaption and survival of bacteria in their environment. The LuxS/AI-2 QS system, which uses AI-2 (autoinducer-2) as a signal molecule, has been identified in both Gram-negative and Gram-positive bacteria. As one of the important global regulatory networks in bacteria, it responds to fluctuations in the numbers of bacteria and regulates the expression of a number of genes, thus affecting cell behavior. We summarize here the known relationships between the LuxS/AI-2 system and drug resistance, discuss the inhibition of LuxS/AI-2 system as an approach to prevent bacterial resistance, and present new strategies for the treatment of drug-resistant pathogens.

Tea polyphenols protect gingival keratinocytes against TNF-α-induced tight junction barrier dysfunction and attenuate the inflammatory response of monocytes/macrophages.

Tea, an aromatic beverage prepared with the leaves of the Camellia sinensis plant, is well known to contain bioactive polyphenols. Green tea contains mainly catechins such as epigallocatechin-3-gallate (EGCG), while black tea is characterized by the presence of theaflavins. TNF-α, which is a pro-inflammatory cytokine that activates the endogenous inflammatory cascade, plays a key role in periodontitis. In the present study, we investigated the ability of tea compounds to attenuate TNF-α-mediated activation of the host inflammatory response in monocytes/macrophages as well as the protective effect of green and black tea polyphenols on gingival keratinocyte barrier dysfunction induced by TNF-α. Tea compounds inhibited both the activation of NF-κB and caspase-1 as well as IL-1ß secretion by monocytes/macrophages. TNF-α time-dependently damaged keratinocyte tight junction barrier integrity, as determined by changes in transepithelial electrical resistance and FITC-dextran transport. Green tea extract, EGCG, theaflavins, and to a lesser extent, black tea extract protected keratinocytes against the TNF-α-mediated breakdown of barrier integrity. The treatment of keratinocytes with tea polyphenols markedly mitigated the morphological changes of tight junction proteins such as zonula occludens-1 and occludin compared to cells exposed only to TNF-α, as determined by immunofluorescence. Tea polyphenols also time-dependently decreased the paracellular flux of TNF-α-treated keratinocytes. In conclusion, the ability of tea polyphenols to exert an anti-inflammatory effect and to attenuate the gingival epithelial barrier dysfunction induced by TNF-α supports their potential for the prevention and treatment of periodontal disease.

Antibacterial activity against porcine respiratory bacterial pathogens and in vitro biocompatibility of essential oils.

Bacterial respiratory infections affecting pigs such as pneumonia, pleuropneumonia, and pleurisy, are a major health concern in the swine industry and are associated with important economic losses. This study aimed to investigate the antibacterial activities of essential oils against major swine respiratory pathogens with a view to developing a potential alternative to antibiotics. Their synergistic interactions with the bacteriocin nisin was also examined. Lastly, we assessed the in vitro biocompatibility of the most efficient essential oils using a pig tracheal epithelial cell line. Of the nine essential oils tested, those from cinnamon, thyme, and winter savory were the most active against Streptococcus suis, Actinobacillus pleuropneumoniae, Actinobacillus suis, Bordetella bronchiseptica, Haemophilus parasuis, and Pasteurella multocida, with minimum inhibitory concentrations and minimum bactericidal concentrations ranging from 0.01 to 0.156% (v/v). The main component found in cinnamon, thyme, and winter savory oils were cinnamaldehyde, thymol, and carvacrol, respectively. Treating pre-formed S. suis and A. pleuropneumoniae biofilms with thyme or winter savory oils significantly decreased biofilm viability. We also observed a synergistic growth inhibition of S. suis with mixtures of nisin and essential oils from thyme and winter savory. Concentrations of nisin and cinnamon, thyme and winter savory essential oils that were effective against bacterial pathogens had no effect on the viability of pig tracheal epithelial cells. The present study brought evidence that essential oils are potential antimicrobial agents against bacteria associated with porcine respiratory infections.

Anti-biofilm and anti-adherence properties of novel cyclic dipeptides against oral pathogens.

