Membrane vesicles derived from Streptococcus suis serotype 2 induce cell pyroptosis in endothelial cells via the NLRP3/Caspase-1/GSDMD pathway

Streptococcus suis serotype 2(S.suis 2)is a zoonotic pathogen that clinically causes severe swine and human infections(such as meningitis,endocarditis,and septicemia).In order to cause widespread diseases in different organs,S.suis 2 must colonize the host,break the blood barrier,and cause exaggerated inflammation.In the last few years,most studies have focused on a single virulence factor and its influences on the host.Membrane vesicles(MVs)can be actively secreted into the extracellular environment contributing to bacteria-host interactions.Gram-negative bacteria-derived outer membrane vesicles(OMVs)were recently shown to activate host Caspase-11-mediated non-canonical inflammasome pathway via deliverance of OMV-bound lipopolysaccharide(LPS),causing host cell pyroptosis.However,little is known about the effect of the MVs from S.suis 2(Gram-positive bacteria without LPS)on cell pyroptosis.Thus,we investigated the molecular mechanism by which S.suis 2 MVs participate in endothelial cell pyroptosis.In this study,we used proteomics,electron scanning microscopy,fluorescence microscope,Western blotting,and bioassays,to investigate the MVs secreted by S.suis 2.First,we demonstrated that S.suis 2 secreted MVs with an average diameter of 72.04 nm,and 200 proteins in MVs were identified.Then,we showed that MVs were transported to cells via mainly dynamin-dependent endocytosis.The S.suis 2 MVs activated NLRP3/Caspase-1/GSDMD canonical inflammasome signaling pathway,resulting in cell pyroptosis,but it did not activate the Caspase-4/-5 pathway.More importantly,endothelial cells produce large amounts of reactive oxygen species(ROS)and lost their mitochondrial membrane potential under induction by S.suis 2 MVs.The results in this study suggest for the first time that MVs from S.suis 2 were internalized by endothelial cells via mainly dynamin-dependent endocytosis and might promote NLRP3/Caspase-1/GSDMD pathway by mitochondrial damage,which produced mtDNA and ROS under induction,leading to the pyroptosis of endothelial cells.

Dihydroartemisinin ameliorates innate inflammatory response induced by Streptococcus suis-derived muramidase-released protein via inactivation of TLR4-dependent NF-kB signaling

Muramidase-released protein(MRP)is now being recognized as a critical indicator of the virulence and pathogenicity of Streptococcus suis(S.suis).However,the identification of viable therapeutics for S.suis infection was hindered by the absence of an explicit mechanism for MRP-actuated inflammation.Dihydroartemisinin(DhA)is an artemisinin derivative with potential anti-inflammatory activity.The modulatory effect of DhA on the inflammatory response mediated by the virulence factor MRP remains obscure.This research aimed to identify the signaling mechanism by which MRP triggers the innate immune response in mouse spleen and cultured macrophages.With the candidate mechanism in mind,we investigated DhA for its ability to dampen the pro-inflammatory response induced by MRP.The innate immune response in mice was drastically triggered by MRP,manifesting as splenic and systemic inflammation with splenomegaly,immune cell infiltration,and an elevation in pro-inflammatory cytokines.A crucial role for Toll-like receptor 4(TLR4)in coordinating the MRP-mediated inflammatory response via nuclear factor-kappa B(NF-kB)activation was revealed by TLR4 blockade.In addition,NFkB-dependent transducer and activator of transcription 3(STAT3)and mitogen-activated protein kinases(MAPKs)activation was required for the inflammatory signal transduction engendered by MRP.Intriguingly,we observed an alleviation effect of DhA on the MRP-induced immune response,which referred to the suppression of TLR4-mediated actuation of NF-kB-STAT3/MAPK cascades.The inflammatory response elicited by MRP is relevant to TLR4-dependent NF-kB activation,followed by an increase in the activity of STAT3 or MAPKs.DhA mitigates the inflammation process induced by MRP via blocking the TLR4 cascade,highlighting the therapeutic potential of DhA in targeting S.suis infection diseases.

