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.

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.

猪链球菌SC124菌株中ICE_Prophage携带耐药基因的水平转移

旨在探究猪链球菌中ICE_Prophage携带耐药基因转移的情况,使用Illumina MiSeq和Pacbio RSII平台对猪链球菌SC124菌株进行了全基因组测序,利用在线网站RAST、ICEberg 3.0、PHASTER和NCBI数据库对SC124菌株的基因组序列进行分析;用肉汤稀释法测定最小抑菌浓度;通过接合试验验证ICE_Prophage携带耐药基因的可转移性;采用反向PCR检测环状中间体的存在;用竞争试验评估接合子是否具有适应性代价。结果显示:猪链球菌SC124菌株中存在携带四环素类、大环内酯类和氨基糖苷类耐药基因的ICE_Prophage(ICE Ssu SC124_ΦSsuSC124);携带四环素类耐药基因的ICE Ssu SC124以5.52×10-9频率发生转移,未发现前噬菌体发生转移;ICE Ssu SC124可以形成一个大小约为3.8 kb的环状中间体;与猪链球菌BAA相比,含有ICE Ssu SC124的接合子在无药物压力选择的作用下不具有竞争优势,接合子会产生一定程度的适应性代价。综上,猪链球菌SC124菌株中存在携带四环素类、大环内酯类和氨基糖苷类耐药基因的ICE_Prophage,ICE Ssu SC124可发生水平转移,其接合子可产生一定程度的适应性代价。

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.

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.

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.

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.

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.

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.

Genomic Characterization of a Streptococcus suis Serotype 2 Isolated from a Human Patient

Streptococcus suis(S. suis) is a Gram-positive zoonotic pathogen. S. suis infection in humans commonly causes meningitis, septicemia, arthritis,and streptococcal toxic shock-like syndrome(STSLS). S. suis has 29 serotypes, of which S. suis serotype 2(SS2) has the highest clinical isolation rate and strongest pathogenicity and causes most S. suis human infections.About 1,000 different sequence types(STs)were identified in S.suis based on multilocus sequence typing(MLST).Among these,STs,ST1,and ST7 belong to serotype 2 and are the major hazards of S.suis.in 1998 and 2005,two cases of SS2 human infection outbreak were reported in Jiangsu and Sichuan,China,causing 14 deaths and 38 deaths,respectively.

Prevention and Treatment of Chinese Herbal Preparation Yinqiaotiangan against Pathologic Model of Streptococcus suis Serotype II in Kunming Mice

[ Objectlve] This study aimed to investigate the antimicrobial effect of Chinese herbal preparation Yinqiaotiangan against Streptococcus suis serotype II in vivo. [ Method ] The prevention and treatment tests were conducted with Kunming mice weighing about 18 -22 g. In the prevention test, Kunming mice were inocu- lated with Streptococcus suis serotype II and simultaneously taken orally 0.5, 1.0 and 2.0 g/ml Chinese herbal preparation Yinqiaotiangan respectively for continu- ous 3 d, once a day; the incidence rate, mortality rate and protective rate were detected after 7 d. In the treatment test, Kunming mice were inoculated with Strepto- coccus suis serotype II to establish the Streptococcus suis serotype II pathogenic model, and then taken orally 0.5, 1.0 and 2.0 g/ml Chinese herbal preparation Yin- qiaotiangan respectively for continuous 3 d, twice a day; the mortality rate, cure rate and effective rate were detected after 7 d. [ Result ] Results of the prevention test showed that the protective rate in experimental groups was extremely significantly higher than that in control group （P 〈0.01 ）, while the incidence rate and mortality rate were extremely significantly lower than that in control group （P 〈0.01 ）. Results of the treatment test showed that the incidence rate in experimental groups was extremely significantly lower than that in control group （P 〈0.01 ）, the cure rate in 0.5 g/ml group was extremely significantly higher than that in 1.0 g/ml group and 2.0 g/ml group （P 〈 0.01 ）, the effective rate in 0.5 g/ml group was significantly higher than that in 1.0 g/ml group and 2.0 g/ml group （ P 〈 0.05 ）, with no significant difference from the positive group （P 〉 0.05 ）. [ Conclusion ] The pathologic model of Streptococcus su/s serotype II could be effec- tively prevented and treated by oral intake of low dose of Chinese herbal preparation Yinqiaotiangan in Kunming mice.

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.

