Prevalence of Streptococcus suis types 1 and 2 in domestic pigs in Australia and New Zealand

Using an indirect fluorescent antibody test, 54 per cent of 734 palatine tonsils of conventional pigs slaughtered in Australia and New Zealand were found to be infected with Streptococcus suis type 1 and 73 per cent of 959 were infected with S suis type 2. Variations in the prevalence of infection in pigs from different herds were thought to be due to differences in the sample sizes rather than to real differences in the prevalence between herds. The prevalence of infection with S suis was similar in pigs of either sex and in different age groups. Streptococcus suis type 2 was detected in the blood of 3 per cent of apparently normal pigs slaughtered at a meat processing plant. The presence of this organism in edible tissue may pose a health risk to consumers and meat-workers. Both S suis types 1 and 2 were detected in the vaginas and uteri of slaughtered pigs and the female reproductive tract could be another site for the carriage of infection. Piglets from sows with vaginas infected with S suis type 2 became infected earlier than piglets from sows with uninfected vaginas. No infected male reproductive tracts were detected and venereal transmission of S suis therefore appears unlikely. Three specific pathogen free herds were found to be free from infection with both S suis types 1 and 2. It is concluded that hysterectomy derived piglets are delivered free from infection, whereas some piglets born to sows with uterine and vaginal infections are either born infected or become infected at, or soon after, birth.     

Experimental infections of mice and pigs with Streptococcus suis type 2.

Five inbred strains of mice were tested for their susceptibility to Streptococcus suis type 2 including the type strain, two isolates from meningitis in pigs and two isolates from tonsils of clinically healthy pigs. C57BL/6, ICR and ddY strain mice showed lower susceptibility to all strains of S. suis type 2 than BALB/c and SS strain mice. The type strain and the isolates from diseased pigs produced septicaemia and meningitis in BALB/c and SS mice inoculated with 10(8) colony forming unit of the bacteria and 60 to 100% of these infected mice died. On the other hand, mice inoculated with the isolates from healthy pigs showed mild clinical signs but none of them died. In BALB/c mice which died or developed nervous signs, the purulent meningo-encephalitis, myocarditis, ophthalmitis, labyrinthitis and otitis media were observed. S. suis type 2 antigen was demonstrated in these lesions by immunoperoxidase staining using rabbit S. suis type 2 antiserum. These results were similar to those in the experimentally infected pigs with these virulent and avirulent strains against mice. These results indicate that BALB/c and SS strains of mice are useful as an experimental model of S. suis type 2 infections in pigs, and that there are virulent and avirulent strains against mice and pigs among the strains of S. suis type 2.     

Experimental exposure of young pigs using a pathogenic strain of Streptococcus suis serotype 2 and evaluation of this method for disease prevention.

Control of Streptococcus suis infections and associated disease have proven to be a difficult challenge under most farm conditions. The objective of this study was to experimentally expose young pigs with a pathogenic strain of S. suis serotype 2 as a means of controlling the disease in a commercial swine farm. Prior to the start of the study, the pathogenic S. suis strain responsible for mortality in the farm was identified and used to experimentally inoculate baby piglets. Over a 3-week period, groups of pigs were selected (100 pigs/wk) and divided into 2 groups: control (50 pigs/week) and experimentally exposed (50 pigs/week). Pigs in the experimentally exposed group were inoculated at 5 d old by tonsillar swabbing with the pathogenic S. suis farm isolate. The effect of exposure with this pathogenic strain was evaluated during the nursery and finishing stages and was based on: morbidity (pigs with central nervous signs (CNS) and/or lameness), mortality and number of treatments required by pigs that had either CNS or lameness. The relative risk (RR) of acquiring disease due to S. suis infection was also calculated. Results showed that morbidity in the experimentally exposed groups was lower than in the control group and these results were statistically different (P = 0.006). Experimentally exposed pigs also showed a statistically significant reduction in lameness problems (P = 0.012), but not in CNS (P = 0.20) or mortality (P = 0.59). Pigs in the control group had an increased RR of 4.76, 8.77 and 2.7 for morbidity, to have lameness or to have CNS signs, respectively. In conclusion, experimental exposure of young pigs with the farm's pathogenic S. suis strain at a young age, had a positive effect in reducing clinical signs characteristics of S. suis infection. This method constitutes a novel approach to the control of S. suis infections in swine farms.     

