The otc gene of Streptococcus suis plays an important role in biofilm formation, adhesion, and virulence in a murine model

Pyruvate formate lyase regulates fermentation metabolism and virulence of Streptococcus suis

Streptococcus suis, a zoonotic pathogen, is commonly found as a commensal bacterium in the respiratory tracts of pigs. Under specific conditions, it becomes invasive and enters the blood, causing severe systemic infections. For S. suis, effective acquisition of carbon sources in different host niches is necessary for its survival. However, as of now, our understanding of the metabolism of S. suis within the host is highly restricted. Pyruvate formate lyase (PFL) plays a crucial role in bacterial survival of in glucose-limited and hypoxic host tissues. Here, we investigated the physiological and metabolic functions of PFL PflB in S. suis and elucidated its pivotal role in regulating virulence within the mucosal and blood niches. We demonstrate that PflB is a key enzyme for S. suis to support mixed-acid fermentation under glucose-limited and hypoxic conditions. Additionally, PflB is involved in regulating S. suis morphology and stress tolerance, and its regulation of capsular polysaccharide content depends on dynamic carbon availability. We also found that PflB is associated with the capacity of S. suis to cause bacteremia and persist in the upper respiratory tract to induce persistent infection. Our results provide highly persuasive evidence for the relationship between metabolic regulation and the virulence of S. suis.

Streptococcus suis regulates central carbon fluxes in response to environment to balance drug resistance and virulence

Streptococcus suis, a zoonotic pathogen, must adapt to the distinct nutritional environment of the host microhabitat during infection and the establishment of invasive disease, primarily by modulating its metabolic pathways. Metabolic plasticity endows S. suis with an enhanced capacity for environmental adaptation. Multidrug-resistant S. suis is increasingly prevalent due to the extensive use of antibiotics in swine production. In this study, an environment-dependent evolutionary model demonstrated that S. suis could modulate its metabolism in response to environmental changes, thereby altering its drug resistance and virulence. The central carbon flux regulated by pyruvate dehydrogenase (PDH) was identified as a pivotal node in balancing drug resistance and virulence in S. suis. Within the in vivo host environment, increased carbon flux through PDH enhances the production of capsular polysaccharide (CPS), thereby improving immune evasion. Conversely, in the antibiotic environment, reduced carbon flux through PDH downregulates the bacterial metabolic state, which diminishes the induction of toxic metabolites by antibiotics, thereby augmenting drug resistance. This concept provides a reasonable explanation for the puzzling phenomena observed with S. suis in clinical settings. For instance, antibiotic-resistant S. suis has a survival advantage in pig farms where antibiotics are frequently used but is less frequently associated with invasive infections. Furthermore, this study demonstrates that exogenous pyruvate can enhance the bactericidal effect of gentamicin against clinically multidrug-resistant S. suis, offering new insights and potential strategies for controlling clinical multidrug-resistant S. suis infections.

Andrographolide reverses the susceptibility of Streptococcus suis to aminoglycoside antibiotics by proton motive force

BACKGROUND

The global rise in multidrug-resistant bacteria has significantly undermined the efficacy of traditional antibiotics. Multidrug-resistant Streptococcus suis (S. suis), a pathogen capable of infecting pigs and humans, has been identified as a critical threat, causing severe meningitis and rapid mortality. In response, researchers have increasingly focused on herbal compounds as non-traditional antimicrobial agents, which can inhibit bacterial growth while minimizing the risk of resistance development. This study investigates the mechanism through which andrographolide (AP) restores the susceptibility of S. suis to aminoglycoside antibiotics.

METHODS

The intracellular ΔpH in S. suis was assessed using the 2',7' -bis-(2-carboxyethyl)-5-(and-6)-carboxyfluorescein (BCCF-AM) probe to evaluate alterations in the proton motive force (PMF) following treatment with AP. Non-targeted metabolomics was employed to confirm changes in the metabolic profile of S. suis upon exposure to AP. Finally, an in vivo infection model was utilized to evaluate the therapeutic efficacy of AP in combination with antibiotics.