Epidemiological observations of invasive group B Streptococcus infections in six major hospitals in Peninsular Malaysia

Objective:To address the lack of research on invasive group B Streptococcus(GBS)infections in Malaysia and Southeast Asia through a comprehensive analysis of GBS isolates obtained from hospitals.Methods:Medical records from patients with GBS infection isolated from the sterile site,such as blood and cerebrospinal fluid from 14 July 2019 to 15 December 2020,were reviewed from six major hospitals in Peninsular Malaysia.Inclusion criteria were invasive GBS,sterile sites and non-repeated GBS isolated from the same patients in the same admission.Viable isolates were re-identified for GBS and serotyped.Results:A total of 118 patients were eligible,with a majority of non-pregnant adults(76.3%).Over half of the patients(62.7%)had underlying medical conditions,with diabetes as the most common disease,followed by respiratory disease,renal disease,cardiovascular disease and skin and soft tissue disease.The most common manifestations were sepsis,followed by soft tissue abscess,diabetic foot ulcer,wet gangrene and cellulitis.The overall mortality was 7.6%.The most common serotype was serotype桋.Conclusions:Invasive GBS infection among non-pregnant adults showed a rising trend,particularly among diabetic individuals.The study underscores the importance of reducing risk factors and highlights the necessity of developing GBS vaccination as a preventive strategy for both infants and adults.

Strain-specific effect of Streptococcus thermophilus consumption on host physiology

Streptococcus thermophilus is one of the most prevalent species in stool samples of westernized populations due to continuous exposure to fermented dairy products.However,few studies have explored the effect on host physiology by multiple S.thermophilus strains and considered the inter-strain differences in regulating host.In the present study,we investigated how four S.thermophilus strains influenced the gut microbiota,mucin changes,and host metabolism after 28 days of intervention in conventional mice.The results indicated that the consumption of S.thermophilus affected the host with strain specificity.Among four S.thermophilus strains,DYNDL13-4 and DQHXNQ38M61,especially DQHXNQ38M61,had more effect on host physiology by modulating gut microbiota and host metabolism than LMD9 and 4M6.Ingestion of strains DYNDL13-4 and DQHXNQ38M61 resulted in more remarkable changes in amino acid metabolism and lipid metabolism than that of strains LMD9 and 4M6,which may be related to the elevation of intestinal Bifidobacterium by DYNDL13-4 and DQHXNQ38M61.The enriched Coriobacteriaceae UCG-002,Rikenellaceae RC9 gut group,and Lactobacillus only in the DQHXNQ38M61 group,had a close relationship with the prominent effect of DQHXNQ38M61 on regulating amino acid and lipid metabolism.In addition,DQHXNQ38M61 had a strong influence on degrading colonic mucin fucose by decreasedα-fucosidase activity in feces,and improving mucin sulfation by upregulated Gal3ST2 expression.Comparative genomic analysis revealed that the four S.thermophilus strains belonged to different branches in the phylogenetic tree,and DYNDL13-4 and DQHXNQ38M61 had more genes involved in carbohydrate metabolism,amino acid metabolism,membrane transport,and signal transduction,which may confer the capacity of nutrient utilization and gastrointestinal adaptation of the strains and be associated with their strong regulation in host.Our study provides valuable information for understanding the regulation of host metabolism after consuming different S.thermophilus strains and could facilitate potential personalized applications of S.thermophilus based on strain varieties.

Antibiotic Resistance Profile of Serotypes of Streptococcus pneumoniae Strains in Bangui, from 2017 to 2022: Case of Serotype 1