Microorganisms embedded in a biofilm are significantly more resistant to antimicrobial agents and the defences of the human immune system, than their planktonic counterpart. Consequently, compounds that can inhibit biofilm formation are of great interest for novel therapeutics. In this study, a screening approach was used to identify novel cyclic dipeptides that have anti-biofilm activity against oral pathogens. Five new active compounds were identified that prevent biofilm formation by the cariogenic bacterium Streptococcus mutans and the pathogenic fungus Candida albicans. These compounds also inhibit the adherence of microorganisms to a hydroxylapatite surface. Further investigations were conducted on these compounds to establish the structure-activity relationship, and it was deduced that the common cleft pattern is required for these molecules to act effectively against biofilms.

Enolase and dipeptidyl peptidase IV protein sub-unit vaccines are not protective against a lethal Streptococcus suis serotype 2 challenge in a mouse model of infection.

BACKGROUND: Streptococcus suis is a major swine pathogen causing arthritis, meningitis and sudden death in post-weaning piglets and is also a zoonotic agent. S. suis comprises 35 different serotypes of which the serotype 2 is the most prevalent in both pigs and humans. In the absence of commercial vaccines, bacterins (mostly autogenous), are used in the field, with controversial results. In the past years, the focus has turned towards the development of sub-unit vaccine candidates. However, published results are sometimes contradictory regarding the protective effect of a same candidate. Moreover, the adjuvant used may significantly influence the protective capacity of a given antigen. This study focused on two protective candidates, the dipeptidyl peptidase IV (DPPIV) and the enolase (SsEno). Both proteins are involved in S. suis pathogenesis, and while contradictory protection results have been obtained with SsEno in the past, no data on the protective capacity of DPPIV was available. RESULTS: Results showed that among all the field strains tested, 86 and 88% were positive for the expression of the SsEno and DPPIV proteins, respectively, suggesting that they are widely expressed by strains of different serotypes. However, no protection was obtained after two vaccine doses in a CD-1 mouse model of infection, regardless of the use of four different adjuvants. Even though no protection was obtained, significant amounts of antibodies were produced against both antigens, and this regardless of the adjuvant used. CONCLUSIONS: Taken together, these results demonstrate that S. suis DPPIV and SsEno are probably not good vaccine candidates, at least not in the conditions evaluated in this study. Further studies in the natural host (pig) should still be carried out. Moreover, this work highlights the importance of confirming results obtained by different research groups.

Selective bacterial degradation of the extracellular matrix attaching the gingiva to the tooth.

The junctional epithelium (JE) is a specialized portion of the gingiva that seals off the tooth-supporting tissues from the oral environment. This relationship is achieved via a unique adhesive extracellular matrix that is, in fact, a specialized basal lamina (sBL). Three unique proteins - amelotin (AMTN), odontogenic ameloblast-associated (ODAM), and secretory calcium-binding phosphoprotein proline-glutamine rich 1 (SCPPPQ1) - together with laminin-332 structure the supramolecular organization of this sBL and determine its adhesive capacity. Despite the constant challenge of the JE by the oral microbiome, little is known of the susceptibility of the sBL to bacterial degradation. Assays with trypsin-like proteases, as well as incubation with Porphyromonas gingivalis, Prevotella intermedia, and Treponema denticola, revealed that all constituents, except SCPPPQ1, were rapidly degraded. Porphyromonas gingivalis was also shown to alter the supramolecular network of reconstituted and native sBLs. These results provide evidence that proteolytic enzymes and selected gram-negative periodontopathogenic bacteria can attack this adhesive extracellular matrix, intimating that its degradation could contribute to progression of periodontal diseases.

Determination of the effects of cinnamon bark fractions on Candida albicans and oral epithelial cells.