RESULTS

Extensive in vitro experiments demonstrated that AP significantly enhances the activity of aminoglycoside antibiotics against diverse pathogens, including S. suis. Further studies revealed that bacterial death results from AP-mediated upregulation of the S. suis PMF, which enhances cellular uptake of tobramycin (TOB). Moreover, AP significantly upregulated pyruvate metabolism in S. suis, accelerated the tricarboxylic acid (TCA) cycle, and increased nicotinamide adenine dinucleotide (NADH) production. This metabolic shift further augmented the PMF. Combining AP with aminoglycoside antibiotics significantly reduced bacterial load and organ lesions in various organs in mice.

CONCLUSION

AP holds promise as an adjuvant to aminoglycoside antibiotics for combating S. suis-induced infections, offering a theoretical foundation for clinical applications.

Targeting AI-2 quorum sensing: harnessing natural products against Streptococcus suis biofilm infection

The biofilm acts as a protective layer for Streptococcus suis (S. suis), contributing to the development of drug resistance and chronic infections. Autoinducer 2 (AI-2) quorum sensing represents the primary regulatory pathway governing biofilm formation in S. suis. Consequently, targeting AI-2 quorum sensing to inhibit biofilm formation represents a promising strategy for preventing and managing drug resistance and chronic infections caused by S. suis. This study established a small natural product library by integrating commercial drug molecules with Chinese herbal medicine molecules. Consequently, two natural products, salvianolic acid A (SAA) and rhapontin (RH), which target S. suis AI-2 via quorum sensing, were identified. SAA and RH inhibit AI-2 synthesis through noncompetitive and competitive binding to S-ribosylhomocysteinase (LuxS). By inhibiting S. suis AI-2 quorum sensing, these compounds modulate the expression of adhesion genes and the synthesis of extracellular polysaccharides (EPS), reducing the adhesion ability of S. suis and ultimately inhibiting biofilm formation. Using LC‒MS/MS, we further analysed the impact of SAA and RH on the metabolic activity of S. suis, revealing the potential medicinal value of these compounds. Finally, the efficacy of SAA and RH against S. suis infection was validated in Galleria mellonella larvae, confirming their significant anti-infection effects.

Functional analysis of the type II toxin-antitoxin system ParDE in Streptococcus suis serotype 2

Streptococcus suis (S. suis) is a major pathogen in swine and poses a potential zoonotic threat, which may cause serious diseases. Many toxin-antitoxin (TA) systems have been discovered in S. suis, but their functions have not yet been fully elucidated. In this study, an auto-regulating type II TA system, ParDE, was identified in S. suis serotype 2 strain ZY05719. We constructed a mutant strain, ΔparDE, to explore its functions in bacterial virulence, various stress responses, and biofilm formation capabilities. The toxicity exerted by the toxin ParE can be neutralized by the antitoxin ParD. The β-galactosidase activity analysis indicated that ParDE has an autoregulatory function. An electrophoretic mobility shift assay (EMSA) confirmed that the antitoxin ParD bound to the promoter of ParDE as dimers. In the mouse infection model, the deletion of ParDE in ZY05719 significantly attenuated virulence. ΔparDE also exhibited a reduced anti-oxidative stress ability, and ΔparDE was more susceptible to phagocytosis and killing by macrophages. Moreover, the biofilm formation ability of the ΔparDE strain was significantly enhanced compared to ZY05719. Taken together, these findings indicate that the type II TA system ParDE plays a significant role in the pathogenesis of S. suis, providing new insights into its pathogenic mechanisms.