Goals: The aim of this study was to determine the antibiotic resistance profile of serotypes of Streptococcus pneumoniae strains circulating in Bangui. Methodology: A prospective and analytical analysis was carried out at the National Laboratory of Clinical Biology and Public Health from 2017 to 2022. The strains came from our study on the contribution to the study of antibiotic sensitivity of Streptococcus pneumoniae strains. The multiplex PCR test was used for its cost-effectiveness in terms of amplifiers which can be purified in order to be sequenced. It also makes it possible to detect several germs as well as their serotypes. For a PCR reaction, several elements are involved in the reaction medium or Master Mix. These are the desoxyribonucleotides (dNTPs), the magnesium ions (MgCl2) and the primers. A set of 14 primers divided into 3 classes were used. Class 1 primers served as an internal control by targeting the cpsA gene. It is a highly conserved gene found in capsular loci characterized to date. The primers of the second class were used to target specific serotypes by specific reactions (out of six possibilities). The group reaction was carried out using the primers of the third class in order to carry out an initial screening of the samples and to classify the pneumococcal isolates. Related serotypes were grouped based on the amplification of common genes. Using the technique of electrophoresis on agarose gel and an ultraviolet radiation device, the migration bands are then visualized and analyzed. The data collected had been entered into Excel 2010 and analyzed with Epi info 7. The exact Fischer chi2 test at the 5% threshold, the relative risk and its 95% confidence interval were used to compare the proportions and determine the associations. Results: 187 antibiotic-resistant strains of Streptococcus pneumoniae were collected. The average frequency of serotypes 1, 9A, 4 and untypeable identified were 43.59%, 18.18%, 18.27% and 39.57% respectively. The frequency of serotype 1 was predominant for the age group over five years old with 56.88%. The male sex was predominant with 55.08% for serotype 1. Resistance to penicillin and gentamicin for serotype 1 during this study, for the age group under 5 years old, was 77%. For serotypes 19A and 4, tetracycline resistance was predominant with 20% for the age group under 5 years. The resistance to penicillin and gentamicin of non-typeable serotypes was 33% for the age group under 5 years old. For the age group over 5 years old, resistance to erythromycin predominated at 37%. The distribution of serotypes by sex depending on antibiotic resistance was variable. There was a statistically significant association between identified serotypes and antibiotic resistance (p Conclusion: The study determined serotypes 1, serotypes 19A, serotypes 4 and non-typeable serotypes. These results would be due to the quality of vaccination or poor protection of vaccines.

Protective eff ect and mechanism of nanoantimicrobial peptide ND-C14 against Streptococcus pneumoniae infection

BACKGROUND:Streptococcus pneumoniae(S.pneumoniae)is a common pathogen that causes bacterial pneumonia.However,with increasing bacterial resistance,there is an urgent need to develop new drugs to treat S.pneumoniae infections.Nanodefensin with a 14-carbon saturated fatty acid(ND-C14)is a novel nanoantimicrobial peptide designed by modifying myristic acid at the C-terminus of humanα-defensin 5(HD5)via an amide bond.However,it is unclear whether ND-C14 is effective against lung infections caused by S.pneumoniae.METHODS:In vitro,three groups were established,including the control group,and the HD5 and ND-C14 treatment groups.A virtual colony-count assay was used to evaluate the antibacterial activity of HD5 and ND-C14 against S.pneumoniae.The morphological changes of S.pneumoniae treated with HD5 or ND-C14 were observed by scanning electron microscopy.In vivo,mice were divided into sham,vehicle,and ND-C14 treatment groups.Mice in the sham group were treated with 25μL of phosphate-buffered saline(PBS).Mice in the vehicle and ND-C14 treatment groups were treated with intratracheal instillation of 25μL of bacterial suspension with 2×108 CFU/mL(total bacterial count:5×10^(6) CFU),and then the mice were given 25μL PBS or intratracheally injected with 25μL of ND-C14(including 20μg or 50μg),respectively.Survival rates were evaluated in the vehicle and ND-C14 treatment groups.Bacterial burden in the blood and bronchoalveolar lavage fluid were counted.The lung histology of the mice was assessed.A propidium iodide uptake assay was used to clarify the destructive eff ect of ND-C14 against S.pneumoniae.RESULTS:Compared with HD5,ND-C14 had a better bactericidal eff ect against S.pneumoniae because of its stronger ability to destroy the membrane structure of S.pneumoniae in vitro.In vivo,ND-C14 significantly delayed the death time and improved the survival rate of mice infected with S.pneumoniae.ND-C14 reduced bacterial burden and lung tissue injury.Moreover,ND-C14 had a membrane permeation eff ect on S.pneumoniae,and its destructive ability increased with increasing ND-C14 concentration.CONCLUSION:The ND-C14 may improve bactericidal eff ects on S.pneumoniae both in vitro and in vivo.