猪链球菌靶向DC重组蛋白DC3pep-SDZ对斑马鱼的免疫保护性分析

为了探究本课题组前期构建的由猪链球菌(SS)的分泌型DNA核酸酶A(SsnA)、二氢硫辛酰胺脱氢酶(DLDH)和高亲和力锌摄取系统蛋白(ZnuA)3个毒力因子的优势细胞表位和树突状细胞靶向肽(DC3pep)串联而成的重组蛋白DC3pep-SDZ(SsnA-DLDH-ZnuA)对致病型SS攻击斑马鱼的免疫保护效果,本试验表达和纯化重组蛋白DC3pep-SDZ和SDZ,分别免疫AB系野生型斑马鱼,攻击致病型2、3和9型SS(SS2、SS3和SS9),计算存活率,采用苏木精-伊红(H.E.)染色法观察斑马鱼脑组织病理变化,实时荧光定量PCR(RT-qPCR)分析SS3感染斑马鱼后脑组织炎性细胞因子表达量变化。结果显示,诱导表达的重组蛋白DC3pep-SDZ和SDZ分子质量分别为44和42 kDa,2个蛋白均以可溶的形式表达。SS2、SS3和SS9攻击斑马鱼后,重组蛋白DC3pep-SDZ组和重组蛋白SDZ组斑马鱼存活率分别为50.0%、65.0%和60.0%,45.0%、47.3%和45.0%,两组间差异不显著(P>0.05),但与PBS对照组相比差异均极其显著(P<0.001)。H.E.染色镜检结果显示,重组蛋白DC3pep-SDZ组的斑马鱼被3种分型SS攻击后脑组织均无明显病理变化。RT-qPCR结果显示,重组蛋白DC3pep-SDZ组促炎细胞因子:与PBS对照组相比较IL-6、TNF-α和IFN-γmRNA表达量分别极显著(P<0.01)、极其显著(P<0.001)和极显著(P<0.01)下调,与重组蛋白SDZ组相比较IL-6和TNF-αmRNA表达量分别极显著(P<0.01)和显著下调(P<0.05);重组蛋白DC3pep-SDZ组抗炎性细胞因子:与PBS对照组相比较IL-10和TGF-β1 mRNA表达量分别极显著(P<0.01)和极其显著(P<0.001)上调,与重组蛋白SDZ组相比较TGF-β1 mRNA表达量显著上调(P<0.05)。结果表明,重组蛋白DC3pep-SDZ较SDZ具有更好的免疫原性,能产生SS2、SS3和SS9交叉免疫保护作用,同时还能够有效缓解斑马鱼感染SS3后的脑部炎症。

Presence of <i>Actinobacillus pleuropneumoniae, Streptococcus suis, Pasteurella multocida, Bordetella bronchiseptica, Haemophilus parasuis and Mycoplasma hyopneumoniae</i>in upper respiratory tract of swine in farms from Aguascalientes, Mexico

Respiratory diseases are one of the most important health problems in pig herds. The porcine respiratory disease complex (PRDC) is the term used to describe pneumonic diseases caused by multiple infectious agents that provoke weight loss in animals or death. In the PRDC multiple pathogens (bacteria and/or viruses) work in combination to induce this respiratory disease. Within this complex, Actinobacillus pleuropneumoniae, Streptococcus suis, Pasteurella multocida, Bordetella bronchiseptica, Haemophilus parasuis and Mycoplasma hyopneumoniae are the main bacterial pathogens involved in great economic losses to the swine industry. The aim of this work was to estimate the presence of A. pleuropneumoniae, S. suis, P. multocida, B. bronchiseptica, H. parasuis and M. hyopneumoniae in the upper respiratory tract of pigs in representative swine farms inAguascalientes,Mexico, using PCR technique. The study was performed in 14 swine farms. We obtained a total of 212 nasal swabs. Near 20% of samples were positive for A. pleuropneumoniae (located in the 79% of farms);17% were positive for S. suis (in 86% of farms), of these, 3% were S. suis serovar 2;30% were positive for H. parasuis (93% of farms);23% of the samples to P. multocida (in 79% of farms);and 19% to M. hyopneumoniae (in 64% of farms). B. bronchiseptica was not detected in this study. The results obtained show that bacterial pathogens of PRDC were present in the upper respiratory tract of pigs in all farms studied;therefore, these pathogens are widely disseminated in pig farms of Aguascalientes, Mexico.

Erythromycin Resistance of Streptococcus suis Isolates In Vivo

In order to study erythromycin resistance of Streptococcus suis under high or low concentration of selective drug pressure, Streptococcus suis strain LN was isolated from a diseased pig in 2005 and showed to be susceptible to erythromycin as determined by disc diffusion and tube dilution tests. In this study, clean level rabbits were divided into three groups of six rabbits each, including a prevention dosage group, a treatment dosage group, and a control group. After injection with S. suis strain LN, erythromycin （20 μg mL^-1） was taken orally in the prevention dosage group, erythromycin （5 mg kg^-1） was injected intramuscularly in the treatment dosage group, and no treatment was given in the control group. S. suis with intermediate resistance to erythromycin was isolated on the 5th day after infection from the prevention dosage group （5th PDG） and on the 7th day after infection from the treatment dosage group （7th TDG）. Both isolates were determined to be the constitutive macrolide-lincosamide-streptogramin B （cMLSB） resistance phenotype. The resistance gene ermB was detected in all of the isolates. The results suggested that both the 5th PDG and 7th TDG isolates had a mutation （A2372T） in the 23S rRNA gene. In addition, the 5th PDG isolates had a mutation in ribosomal protein L4 （detected as G268A） and a mutation in ribosomal protein L22 （A345C）; and the 7th TDG isolates had a C insertion at site 564. Each of these mutations is considered as a possible mechanism of erythromycin resistance in S. suis strain LN. This study demonstrated that erythromycin resistance was readily induced in S. suis at a low erythromycin dose creating selective pressure in vivo. Resistance appeared to be mediated by ribosome methylation, encoded by the ermB gene.