Identification of immunogenic antigens and evaluation of vaccine candidates against Clostridium perfringens

Necrotic enteritis (NE) caused by Clostridium perfringens (C. perfringens) has resulted in significant losses for the poultry industry worldwide. Currently, there is no widely promoted vaccine for NE. In this study, immunoprecipitation (IP) was employed to isolate immunogenic proteins of C. perfringens, and 118 potential candidate antigens were identified through liquid chromatography-mass spectrometry/mass spectrometry (LC-MS/MS). From these, three candidate antigen proteins were selected based on their predicted antigenicity, hydrophilicity, stability, and transmembrane signalling properties: ArcB (an ornithine aminotransferase), TmpC (a probable membrane lipoprotein), and EntB (a possible enterotoxin). These three proteins were successfully produced in large quantities using Escherichia coli (E. coli), with confirmed good solubility. Both in vitro and in vivo research demonstrated that these antigens possess strong immunogenicity, eliciting robust antigen-specific humoral and cellular immune responses in chickens and mitigating NE symptoms caused by C. perfringens. The candidate antigens identified through immunoproteomics hold potential as subunit vaccines against C. perfringens infection.

Study on the Effect of Phillyrin on Streptococcus suis In Vivo and In Vitro

As a zoonotic pathogen, S. suis serotype 2 (SS2) can cause severe diseases in both pigs and humans, and develop resistance to antibiotics. Plant natural compounds are regarded as promising alternatives to conventional antibiotics. Phillyrin is the major bioactive components of Chinese herbal medicine Forsythia suspensa. In this study, we explored the activity and action mechanism of phillyrin against SS2. The results showed that phillyrin could disrupt membrane integrity, destroy intracellular structures, and increase the exosmosis of DNA. Results of PCR revealed that phillyrin affected bacterial-virulence-related genes' expression levels. Meanwhile, phillyrin significantly decreased the adhesion activity, inhibited lactate dehydrogenase (LDH) secretion, and reduced biofilm formation of SS2 in Newborn pig trachea epithelial (NPTr) cells. Furthermore, phillyrin protected tight junction protein of NPTr cells from SS2. We reported that phillyrin (0.1 mg/kg) treatment after bacterial challenge significantly improved the survival rate, ameliorated pulmonary inflammation, and inhibited the accumulation of multiple cytokines (IL-1, IL-6, IL-8, and TNF-α). Molecular docking showed that phillyrin had a good binding activity with the Ala88 and Asp111 of suilysin (SLY), one of the most important virulence factors of SS2. Collectively, phillyrin possesses antibacterial and anti-inflammatory activities, and is a promising candidate for preventing SS2 infection.

Effects of AI-2 quorum sensing related luxS gene on Streptococcus suis formatting monosaccharide metabolism-dependent biofilm

Biofilm is the primary cause of persistent infections caused by Streptococcus suis (S. suis). Metabolism and AI-2 quorum sensing are intricately linked to S. suis biofilm formation. Although the role of the AI-2 quorum sensing luxS gene in S. suis biofilm has been reported, its specific regulatory mechanism remains unclear. This study explored the differences in biofilm formation and monosaccharide metabolism among the wild type (WT), luxS mutant (ΔluxS) and complement strain (CΔluxS), and Galleria mellonella larvae were used to access the effect of luxS gene deletion on the virulence of S. suis in different monosaccharide medias. The results indicated that deletion of the luxS gene further compromised the monosaccharide metabolism of S. suis, impacting its growth in media with fructose, galactose, rhamnose, and mannose as the sole carbon sources. However, no significant impact was observed in media with glucose and N-acetylglucosamine. This deletion also weakened EPS synthesis, thereby diminishing the biofilm formation capacity of S. suis. Additionally, the downregulation of adhesion gene expression due to luxS gene deletion was found to be independent of the monosaccharide medias of S. suis.