Streptococcus anginosus in the development and treatment of precancerous lesions of gastric cancer

The microbiota is strongly association with cancer.Studies have shown significant differences in the gastric microbiota between patients with gastric cancer(GC)patients and noncancer patients,suggesting that the microbiota may play a role in the development of GC.Although Helicobacter pylori(H.pylori)infection is widely recognized as a primary risk factor for GC,recent studies based on microbiota sequencing technology have revealed that non-H.pylori microbes also have a significant impact on GC.A recent study discovered that Streptococcus anginosus(S.anginosus)is more prevalent in the gastric mucosa of patients with GC than in that of those without GC.S.anginosus infection can spontaneously induce chronic gastritis,mural cell atrophy,mucoid chemotaxis,and heterotrophic hyperplasia,which promote the development of precancerous lesions of GC(PLGC).S.anginosus also disrupts the gastric barrier function,promotes the proliferation of GC cells,and inhibits apoptosis.However,S.anginosus is underrepresented in the literature.Recent reports suggest that it may cause precancerous lesions,indicating its emerging pathogenicity.Modern novel molecular diagnostic techniques,such as polymerase chain reaction,genetic testing,and Ultrasensitive Chromosomal Aneuploidy Detection,can be used to gastric precancerous lesions via microbial markers.Therefore,we present a concise summary of the relationship between S.anginosus and PLGC.Our aim was to further investigate new methods of preventing and treating PLGC by exploring the pathogenicity of S.anginosus on PLGC.

Acute coalescent mastoiditis in a 16-month-old child due to Streptococcus pneumoniae infection

Rationale:Acute otitis media is a common disease in early childhood,and is usually caused by Streptococcus pneumoniae(S.pneumoniae).Acute mastoiditis is a complication of acute otitis media and can involve not only the mucoperiosteum of the middle ear but can also spread to the periosteum by destroying the mastoid bone(acute coalescent mastoiditis).In addition,the infection can extend through the surrounding bones or the emissary veins beyond the mastoid’s air cells,leading to subperiosteal abscesses.Patient’s Concern:A 16-month-old female patient was hospitalized due to the purulent discharge of the left ear and the symptoms of right mastoiditis(swelling and redness of the skin).Diagnosis:Bilateral acute coalescent mastoiditis caused by S.pneumoniae infection.The computer tomography revealed bilateral bone destruction of the mastoid and abscesses found behind the auricle on both sides.Interventions:The patient underwent intravenous antibiotic therapy and surgical treatment.Outcomes:The patient was discharged 14 days after hospitalization with an improved condition.Lessons:Improperly treated acute coalescent mastoiditis can lead to extracranial and intracranial complications,sometimes serious and even life-threatening.Complications are prevalent in children under 2 years,in whom the disease progresses more rapidly and severely.The vaccination with a 13-valent vaccine may not result in sufficient immunity against S.pneumoniae,a predominant pathogen in children affected by acute coalescent mastoiditis.

Infantile bacterial meningitis combined with sepsis caused by Streptococcus gallolyticus subspecies pasteurianus:A case report

BACKGROUND Streptococcus gallolyticus subspecies pasteurianus(SGSP)is a rare pathogen responsible for infant sepsis and meningitis and is potentially overlooked because it is not included in routine group B streptococcal screenings.Hence,we present a case of SGSP-induced infant meningitis and sepsis,accompanied by bronchopneumonia induced by multidrug-resistant Staphylococcus aureus(MRSA),providing insights into the identification,management,and prognosis of this bacterial infection.CASE SUMMARY A 45-day-old female infant presented with two episodes of high fever(maximum temperature:39.5°C)and two generalized grand mal seizure episodes that lasted over ten seconds and self-resolved without concomitant symptoms.Postadmission,the patient’s C-reactive protein level was 40.73 mg/L,white blood cell count was 13.42×10^(9)/L,neutrophil ratio was 78.4%,procalcitonin level was 7.89μg/L,cerebrospinal fluid(CSF)white cell count was 36×10^(6)/L,multinucleated cell ratio was 95.2%,and protein concentration was 0.41 g/L.Blood and CSF culture revealed that the pathogen was SGSP.The bacterium was sensitive to ampicillin,furazolidone,penicillin,lincomycin,moxifloxacin,rifampicin,vancomycin,and levofloxacin but resistant to clindamycin and tetracycline.Sputum culture revealed the presence of MRSA,which was sensitive to vancomycin.The patient was diagnosed with meningitis and sepsis caused by SGSP,accompanied by bronchopneumonia induced by MRSA.Ceftriaxone(100 mg/kg/d)combined with vancomycin(10 mg/kg/dose,q6h)was given as an anti-infective treatment postadmission.After 12 days of treatment,the infant was discharged from the hospital with normal CSF,blood culture,and routine blood test results,and no complications,such as subdural effusion,were observed on cranial computed tomography.No growth retardation or neurological sequelae occurred during follow-up.CONCLUSION SGPSP-induced infant bacterial meningitis and sepsis should be treated with prompt blood and CSF cultures,and a sensitive antibiotic therapy to ensure a favorable prognosis.