Immunisation of pigs with killed cultures of Streptococcus suis type 2

Ten intravenous inoculations of 10(10) formalin-killed pathogenic Streptococcus suis type 2 stimulated detectable levels of opsonic antibody and a strong protective response against intravenous challenge with 10(9) viable S suis type 2 of the same strain. Heat-killed organisms did not stimulate a protective response, even though the type-specific antigen was intact and opsonic antibodies were induced. When the number of formalin-killed organisms in the inoculum was increased 10-fold, one inoculation was insufficient to stimulate a protective response, but two inoculations protected pigs against intravenous challenge with live, pathogenic organisms. Four-hour and overnight cultures were equally immunogenic, and the response was not enhanced by either Freund's incomplete adjuvant or aluminium hydroxide gel adjuvant.     

Studies of Streptococcus suis type 2 infection in pigs

Investigations into the immunology, pathogenesis and epidemiology of Streptococcus suis type 2 infections were carried out in experimental pigs and in naturally-occurring field outbreaks of disease. The capsular polysaccharide from Str. suis type 2 was shown to induce opsonic antibodies in pigs when injected with Freund's incomplete adjuvant, but difficulties encountered in experimental production of the disease prevented a study of their protective effects. Problems with the bactericidal tests led to an investigation of other assays for antibodies against Str. suis type 2, namely, a phagocytic test with pig neutrophils, a mixed reverse passive antiglobulin haemagglutination test and an indirect haemagglutination test. There was evidence that with modifications both the latter tests would be useful. Transmission studies in 39 conventionally-reared and 7 hysterectomy-derived, colostrum-deprived pigs yielded interesting results with regard to the distribution of the organism in relation to the disease process. Tonsil carriage in clinically-healthy pigs was demonstrated after experimental and natural infection. Detectable carrier rates varied between 0 and 59%. The organism was shown to persist in the presence of circulating opsonic antibodies and in pigs on penicillin-medicated feed. Attempts to isolate the organism from the genital tract were unsuccessful. Medicated early weaning and classical SPF techniques applied to infected herds appeared to be effective in producing pigs free from Str. suis type 2 infection.     

Streptococcus suis isolated from pigs in Finland

A total of 58 Streptococcus suis strains were isolated from deceased pigs submitted to the National Veterinary Institute, Regional Laboratory in Kuopio, Finland, over a 3 1/2 year period, most frequently from cases of pneumonia. The bacteria were isolated from cases of meningitis, sepsis, rhinitis, endocarditis and abortion. S. suis was also isolated from nasal cavity, lung and brain of some sick piglets without signs of inflammation. Further S. suis was detected in 12 out of 107 tonsils of healthy fatteners tested. S. suis strains were identified by biochemical methods followed by typing. The most common capsular types were 7, 3 and 2, respectively. Only one type 1 strain and no types 6 and 9 strains were found. All S. suis strains tested were sensitive to penicillin and ampicillin.S. suis is not uncommon in Finnish pig herds. S. suis may be regarded as a potentially pathogenic organism which under certain predisposing conditions may cause serious disease.     