Cooperation of quorum sensing and central carbon metabolism in the pathogenesis of Gram-positive bacteria

Quorum sensing (QS), an integral component of bacterial communication, is essential in coordinating the collective response of diverse bacterial pathogens. Central carbon metabolism (CCM), serving as the primary metabolic hub for substances such as sugars, lipids, and amino acids, plays a crucial role in the life cycle of bacteria. Pathogenic bacteria often utilize CCM to regulate population metabolism and enhance the synthesis of specific cellular structures, thereby facilitating in adaptation to the host microecological environment and expediting infection. Research has demonstrated that QS can both directly or indirectly affect the CCM of numerous pathogenic bacteria, thus altering their virulence and pathogenicity. This article reviews the interplay between QS and CCM in Gram-positive pathogenic bacteria, details the molecular mechanisms by which QS modulates CCM, and lays the groundwork for investigating bacterial pathogenicity and developing innovative infection treatment drugs.

Rethinking the control of Streptococcus suis infection: Biofilm formation

Streptococcus suis is an emerging zoonotic pathogen that is widespread in swine populations. The control of S. suis infection and its associated diseases is a daunting challenge worldwide. Biofilm formation appears to be the main reason for the persistence of S. suis. In this review we gather existing knowledge on S. suis biofilm, describing the role of biofilm formation in S. suis virulence and drug resistance, the regulatory factors of S. suis biofilm formation, and the research progress of inhibiting S. suis biofilm formation, with the aim of providing guidance for future studies related to the field of S. suis biofilms.

Mechanistic insights of magnolol antimicrobial activity against Mycoplasma using untargeted metabolomic analyses

The unreasonable use of antibiotics is one of the important causes of antimicrobial resistance (AMR) that poses a huge public health threat. Magnolol is a traditional Chinese medicine exhibiting antibacterial-, antifungal-, anti-inflammatory-, and antioxidant activities. However, it is unclear whether magnolol has an inhibitory effect on mycoplasma. This study found that magnolol showed excellent inhibitory activity against various mycoplasmas. Magnolol showed dose-dependent inhibition of Mycoplasma synoviae growth and biofilm formation in vitro. Magnolol caused severely sunken and wrinkled M. synoviae cell membranes at the minimum inhibitory concentration, and an enlarged cell diameter. The chicken embryo infection model showed that magnolol significantly reduced M. synoviae pathogenicity in vivo. Kyoto Encyclopedia of Genes and Genomes pathway analysis showed that the citrate cycle, glycolysis/gluconeogenesis, and pyruvate metabolism were significantly disturbed at the minimum inhibitory concentration of magnolol. Interestingly, 41% of differential metabolites were in the categories of lipids and lipid-like molecules. Protegenin A was up-regulated 58752-fold after magnolol treatment. It belongs to fatty acyls, and destroys cell membrane integrity and cell activity. Ghosphatidylethanolamine, phosphatidylglycerol, phosphatidic acid, and phosphatidylserine related to membrane maintenance and stress response were widely down-regulated. Collectively, our results illustrate the feasibility of magnolol as a phytochemical compound to treat mycoplasma infection.

Methyl anthranilate deteriorates biofilm structure of Streptococcus suis and antagonizes the capsular polysaccharide defence effect

BACKGROUND

Streptococcus suis is an important zoonotic pathogen that often causes biofilm-associated infection. Bacterial biofilm-dependent infection is associated with enhanced drug resistance, making it difficult to eradicate. Novel therapeutic approaches are required urgently to treat infections associated with S. suis biofilm. This study aimed to investigate the effects and mechanisms of methyl anthranilate (MA) on S. suis biofilm.

METHODS

The effect of MA on S. suis biofilm was determined using the crystal violet method, and the microstructure of the biofilm was observed by electron microscopy. The effects on capsular polysaccharides were determined using the phenol-sulphuric acid method and high-performance liquid chromatography. Adhesion and antiphagocytosis properties of S. suis were detected via cell assays. Molecular docking, molecular dynamics simulation and enzyme activity inhibition assays were used to further explore the effect of MA on AI-2 quorum sensing (QS) of S. suis. Finally, the therapeutic effect of MA was investigated using a mouse infection model.