Pulmonary abscess caused by Streptococcus pseudopneumoniae in a child:A case report and review of literature

BACKGROUND Lung abscess found on chest X-ray and computed tomography examinations is rare in infants and young children.Several pathogens can cause lung abscesses,with the most common pathogens being anaerobes,Streptococci and Staphylococcus aureus.Streptococcus pseudopneumoniae(S.pseudopneumoniae)is a member of the Streptococcaceae family,and is mainly isolated from respiratory tract specimens.There are currently no cases of lung abscess caused by S.pseudopneumoniae in the literature.CASE SUMMARY A 2-year-old boy was admitted to hospital due to persistent cough and fever.Lung computed tomography examination suggested the formation of a lung abscess.His diagnosis was not confirmed by testing for serum respiratory pathogens(6 items),respiratory pathogen nucleic acid(27 items),and laboratory culture.Finally,metagenomic next-generation sequencing of bronchoalveolar lavage fluid revealed the presence of S.pseudopneumoniae,confirming its role in causing the lung abscess.After receiving antibiotic treatment,reexamination with lung computed tomography showed that the abscess was resorbed and the patient’s outcome was good.CONCLUSION This is the first report of a lung abscess in a child caused by S.pseudopneumoniae infection.Metagenomic next-generation sequencing of bronchoalveolar lavage fluid is helpful in achieving rapid and accurate pathogen identification.

Brain abscess caused by Streptococcus anginosus group:Three case reports

BACKGROUND This case series investigated the clinical manifestations,diagnoses,and treatment of cerebral abscesses caused by Streptococcus anginosus.We retrospectively analyzed the clinical characteristics and outcomes of three cases of cerebral abscesses caused by Streptococcus anginosus and conducted a comprehensive review of relevant literature.CASE SUMMARY Case 1 presented with a history of left otitis media and exhibited high fever,confusion,and vomiting as primary symptoms.Postoperative pus culture indicated a brain abscess caused by Streptococcus constellatus infection.Case 2 experienced dizziness for two days as the primary symptom.Postoperative pus culture suggested an intermediate streptococcal brain abscess.Case 3:Enhanced head magnetic resonance imaging(MRI)and diffusion-weighted imaging revealed occupancy of the left temporal lobe,initially suspected to be a metastatic tumor.However,a postoperative pus culture confirmed the presence of a brain abscess caused by Streptococcus anginosus infection.The three cases presented in this case series were all patients with community-acquired brain abscesses resulting from angina caused by Streptococcus group infection.All three patients demonstrated sensitivity to penicillin,ceftriaxone,vancomycin,linezolid,chloramphenicol,and levofloxacin.Successful treatment was achieved through stereotaxic puncture,drainage,and ceftriaxone administration with a six-week course of antibiotics.CONCLUSION Preoperative enhanced head MRI plays a critical role in distinguishing brain tumors from abscesses.Selecting the correct early diagnostic methods for brain abscesses and providing timely intervention are very important.This case series was in accordance with the CARE guidelines.

Antimicrobial and synergistic effects of lemongrass and geranium essential oils against Streptococcus mutans,Staphylococcus aureus,and Candida spp.