上海地区31株2型猪链球菌的分离鉴定及其耐药性分析

猪链球菌病是由猪链球菌引起的一种重要人畜共患病,尤其是猪链球菌2型,不仅对猪的致病性最强,而目可感染特定人群并致死,给人类公共卫生和养猪业带来巨大影响。本研究采集临床症状疑似2型猪链球菌感染猪的全血及内脏器官,通过观察菌落形态及培养特征,筛选出可疑样品,纯化培养并进行PCR鉴定,筛选到31株2型猪链球菌,最后用纸片扩散法对临床分离到的2型猪链球菌菌株测定其耐药性,结果显示对5种药物耐药率分别为：80%（AM）、68%（GM）、84%（CHL）、52%（SXT）、55%（CIP）。试验结果表明分离的31株2型猪源性链球菌,均为多重耐药株,且青霉素类药物的耐药性较为严重,这为临床在治疗2型猪链球菌病提供了合理的指导作用。     

Immunisation of pigs with live cultures of Streptococcus suis type 2

Repeated intravenous injections of pigs with live virulent cultures of Streptococcus suis type 2 stimulated a strong protective response against subsequent challenge. This protection was transferred passively to susceptible pigs by the inoculation of sera from protected pigs. A strong protective response was also stimulated by repeated inoculations of live cultures of non-pathogenic isolates. The protective response did not eliminate S suis type 2 organisms already established in the tonsils or joints, nor prevent the establishment of subclinical infection in the tonsils.     

Rapid detection of Streptococcus suis serotype 2 in weaned pigs

A survey to detect Streptococcus suis serotype 2 in 1,716 weaned pigs was done in Quebec. Forty-nine sow herds were included in this survey: in 26 herds, S suis serotype 2 had been isolated during the preceding 12 months and in 23 herds (control), the organism had not been detected during a previous study. Swab specimens of the nasal cavity and tonsils of pigs were obtained for bacteriologic culture, and S suis serotype 2 was easily detected by the use of brain-heart infusion agar containing a Streptococcus-selective supplement and 5% goat antiserum raised against S suis serotype 2. After measurement of the diameter of the precipitation zone of 539 isolates, a slide agglutination test was performed to identify the S suis serotype 2 isolates. The mean precipitation zone diameter obtained for group S suis serotype 2 was larger (P less than 0.001) than that for the group designated as "others". With slide agglutination test results as reference and on the basis of discriminant analysis to stimulate detection of S suis serotype 2, 93.1% of all isolates were correctly classified, using the precipitation zone diameter as unique classification criterion. Relative specificity was 94.5% and relative sensitivity was 88.7%. Use of the precipitation zone diameter on a quantitative basis led to the proposal of a simple and reliable technique to screen swine herds for S suis serotype 2 in weaned pigs. Nasal and tonsillar swab specimens were obtained and analyzed concurrently for S suis serotype 2. The organism was found in both sites in only 20.4% of 103 carrier pigs.(ABSTRACT TRUNCATED AT 250 WORDS)     

Detection of virulent strains of Streptococcus suis type 2 and highly virulent strains of Streptococcus suis type 1 in tonsillar specimens of pigs by PCR.

We developed a PCR assay for the rapid and sensitive detection of virulent Streptococcus suis type 2 and highly virulent S. suis type 1 in tonsillar specimens from pigs. The PCR primers were based on the sequence of the gene encoding the EF-protein of virulent S. suis type 2 strains (MRP+EF+) and highly virulent S. suis type 1 strains (MRP(s)EF+) and of the EF protein of weakly virulent S. suis type 2 strains (MRP+EF). The latter strains give rise to larger PCR products than the virulent strains of S. suis type 1 and 2. A positive control template was included in the assay to identify false negative results. The PCR was evaluated using tonsillar specimens from herds known (or suspected) to be infected and herds without an S. suis history. The results obtained with the PCR assay were compared with the results obtained with a newly developed bacteriological examination. In this bacteriological examination we were able to identify the EF-positive strains directly in the tonsillar specimens. From the 99 tonsils examined, 48 were positive in the PCR and 51 negative. All specimens from which EF-positive S. suis strains were isolated were also positive in the PCR assay. Three samples were positive in the PCR, but negative by bacteriological examination. The results demonstrated that the PCR is a highly specific and sensitive diagnostic tool for the detection of pigs carrying virulent strains of S. suis type 2 and highly virulent strains of type 1. Application of the assay may contribute to the control of S. suis infections.     