RESULTS

MA destroyed the structure of S. suis biofilm, hindered biofilm formation, and reduced the synthesis of capsular polysaccharides significantly, which further weakened the adhesion and antiphagocytosis ability of S. suis. MA had a docking effect and binding site (SER76 and ASP197) similar to S-adenosylhomocysteine (SAH). Further analysis showed that MA competitively bound 5'-methyladenosine/S-adenosine homocysteine nucleosidase with SAH to interfere with AI-2 QS. In a mouse model, MA reduced the bacterial burden and inflammatory infiltrates effectively.

CONCLUSION

This study revealed the antibiofilm effects of MA, and highlighted its potential as a QS inhibitor against S. suis infection.

Evaluating the Antibacterial and Antivirulence Activities of Floxuridine against Streptococcus suis

Streptococcus suis is an emerging zoonotic pathogen that can cause fatal diseases such as meningitis and sepsis in pigs and human beings. The overuse of antibiotics is leading to an increased level of resistance in S. suis, and novel antimicrobial agents or anti-virulence agents for the treatment of infections caused by S. suis are urgently needed. In the present study, we investigated the antibacterial activity, mode of action and anti-virulence effects of floxuridine against S. suis. Floxuridine showed excessive antibacterial activity against S. suis both in vivo and in vitro; 4 × MIC of floxuridine could kill S. suis within 8 h in a time-kill assay. Meanwhile, floxuridine disrupted the membrane structure and permeability of the cytoplasmic membrane. Molecular docking revealed that floxuridine and SLY can be directly bind to each other. Moreover, floxuridine effectively inhibited the hemolytic capacity and expression levels of the virulence-related genes of S. suis. Collectively, these results indicate that the FDA-approved anticancer drug floxuridine is a promising agent and a potential virulence inhibitor against S. suis.

The adcA and lmb Genes Play an Important Role in Drug Resistance and Full Virulence of Streptococcus suis

Streptococcus suis is an recognized zoonotic pathogen of swine and severely threatens human health. Zinc is the second most abundant transition metal in biological systems. Here, we investigated the contribution of zinc to the drug resistance and pathogenesis of S. suis. We knocked out the genes of AdcACB and Lmb, two Zn-binding lipoproteins. Compared to the wild-type strain, we found that the survival rate of this double-mutant strain (ΔadcAΔlmb) was reduced in Zinc-limited medium, but not in Zinc-supplemented medium. Additionally, phenotypic experiments showed that the ΔadcAΔlmb strain displayed impaired adhesion to and invasion of cells, biofilm formation, and tolerance of cell envelope-targeting antibiotics. In a murine infection model, deletion of the adcA and lmb genes in S. suis resulted in a significant decrease in strain virulence, including survival rate, tissue bacterial load, inflammatory cytokine levels, and histopathological damage. These findings show that AdcA and Lmb are important for biofilm formation, drug resistance, and virulence in S. suis. IMPORTANCE Transition metals are important micronutrients for bacterial growth. Zn is necessary for the catalytic activity and structural integrity of various metalloproteins involved in bacterial pathogenic processes. However, how these invaders adapt to host-imposed metal starvation and overcome nutritional immunity remains unknown. Thus, pathogenic bacteria must acquire Zn during infection in order to successfully survive and multiply. The host uses nutritional immunity to limit the uptake of Zn by the invading bacteria. The bacterium uses a set of high-affinity Zn uptake systems to overcome this host metal restriction. Here, we identified two Zn uptake transporters in S. suis, AdcA and Lmb, by bioinformatics analysis and found that an adcA and lmb double-mutant strain could not grow in Zn-deficient medium and was more sensitive to cell envelope-targeting antibiotics. It is worth noting that the Zn uptake system is essential for biofilm formation, drug resistance, and virulence in S. suis. The Zn uptake system is expected to be a target for the development of novel antimicrobial therapies.