BACKGROUND The oral cavity harbors more than 700 species of bacteria,which play crucial roles in the development of various oral diseases including caries,endodontic infection,periodontal infection,and diverse oral diseases.AIM To investigate the antimicrobial action of Cymbopogon Schoenanthus and Pelargonium graveolens essential oils against Streptococcus mutans,Staphylococcus aureus,Candida albicans,Ca.dubliniensis,and Ca.krusei.METHODS Minimum microbicidal concentration was determined following Clinical and Laboratory Standards Institute documents.The synergistic antimicrobial activity was evaluated using the Broth microdilution checkerboard method,and the antibiofilm activity was evaluated with the 3-[4,5-dimethylthiazol-2-yl]-2,5 diphenyl tetrazolium bromide assay.Data were analyzed by one-way analysis of variance followed by the Tukey post-hoc test(P≤0.05).RESULTS C.schoenanthus and P.graveolens essential oils were as effective as 0.12%chlorhexidine against S.mutans and St.aureus monotypic biofilms after 24 h.After 24 h P.graveolens essential oil at 0.25%was more effective than the nystatin group,and C.schoenanthus essential oil at 0.25%was as effective as the nystatin group.CONCLUSION C.schoenanthus and P.graveolens essential oils are effective against S.mutans,St.aureus,Ca.albicans,Ca.dubliniensis,and Ca.krusei at different concentrations after 5 min and 24 h.

A Method for Detecting Adhesive Related-Factors of Streptococcus suis Serotype 2 by Real-time PCR

[Objective] This study aimed to establish a method for quantitative detection of mRNA transcriptional level of SS2 adhesive related-factors of Streptococcus suis serotype 2 （SS2） by fluorescent quantitative PCR. []Vlethod] The gene fragments en- coding SS2 adhesive related-factors MRP, FBPS and CPS2J and a housekeeping gene aroA were amplified by reverse transcription PCR from the total RNA of SS2, cloned, and sequenced. The recombinant plasmids containing the target genes were constructed, and used as templates in Real-time PCR. [Result] Dynamic curves, stan- dard curves and melting curves of the adhesive related-factors and aroA were ob- tained by the optimized Real-time PCR system. The standard curves showed a good linear relationship between template copy number and circulation number, and the correlation coefficients （FF） of the standard curves were over 0.995. Also, these as- says were highly specific a^d there was single specific melting peak for every gene. Moreover, the assays were highly sensitive and had a detection limit of 1.0×102 copies in 1 μl of initial templates. Finally, it was highly repeatable and had a coeffi- cient of variation less than 2% for intra-assay. [Conclusion] This study will provide a way to reveal the adhesion mechanism of SS2 to different host cells at molecular level.

Coinfection of Streptococcus suis and Nocardia asiatica in the human central nervous system:A case report

BACKGROUND Streptococcus suis(S.suis)is an anthropozoonotic pathogen that shows clinical manifestations of meningitis,septicemia,and arthritis in infected humans.Nocardia is another type of anthropozoonotic bacteria,with clinical manifestations of skin,lung,and brain abscesses in infected humans.Few intracranial infections caused by S.suis or Nocardia have been reported.To the best of our knowledge,no study has reported a patient with simultaneous intracranial infection by S.suis and Nocardia.CASE SUMMARY A 66-year-old male presented at Liaocheng People’s Hospital(Liaocheng,Shandong Province,China)reporting dizziness with nausea and vomiting.Metagenomic next-generation sequencing(m NGS)was performed on cerebrospinal fluid for examination,and the patient was diagnosed with suppurative meningitis caused by S.suis infection.He received anti-infection treatment with penicillin sodium and ceftriaxone.The patient’s condition initially improved but then deteriorated.Further m NGS of cerebrospinal fluid revealed both S.suis and Nocardia.Imaging examination revealed a brain abscess.Furthermore,a mixed infection of S.suis and Nocardia was detected in the patient’s central nervous system.The patient was treated with antibiotics and sulfamethoxazole.He was discharged after his condition improved.CONCLUSION This case shows that the disease can be recurrent in patients with intracranial infection of a rare pathogen.The possibility of mixed infection should also be considered,especially in patients treated with immunosuppressive agents.m NGS of cerebrospinal fluid is a supplement to conventional microbial pathogen identification methods.Patients with unknown pathogen diagnosis,early extensive use of antibiotics and infection with rare pathogens can be diagnosed by the combination of conventional methods and m NGS of cerebrospinal fluid.