Production of muraminidase-released protein (MRP), extracellular factor (EF) and suilysin by field isolates of Streptococcus suis capsular types 2, 1/2, 9, 7 and 3 isolated from swine in France

A total of 323 isolates of Streptococcus suis recovered from diseased or healthy pigs in France were serotyped. The presence of virulence-related proteins, Muraminidase-Released Protein (MRP), Extracellular Factor (EF) and Suilysin was also studied in 122 isolates of capsular types 2, 1/2, 9, 7 and 3 to evaluate their implication in virulence of S. suis. Capsular types 2, 1/2, 9, 7 and 3 were the most frequently detected (93%), with 69% for the capsular type 2 alone. Capsular types 2, 1/2, 9, 7, 3, 1, 4, 8, 18, 10 and 12 were isolated from diseased pigs, whereas types 2, 7, 9, 1/2, and 3 originated from the nasal cavities or tonsils of healthy animals. Most of the S. suis type 2 isolates recovered from diseased pigs carried MRP+ EF- Suilysin- (46%) or MRP+ EF+ Suilysin+ (28%) phenotypes. The MRP+ EF- Suilysin- phenotype was also detected in 67% of S. suis type 2 strains isolated from healthy pigs. The production of the virulence-related proteins was less frequently found in S. suis types 1/2, 9, 7 and 3 recovered either from diseased or healthy pigs. In this study, all the capsular type 1/2 strains were MRP+ EF- Suilysin- and all the S. suis type 7 harboured an MRP- EF- Suilysin- phenotype. The MRP- EF- Suilysin- phenotype was found in S. suis types 2, 3, 7 and 9 isolated from septicaemia, meningitis, pneumonia, and pleurisy. These results suggest that the presence of these proteins should not be used as a single condition for classifying the virulence of a field isolate in France.     

Experimental infection of specific pathogen free piglets with French strains of Streptococcus suis capsular type 2.

A standardized model of Streptococcus suis type 2 infection in specific-pathogen-free piglets, housed in high-security barns, was used to compare the virulence of 3 French field strains of S. suis serotype 2 isolated from tonsils of a healthy pig (strain 65) or from diseased pigs (meningitis, strain 166', or septicemia, strain 24). In one of the 2 trials, 7-week-old pigs, in 3 groups of 8, were inoculated intravenously with 2 x 10(8) colony-forming units of S. suis type 2. In each group, 1 uninfected animal was a sentinel. Eight animals were also used as negative control group. The experiment was repeated under similar conditions with strains 65 and 166'. Virulence differed markedly among these S. suis strains when clinical signs, zootechnical performances, lesions, and bacteriological data were analyzed. Strain 65 did not induce clinical signs in inoculated pigs. In contrast, pigs infected with the other 2 strains exhibited clinical signs and typical lesions of S. suis type 2 infections. Differences in virulence were also observed between the 2 virulent strains. Sentinel animals exhibited the same manifestations as those recorded in inoculated piglets. Results were similar in the second trial, indicating that under the present experimental conditions, results were reproducible. The standardized conditions described in this study could be a useful tool to further study about the S. suis infection.     

IgA1 protease contributes to the virulence of Streptococcus suis

Streptococcus suis (S. suis) is a major swine pathogen and emerging zoonotic agent. However, the current understanding of the S. suis pathogenesis of infection remains limited. In the present study, the contribution to the pathogenesis of S. suis was evaluated on IgA1 protease (or iga gene), which has been regarded as a virulence factor of gram-negative pathogenic bacteria and of certain gram-positive pathogenic bacteria. In contrast to the wild type (WT) strain of S. suis serotype 2, the isogenic iga mutant (Δiga) constructed by allelic replacement showed significantly decreased lethality to pigs. The present study suggests that IgA1 protease might contribute to S. suis pathogenesis.     