Theaflavin Ameliorates Streptococcus suis-Induced Infection In Vitro and In Vivo

Streptococcus suis (S. suis) is one of the most important zoonotic pathogens that threaten the lives of pigs and humans. Even worse, the increasingly severe antimicrobial resistance in S. suis is becoming a global issue. Therefore, there is an urgent need to discover novel antibacterial alternatives for the treatment of S. suis infection. In this study, we investigated theaflavin (TF1), a benzoaphenone compound extracted from black tea, as a potential phytochemical compound against S. suis. TF1 at MIC showed significant inhibitory effects on S. suis growth, hemolytic activity, and biofilm formation, and caused damage to S. suis cells in vitro. TF1 had no cytotoxicity and decreased adherent activity of S. suis to the epithelial cell Nptr. Furthermore, TF1 not only improved the survival rate of S. suis-infected mice but also reduced the bacterial load and the production of IL-6 and TNF-α. A hemolysis test revealed the direct interaction between TF1 and Sly, while molecular docking showed TF1 had a good binding activity with the Glu198, Lys190, Asp111, and Ser374 of Sly. Moreover, virulence-related genes were downregulated in the TF1-treated group. Collectively, our findings suggested that TF1 can be used as a potential inhibitor for treating S. suis infection in view of its antibacterial and antihemolytic activity.

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.

Detection of Streptococcus suis using the optimized real-time polymerase chain reaction protocol

The article presents the results of studies on the detection of Streptococcus suis by real-time polymerase chain reaction. Isolation and species identification of the studied isolates of streptococci was carried out according to morphological, cultural, biochemical and biological properties by conventional methods. The study of cultural characteristics of growth was carried out using conventional bacteriological methods on the brain heart infusion broth (BHI) and BHI agar with the addition of 5% sheep blood (blood BHI agar). To confirm biochemical properties as a confirmatory method, API 20 STREP test kit (bioMerieux, France) was used. In addition, to differentiate S. suis from the non-pathogenic species of streptococci, the hemolysis test was used. As a result of the studies, it was found that the use of the real-time PCR (polymerase chain reaction) method makes it possible to detect S. suis in an amount of 1 x 104 genome copies in the sample. All described validation parameters for the qualitative detection of S. suis DNA by real-time PCR meet international requirements, which guarantees accurate and reliable results. In Ukraine only a diagnostic test kit for convential PCR has been developed for the detection of swine streptococcosis. This approach is more time consuming and complex in comparison with the real-time PCR approach. We recommend that diagnostic laboratories implement this method in their practice. This will increase the number of effective diagnostic tools available to veterinarians on pig farms when they order laboratory tests. The high analytical sensitivity limit of a test is an essential parameter when screening is the focus, and obtaining false negative results causes a risk of the development of infection process among pig populations within infected herds. Our study showed that microbiological diagnostic methods to determine morphological and cultural properties can identify S. suis at the genus level. Determination of biochemical properties using the API 20 STREP test kit can be used to identify S. suis 1 and 2 serotypes. The conventional method and real-time PCR have 100% specificity and can be used to identify S. suis of different serotypes. Real-time PCR is a 2 to 4 times more sensitive limit than conventional PCR depending on the serotype being studied, and can be used to more accurately identify streptococcal DNA. It was found that the use of the real-time PCR method makes it possible to detect S. suis in an amount of 1 x 104 copies of the genome in the sample. Additionally, it was found that all the studied validation parameters of the qualitative method for determining S. suis DNA by real-time PCR meet international requirements, which guarantees accurate and reliable results.