Prevalence of Streptococcus suis Isolated from Clinically Healthy Sows in China

Streptococcus suis is an important pathogen in pigs. Transmission of this pathogen is generally believed to occur between healthy carrier sows and their offspring, so the carrier status of S. suis in healthy sows is important for the control of S. suis infections in pigs, especially in suckling and growing pigs. In this study, the prevalence of S. suis isolated from clinically healthy sows in China was studied for the first time. A total of 1 043 tonsil samples were collected from clinically healthy sows from 10 regions in China from 2005 to 2007. Among the 421 S. suis isolates, 31 strains were identified as capsular type 2. The results showed that S. suis was widespread in swine herds in China with the carrier rates in different herds ranging from 19.5 to 93.9%. Overall, 40.4 and 3.0% of clinically healthy sows harbored S. suis and capsular type 2 in their palatine tonsils, respectively. Statistically significant differences of carrier rates of S. suis and capsular type 2 between the different farms were observed, which was independent of herd sizes and geographic distributions of different herds.

Prokaryotic Expression of Gene Encoding Glutamate Dehydrogenase of Streptococcus suis Serotype 2 and Preparation of Polyclonal Antibodies against Its Expressed Products

[ Objective] To obtain detection antigen for diagnosis of Streptococcus suis infection. [ Method] The complete ORF of glutamate dehy- drogenase （GDH） gene was amplified from the genomic DNA of Streptococcus suis serotype 2 strain SC22 isolated in Sichuan Province by poly- merase chain reaction （PCR）. The resulting product was cloned into the prokaryotic expression vector pET-30a, which was then transformed into E. coil BL21 （DE3）. The identified positive transformants were screened for expression induced by IPTG. The expression products were subjected to SDS-PAGE and the recombinant protein was purified by nickel ion-agarose affinity chromatography. New Zealand rabbits were immunized with the purified recombinant GDH protein to prepare polyclonal antibodies. Titers of the anti-serum were determined by indirect ELISA and Western blot assay. [ Result] The recombinant GDH protein was effectively expressed in the host bacteria, and highly pure recombinant protein was obtained by nickel ion-agarose affinity chromatography. High-titer anti-serum against the recombinant protein was obtained. As evidenced by western blot as- say, the sera could react specifically with the lysates of all detected Streptococcus suis strains. In addition, the recombinant GDH protein could re- act specifically with serum samples collected from five pigs experimentally infected by strain SC22. [ Conclusion] The expressed GDH fusion protein has some common epitopes of natural GDH and can be used as detection antigen to develop ELISA and other diagnostic methods.

A Streptococcus suis serotype 2 caused streptococcal toxic shock syndrome(STSS) in a patient

Streptococcus suis （S. suis） is a Gram-positive, facultatively anaerobic coccus that has been implicated as the cause of a wide range of clinical disease syndromes in swine and other domestic animals. S. suis has also been implicated in disease in humans, especially anaong abattoir workers, swine and pork handlers. Here we report a case of streptococcal toxic shock syndrome（STSS） caused by S. suis in a 59-year-old man. Despite of intensive treatment, the patient died of shock with multiple organ failure 14 h after admission. One bacterial isolate obtained from blood culture was identified to the species level by biochemical tests and serological tests as S. suis serotype 2. Identification was confirmed by PCR amplification of genes encoding 16sRNA of S. suis and the capsule of S. suis serotype 2（cps 23）. Genes encoding virulence factors were also detected. An investigation to identify the source of S. suis revealed that several days before admission the affected man had been handling sick pigs or their meat. Transmission may occur through breaks in the skin of feet with tinea due to that no measures for personal protection was taken. This case should highten awareness of the potential for occupational exposure and human infection with S. suis.

Isolation, Identification and Pathogenicity Analysis of Streptococcus suis Type 2

[Objectives]This study aimed to investigate the pathogenicity,growth characteristics and drug resistance of Streptococcus suis type 2.[Methods]Bacterial isolation and identification,biochemical experiments,determination of growth curve and correlation curve between OD 600 values and viable counts,drug susceptibility tests,pathogenicity analysis,and histopathological observations were carried out.[Results]The Streptococcus strain isolated from infected pigs was identified as Streptococcus suis type 2,which was named TA01 strain.TA01 strain reached the growth peak at 6-8 h post-incubation,and viable counts gradually declined after 8 h of incubation.The correlation equation between OD 600 values and viable counts is y=24.659 x-1.076 1,R^2=0.996 7.TA01 strain was sensitive to penicillin,erythromycin,florfenicol and oxacillin,and resistant to ciprofloxacin,polymyxin B and clindamycin.According to the results of pathogenicity analysis,all the mice in 3.6×10^9 cfu/mouse group died within 48,and these dead mice exhibited acute pyaemia septica.Based on the Reed-Muench formula,it was calculated that LD 50 of TA01 strain was 1.137×10^8 cfu/mouse.Pathological examination showed obvious blue-stained bacteria clusters,accompanied by neutrophil infiltration.[Conclusions]TA01 strain was a virulent strain of Streptococcus suis type 2.Compared with Streptococcus strains which were isolated and reported in China,TA01 strain exhibited strong virulence and rapid proliferation.