猪链球菌病双重PCR诊断方法的建立

根据猪链球菌2型荚膜多糖和马链球菌兽疫亚种类M蛋白的保守区序列分别设计了2对简并引物,建立了一种能同时检测猪链球菌2型和马链球菌兽疫亚种的双重PCR方法。结果显示,该双重PCR能从100个细菌的混合纯培养物中扩增出2条目的片段。而且可以直接从病料组织中检测到相应的病原菌。用建立的双重PCR方法和细菌分离培养法平行检测人工感染的组织病料,PCR方法与细菌培养法的阳性检出率基本一致,但PCR方法的特异性好、敏感性高,简便易行,可以用于猪链球菌病的流行病学调查和实验室的快速鉴别诊断。     

Intestinal translocation of Streptococcus suis type 2 EF+ in pigs

Sepsis with subsequent multisystem organ failure after translocation of bacteria from the gut is a serious risk associated with stress situations. We showed that intestinal bacterial translocation could be one of the pathways for pathogenic Streptococcus suis infections in the pig. In 24 piglets weighing 10-14 kg, free of the extracellular factor (EF+) producing phenotype of S. suis serotype 2, a silicon canula was placed in the proximal jejunum to enable intestinal inoculation and bypassing the upper alimentary tract. The pigs were individually housed. After stress induction in 18 pigs by means of a truck drive in individual cages for 1h, pigs were inoculated through the intestinal canula either with S. suis type 2 EF+ or with growth medium only, and put back in their original housing. The six not transported pigs were also inoculated with the same strain. To prevent oral self-infection, faeces were collected in a bag that was glued around the anus. Clinical and behavioral symptoms were recorded for 72 h post inoculation, and then the animals were sacrificed for pathological and bacteriological examination. In three animals, the inoculation strain was re-isolated from mesenterial lymph nodes and typically affected organs. No S. suis type 2 EF+ was detected by specific polymerase chain reaction (PCR) in any of the tonsil-swabs and -homogenates. We concluded that infection of the organs had taken place after bacterial translocation out of the gut and that the intestinal tract can be a porte d'entree for S. suis type 2 EF+.     

Passive immunization of pigs against experimental infection with Streptococcus suis serotype 2

The safety and protective efficacy of a horse antiserum raised against inactivated whole cell preparations of Streptococcus suis serotype 2 was investigated in pigs by experimental challenge. The antiserum was evaluated in two similar experiments each comprising 12 4-week-old pigs treated with 6 ml of antiserum the day before challenge and four pigs used as challenge controls. Pigs were infected by subcutaneous injection with approximately 10(11) colony forming units of S. suis serotype 2. Clinical disease in the pigs that could be attributed to infection with S. suis was reduced from 88 to 35% (P = 0.015). The percentage of pigs with lesions that could be associated with S. suis was reduced from 88 to 22% (P = 0.002) and isolation of S. suis serotype 2 was reduced from five (63%) out of eight pigs in the combined challenge control groups to 3 (13%) out of 23 pigs in the combined treatment groups. These results indicate that passive immunization of pigs may be a way to reduce or control S. suis serotype 2 infections in pigs.     

Bacterial colonization and invasion in pigs experimentally exposed to Streptococcus suis serotype 2 in aerosol

A recently developed porcine model for aerogenous infection with Streptococcus suis serotype 2 was applied in a study of the phases of bacterial colonization and initial invasion. Eighteen pigs were exposed to aerosolized S. suis serotype 2 after pre-exposure to mild acetic acid in aerosol. The animals were killed consecutively within the first six days after challenge. After death, all animals were necropsied and examined by bacteriology, histopathology, and immunohistochemistry. Systemic infection was established in four out of 18 animals exposed to S. suis serotype 2. All systemically infected animals developed clinical signs and lesions typical of the infection. In four additional animals, subclinical infection was demonstrated by re-isolation of S. suis from the palatine tonsil. However, in all 18 challenged animals, immunohistochemistry demonstrated S. suis serotype 2 antigen in the palatine and/or nasopharyngeal tonsils. In all four systemically infected animals, S. suis serotype 2 antigen was also found in the mandibular lymph node. These observations point towards the tonsils as possible portals of entry for S. suis serotype 2 with subsequent lymphogenous spread. Thus, the present findings parallel the proposed pathogenesis for S. suis serotype 1 infection in pigs.     