Identification of Antigens Common to Streptococcus suis Serotypes 2 and 9 by Immunoproteomic Analysis

Streptococcus suis is a Gram-positive pathogen that causes serious diseases in pigs. In addition to S. suis serotype 2 （SS2）, S. suis serotype 9 （SS9） is another prevalent serotype, which is frequently isolated from the organs of diseased pigs in China. An immunoproteomic-based approach was developed to identify antigens common to SS2 and SS9 for vaccine development. Cell wall proteins extracted from SS2 strain HA9801 were screened by two-dimensional Western blot using anti-SS2 sera, anti-SS9 sera, or pre-immune sera pooled from specific pathogen free （SPF） mice. Protein spots on preparative gels were excised and identified by matrix-assisted laser desorption ionization time-of-flight mass spectrometry, which led to the identification of four shared immunogenic proteins （arginine deiminase, translation elongation factor-Ts, o-acetylserine lyase, and 1-phosphofructokinase）. The genes encoding these four proteins from SS9 strain GZ0565 were cloned and their proteins were overexpressed in Escherichia coli BL21. Western blot analysis of these recombinant proteins using the convalescent serum of an SPF mini-pig inoculated with the SS2 strain, anti-SS2 sera, and anti-SS9 sera pooled from SPF mice further confirmed the immunogenicity of these proteins. These immunogenic proteins, which are encoded by genes that are reasonably conserved among SS2 and SS9 strains, could be developed as vaccine candidates.

The Mathematical Model for Streptococcus suis Infection in Pig-Human Population with Humidity Effect

In this paper,we developed a mathematical model for Streptococcus suis,which is an epidemic by considering the moisture that affects the infection.The disease is caused by Streptococcus suis infection found in pigs which can be transmitted to humans.The patients of Streptococcus suis were generally found in adults males and the elderly who contacted pigs or who ate uncooked pork.In human cases,the infection can cause a severe illness and death.This disease has an impact to the financial losses in the swine industry.In the development of models for this disease,we have divided the population into 7 related groups which are susceptible pig compartment,infected pig compartment,quarantined pig compartment,recovered pig compartment,susceptible human compartment,infected human compartment,and recovered human compartment.After that,we use this model and a quarantine strategy to analyze the spread of the infection.In addition,the basic reproduction number R0 is determined by using the next-generation matrix which can analyze the stability of the model.The numerical simulations of the proposed model are illustrated to confirm the results from theorems.The results showed that there is an effect from moisture to the disease transmission.When the moisture increases the disease infection also increases.

猪链球菌Sao-M和Ide_(Ssuis)蛋白的原核表达与反应原性分析

通过原核表达系统表达猪链球菌Sao-M和Ide_(Ssuis)基因,并分析其反应原性。根据GenBank数据库发表的序列,利用分子生物学软件设计了2对特异性引物,通过PCR扩增Sao-M和Ide_(Ssuis)基因,经测序分析后,分别克隆到pET28a(+)和pMAL-c2X,构建重组表达质粒pET28a:Sao-M和p MAL-c2X:Ide_(Ssuis),然后将鉴定为阳性的重组质粒分别转入宿主菌BL21和Rosetta2中用IPTG进行诱导表达,通过免疫印迹进行鉴定。实验表明,两种重组蛋白在原核系统中获得了高效的表达,并能与相应的阳性抗血清发生特异性反应。本研究为进一步探究Sao-M和Ide_(Ssuis)蛋白生物学功能及其在猪链球菌致病机制上的作用提供了依据。

S.suis 2溶血素SLY的分子克隆及溶血活性和免疫学特性研究

目的克隆并表达猪链球菌2型(S.suis 2)溶血素重组蛋白SLY,对其溶血活性及免疫学特性进行研究,为探讨SLY在S.suis 2感染中的致病机理及筛选有效的疫苗预防和控制猪链球菌病奠定基础。方法对S.suis2 05ZYH33全基因序列进行生物信息学分析,构建pET32a-sly原核表达质粒并诱导表达出S.suis 2重组溶血素SLY蛋白;采用高浓度尿素裂解包涵体和His-Tag亲和层析对重组SLY蛋白进行纯化并复性;免疫保护实验检验SLY的免疫保护作用。结果 SDS-PAGE显示70kD的SLY蛋白条带;重组SLY蛋白具有溶血活性并受多种因素的影响;SLY对感染S.suis 2的Balb/c小鼠有一定的免疫保护作用。结论优化原核表达体系可以有效提高SLY蛋白的表达量,经提纯并复性的重组SLY具有较高的溶血价,为进一步纯化及分析SLY蛋白的特性提供了必要的前提。