Characterization of a Novel Gene, srpA, Conferring Resistance to Streptogramin A, Pleuromutilins, and Lincosamides in Streptococcus suis

Antimicrobial resistance is undoubtedly one of the greatest global health threats. The emergence of multidrug-resistant(MDR) Gram-positive pathogens, such as methicillin-resistant Staphylococcus aureus(MRSA), vancomycin-resistant Enterococcus faecium(VRE), and β-lactamase-resistant Streptococcus pneumonia, has severely limited our antibiotic arsenal. Numerous ribosome-targeting antibiotics, especially pleuromutilins, oxazolidinones, and streptogramins, are viewed as promising alternatives against aggressive MDR pathogens. In this study, we identified a new adenosine triphosphate(ATP)-binding cassete(ABC)-F family determinant, srp A, in Streptococcus suis(S. suis) by means of a comparative analysis of the whole-genome sequences of tiamulin(TIA)-resistant and TIA-sensitive bacteria. Functional cloning confirmed that the deduced gene can mediate cross-resistance to pleuromutilins, lincosamides, and streptogramin A in S. suis and S. aureus. A sequence alignment revealed that Srp A shares the highest amino acid identity with Vga(E)(36%) and shows canonical characteristics of ABC-F family members.In Srp A-ribosome docked compounds, the extended loop region of Srp A approaches the valnemulinbinding pocket in the ribosome peptidyl-transferase center and competes with bound valnemulin. A detailed mutational analysis of the loop residues confirmed that this domain is crucial for Srp A activity,as substitutions or truncations of this region affect the efficiency and specificity of antibiotic resistance.Intracellular antibiotics accumulation indicated that Srp A does not act as an efflux pump, while a ribosome binding assay supported the protective effects of Srp A on the ribosome by preventing antibiotic binding as well as displacing bound drugs. These findings clarify the mechanisms underlying resistance to ribosomal antibiotics.

Advances in pathogenesis of Streptococcus suis serotype 2

Streptococcus suis is one of the major pathogens of swine streptococcosis. Among them, the strongest virulence and highest rate of clinical isolation serotype is S. suis serotype 2（SS2）. Moreover, SS2 is also an important zoonosis pathogen, which caused severe public health issues in China. It has been reported that SS2 has several virulence factors, including muramidase released protein, extracellular factors, capsule, fibronectin-binding protein, enolase, hemolysin, small RNA, biofilm, two-component regulatory systems, STK/STP, etc., whose functions involved in adhesion, anti-phagocytosis, inflammatory pathway activation, invasion, etc. Actually, SS2 has developed a variety of ways to escape from host immune system during evolution. In particularly, capsule could resist phagocytosis through inhibiting sphingosine dependent immune cell recognition, which plays an important role in escaping host inflammation response; moreover, superoxide dismutase encoding by sod A enables SS2 escaping reactive oxygen species（ROS） in host immune cells; besides, binding complement factor h with Fhb could suppress the activation of complement alternative pathway and bactericidal effect. And SS2 could also hinder the formation of neutrophil extracellular traps（NETs） to avoid trapping by swine neutrophils, while host immune globulin could be degraded by Ig A1 hydrolase and Ig M protease. In addition, SS2 could escape host immune defense with the help of multiple transcriptional factors and micro-RNA. So far, the pathogenesis of meningitis, arthritis caused by SS2 infection, is still unclear, and the virulence regulatory mechanism of phosphorylation, micro-RNA need to be further clarified. Importantly, the study of interaction mechanism of pathogen and host contribute to further demonstration the pathogenesis of SS2.