Streptococcus suis serotypes associated with disease in weaned pigs

Streptococcus suis was recovered from 9 outbreaks of septicaemia and meningitis in weaned pigs between 1979 and 1983. Fifteen isolates from 7 outbreaks were identified as S. suis type 9, and 3 isolates from 2 outbreaks as S. suis type 2. Three further isolates of S. suis type 2 and an isolate of S. suis type 3 were recovered from cases of bronchopneumonia in weaned pigs from 4 other piggeries.     

Experimental airborne transmission of Streptococcus suis capsular type 2 in pigs.

Experimental airborne transmission of Streptococcus suis type 2 was studied in specific pathogen free piglets. Forty piglets were allotted to five groups of eight 7-week-old animals and housed in three separated units. Negative control pigs (group 1) were housed in unit A and infected batches were housed in units B (group 2) and C (groups 4). In units B and C, non-inoculated groups (groups 3 and 5, respectively), 40 cm distant from the respective inoculated group and without any physical contact between them, also took place. Six animals of groups 2 and 4 were inoculated intravenously with 2 x 10(8) colony forming units (cfu) of a mild and a high virulent S. suis strains, respectively. The remaining animals in these groups and pigs from groups 1, 3, 5 received broth medium in the same way. Differences among virulence of S. suis capsular type 2 were observed in inoculated pigs of groups 2 and 4. Pigs from group 2 became carriers, showing only mild symptoms. By contrast, animals from group 4 presented an acute form of the disease. All the indirect contact pigs in groups 3 and 5 had S. suis in palatine tonsils from day 6 after the infection and they presented clinical manifestations similar to those observed in experimentally infected pigs. Two direct contact animals were also contaminated in the upper respiratory tract but surprisingly they did not show any symptoms. Airborne transmission of S. suis in experimentally pigs was demonstrated in the present study. Indirect infections, as described in this study, are a more realistic way to infect pigs than other experimental procedures and may be used to further study the pathogenesis of the infection caused by this important pathogen.     

Cloning, expression and characterization of a cell wall surface protein, 6-phosphogluconate-dehydrogenase, of Streptococcus suis serotype 2

Streptococcus suis type 2 is a pathogen responsible for diverse diseases in both pigs and humans. In order to understand the pathogenesis of the S. suis type 2 infection, the gene encoding a cell surface protein, 6-phosphogluconate-dehydrogenase (6PGD) of S. suis type 2 was cloned and sequenced, and recombinant 6PGD protein (r6PGD) was produced in a prokaryotic expression system. Sequence analysis of the cloned 6 pdg gene showed 82% similarity with Streptococcus pneumoniae 6 pdg at the nucleic acid level. Western blotting using r6PGD-specific antiserum confirmed the cell surface location of the 6PGD protein of S. suis type 2. The role of 6PGD in S. suis type 2 pathogenesis as an adhesin and its immunogenicity in mice was further investigated. The results showed that the recombinant protein interfered with the adhesion of S. suis type 2 to Hep2 and HeLa cells by 72% and 66%, respectively. Immunization of CD-1 mice with r6PGD increased the protective efficacy by 80% following intraperitoneal administration of a lethal dose of S. suis type 2. Immunization of CD-1 mice with r6PGD elicited a significant protective immune response, which demonstrated the importance of 6PGD to bacterial pathogenesis. Identification and characterization of the role of S. suis type 2 6PGD in adhesion and immunogenicity will allow us to use this protein to develop new antimicrobial therapies and/or vaccines.