BACKGROUND: Candida albicans is an opportunistic pathogen that causes oral candidiasis and denture stomatitis. It has also been reported to infect oral mucositis lesions in patients who suffer from cancer affecting the head and neck and who receive chemotherapy and radiotherapy treatments. This study aimed to investigate the effects of two cinnamon bark fractions, i.e., an essential oil and an aqueous extract enriched in proanthocyanidins (Cinnulin PF®) on growth, biofilm formation, and adherence properties of C. albicans as well as on oral epithelial cells (barrier integrity, inflammatory response). METHODS: A microplate dilution assay was used to determine antifungal and anti-biofilm properties. A fluorescent assay was used to determine C. albicans adherence to oral epithelial cells. Cytotoxicity toward oral epithelial cells was assessed by determination of cell metabolic activity. Tight junction integrity of gingival keratinocytes was assessed by determination of transepithelial electrical resistance. IL-6 and IL-8 secretion by TNFα-stimulated oral epithelial cells was quantified by ELISA. RESULTS: While Cinnulin PF® did not reduce C. albicans growth, the cinnamon bark oil exhibited high antifungal activity with minimum inhibitory concentrations and minimum fungicidal concentrations in the range of 0.039 to 0.078%. The cinnamon oil was also active against a pre-formed C. albicans biofilm. Interestingly, Cinnulin PF® prevented biofilm formation by C. albicans and attenuated its adherence to oral epithelial cells. At their effective concentrations, the cinnamon oil and the Cinnulin PF® displayed no significant cytotoxicity against oral epithelial cells. In an in vitro model, both cinnamon fractions reinforced the integrity of the oral epithelial barrier. Lastly, Cinnulin PF® inhibited the secretion of interleukin-6 and interleukin-8 by oral epithelial cells stimulated with TNF-α. CONCLUSION: By their ability to attenuate growth, biofilm formation and adherence property of C. albicans, to reinforce the epithelial barrier function, and to exert anti-inflammatory properties the two cinnamon fractions (essential oil, Cinnulin PF®) investigated in the present study may be promising agents for treating oral infections involving C. albicans.

Treponema denticola chymotrypsin-like proteinase may contribute to orodigestive carcinogenesis through immunomodulation.

BACKGROUND: Periodontal pathogens have been linked to oral and gastrointestinal (orodigestive) carcinogenesis. However, the exact mechanisms remain unknown. Treponema denticola (Td) is associated with severe periodontitis, a chronic inflammatory disease leading to tooth loss. The anaerobic spirochete Td is an invasive bacteria due to its major virulence factor chymotrypsin-like proteinase. Here we aimed to investigate the presence of Td chymotrypsin-like proteinase (Td-CTLP) in major orodigestive tumours and to elucidate potential mechanisms for Td to contribute to carcinogenesis. METHODS: The presence of Td-CTLP within orodigestive tumour tissues was examined using immunohistochemistry. Oral, tonsillar, and oesophageal squamous cell carcinomas, alongside gastric, pancreatic, and colon adenocarcinomas were stained with a Td-CTLP-specific antibody. Gingival tissue from periodontitis patients served as positive controls. SDS-PAGE and immunoblot were used to analyse the immumodulatory activity of Td-CTLP in vitro. RESULTS: Td-CTLP was present in majority of orodigestive tumour samples. Td-CTLP was found to convert pro MMP-8 and -9 into their active forms. In addition, Td-CTLP was able to degrade the proteinase inhibitors TIMP-1, TIMP-2, and α-1-antichymotrypsin, as well as complement C1q. CONCLUSIONS: Because of its presence within tumours and regulatory activity on proteins critical for the regulation of tumour microenvironment and inflammation, the Td-CTLP may contribute to orodigestive carcinogenesis.

Dipeptidylpeptidase IV of Streptococcus suis degrades the porcine antimicrobial peptide PR-39 and neutralizes its biological properties.