Paeoniflorin reduce luxS/AI-2 system-controlled biofilm formation and virulence in Streptococcus suis

Streptococcus suis (S. suis), more specifically serotype 2, is a bacterial pathogen that threatens the lives of pigs and humans. Like many other pathogens, S. suis exhibits quorum sensing (QS) system-controlled virulence factors, such as biofilm formation that complicates treatment. Therefore, impairing the QS involving LuxS/AI-2 cycle in S. suis, may be a promising alternative strategy for overcoming S. suis infections. In this study, we investigated paeoniflorin (PF), a monoterpenoid glycoside compound extracted from peony, as an inhibitor of S. suis LuxS/AI-2 system. At a sub-minimal inhibitory concentration (MIC) (1/16 MIC; 25 μg/ml), PF significantly reduced biofilm formation by S. suis through inhibition of extracellular polysaccharide (EPS) production, without affecting bacterial growth. Moreover, evidence was brought that PF reduces AI-2 activity in S. suis biofilm. Molecular docking indicated that LuxS may be the target of PF. Monitoring LuxS enzymatic activity confirmed that PF had a partial inhibitory effect. Finally, we showed that the use of PF in a mouse model can relieve S. suis infections. This study highlighted the anti-biofilm potential of PF against S. suis, and brought evidence that it may as an inhibitor of the LuxS/AI-2 system to prevent S. suis biofilm-related infections. PF can thus be used as a new type of natural biofilm inhibitor for clinical application.

mRNA-Seq reveals the quorum sensing system luxS gene contributes to the environmental fitness of Streptococcus suis type 2

Background

Streptococcus suis type 2 (SS2) is an important zoonotic pathogen. We have previously reported the structure of LuxS protein and found that the luxS gene is closely related to biofilm, virulence gene expression and drug resistance of SS2. However, the mechanism of luxS mediated SS2 stress response is unclear. Therefore, this experiment performed stress response to luxS mutant (ΔluxS) and complement strain (CΔluxS), overexpression strain (luxS+) and wild-type SS2 strain HA9801, and analyzed the differential phenotypes in combination with transcriptome data.

Results

The results indicate that the luxS gene deletion causes a wide range of phenotypic changes, including chain length. RNA sequencing identified 278 lx-regulated genes, of which 179 were up-regulated and 99 were down-regulated. Differential genes focus on bacterial growth, stress response, metabolic mechanisms and drug tolerance. Multiple mitotic genes were down-regulated; while the ABC transporter system genes, cobalamin /Fe³⁺-iron carrier ABC transporter ATPase and oxidative stress regulators were up-regulated. The inactivation of the luxS gene caused a significant reduction in the growth and survival in the acid (pH = 3.0, 4.0, 5.0) and iron (100 mM iron chelator 2,2′-dipyridyl) stress environments. However, the mutant strain ΔluxS showed increased antioxidant activity to H₂O₂ (58.8 mmol/L).

Conclusions

The luxS gene in SS2 appears to play roles in iron metabolism and protective responses to acidic and oxidative environmental conditions.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12866-021-02170-w.

LytR plays a role in normal septum formation and contributes to full virulence in Streptococcus suis

Streptococcus suis (S. suis) is a major zoonotic pathogen and is also responsible for variety of diseases in swine. LytR-CpsA-Psr (LCP) family proteins affect the biofilm formation and virulence of some Gram-positive bacteria, but we know nothing about their roles in S. suis. In this study, we constructed the LytR mutant and its revertant strains by natural transformation and verified them by PCR and western blot. We explored the effects of LytR on the cell morphology of S. suis. Transmission electron microscopic analysis showed that the mutant strain displayed aberrant septum placement with no obvious differences in capsular thickness. Crystal violet staining and laser-scanning confocal microscopy both revealed that LytR contributes to the biofilm formation of S. suis. The LytR mutant strain had reduced survival in whole human blood and was more sensitive to killing by polymorphonuclear leukocytes (PMNs). Furthermore, in a mouse infection model, the LytR mutant strain also exhibited significantly attenuated virulence and was more easily cleared in the blood. These results indicate that the LytR protein is involved in septum placement, biofilm formation and required for full virulence of S. suis during infection.