Streptococcus suis is a major swine pathogen causing pathologies such as meningitis, sepsis, endocarditis, and arthritis. Several surface-bound and secreted proteases produced by S. suis have been identified and proposed as virulence factors. PR-39 is a proline/arginine-rich antimicrobial peptide produced by porcine leucocytes. In addition to play a role in innate immunity, this peptide possesses immunomodulatory properties. In this study, we hypothesized that proteases produced by S. suis inactivate PR-39. Most strains of S. suis tested were relatively resistant to PR-39, with minimal inhibitory concentration (MIC) values ≥ 200 µg/ml. The proteolytic cleavage of PR-39 by recombinant subtilisin-like protease and dipeptidylpeptidase IV (DPPIV) of S. suis was assessed by SDS-PAGE. While PR-39 was not cleaved by the subtilisin-like protease, it was time-dependently degraded by DPPIV. Whole cells of S. suis also degraded PR-39. When S. suis was grown in a culture medium supplemented with recombinant DPPIV, its susceptibility to PR-39 was decreased. Activation of brain microvascular endothelial cells with PR-39 resulted in an increased secretion of the chemokine interleukin-8 (IL-8) thus confirming the immunomodulatory activity of this porcine antimicrobial peptide. However, a pre-treatment of PR-39 with DPPIV completely neutralized the increased IL-8 secretion. In this study, we showed that DPPIV produced by S. suis can degrade PR-39 and neutralize its antibacterial and immunomodulatory properties. This may allow survival of S. suis in the central nervous system by resisting to killing by this antimicrobial peptide and delaying the recruitment of phagocytic cells such as neutrophils to the site of infection.

In vitro antibacterial activity of plant essential oils against Staphylococcus hyicus and Staphylococcus aureus, the causative agents of exudative epidermitis in pigs.

Greasy pig disease or exudative epidermitis, a generalized or localized skin disease affecting piglets, is mainly caused by Staphylococcus hyicus, although other staphylococcal species such as Staphylococcus aureus may also induce disease. Piglets with skin lesions can be treated systemically with antibiotics. However, antimicrobial resistance to ß-lactam antibiotics are now frequently observed in S. hyicus and S. aureus isolates. In this study, the antibacterial activity of plant essential oils as well as their ability to potentiate the effect of several antimicrobial compounds against S. hyicus and S. aureus were investigated with a view to a potential use as skin disinfectants. Among ten essential oils tested, those from cinnamon, thyme, and winter savory were the most active with minimal inhibitory concentration (MIC) and minimal bactericidal concentration (MBC) values ranging from 0.078 to 0.313% (v/v). Using a fluorescent probe with DNA affinity, it was found that thyme and winter savory oils act, at least in part, by disturbing the bacterial membrane integrity. At concentrations below the MIC, thyme and winter savory oils reduced biofilm formation by S. hyicus. Moreover, a treatment of pre-formed biofilms of S. hyicus with cinnamon or thyme oils significantly decreases its viability. Synergistic interactions between essential oils, more particularly from thyme and winter savory, and penicillin G, chlorhexidine or nisin, were observed. This study supports the therapeutic potential of essential oils as topical therapeutic agents against exudative epidermitis.

Characterization of the zinc metalloprotease of Streptococcus suis serotype 2.

Streptococcus suis is a swine pathogen and zoonotic agent responsible for meningitis and septic shock. Although several putative virulence factors have been described, the initial steps of the S. suis pathogenesis remain poorly understood. While controversial results have been reported for a S. suis serotype 2 zinc metalloprotease (Zmp) regarding its IgA protease activity, recent phylogenetic analyses suggested that this protein is homologous to the ZmpC of Streptococcus pneumoniae, which is not an IgA protease. Based on the previously described functions of metalloproteases (including IgA protease and ZmpC), different experiments were carried out to study the activities of that of S. suis serotype 2. First, results showed that S. suis, as well as the recombinant Zmp, were unable to cleave human IgA1, confirming lack of IgA protease activity. Similarly, S. suis was unable to cleave P-selectin glycoprotein ligand-1 and to activate matrix metalloprotease 9, at least under the conditions tested. However, S. suis was able to partially cleave mucin 16 and syndecan-1 ectodomains. Experiments carried out with an isogenic Δzmp mutant showed that the Zmp protein was partially involved in such activities. The absence of a functional Zmp protein did not affect the ability of S. suis to adhere to porcine bronchial epithelial cells in vitro, or to colonize the upper respiratory tract of pigs in vivo. Taken together, our results show that S. suis serotype 2 Zmp is not a critical virulence factor and highlight the importance of independently confirming results on S. suis virulence by different teams.