| Streptococcus suis (S. suis) is an important pathogen of zoonosis, 35 differentserotypes (1-34 and 1/2) have been described. Serotypes 1, 1/2, 2, 7, 9 and 14 areconsidered to be more invasive than others. S. suis can be isolated from upperrespiratory tract, subclinical carrier animals are the most important source from whichthe bacteria are transmitted to sensitive pigs. S. suis can be divided intohighly-virulence, weakly-virulence and non-virulence. At present several potentialvirulence factors have been described, but the virulent of S. suis can't be determinedby the occurrence of these factors. Therefore, animal models still is a unique way toevaluate the virulent of S. suis.1. Carrier rate of Streptococcus suis in palatine tonsils of slaughterpigs in south of ChinaTwo multi-PCR assays was used for testing the presence of S. suis and its six majorserotypes from 401 palatine tonsils of slaughter pigs, collected in south of china 2006.Totally, S. suis existed in 154 (38.4%) tonsil samples. In these samples, 69 (17.2%) ispositive for serotype 2 (or serotypel/2); serotype 9, 35 (8.7%) samples; serotype 7, 9(2.2%) samples; and serotype 1 (or serotype 14), 3 (0.7%) samples. Moreover, someof these serotypes could be simultaneously tested in one tonsil sample, 18 (4.49%)samples were coinfected with serotype 2 (or serotype1/2) and serotype 9; serotype 2(or serotype1/2) and serotype 7, 6 (1.50%) samples; serotype 7 and serotype 9, 4(1.00%) samples; serotype 2 (or serotype1/2), serotype 7 and serotype 9, 3 (0.75%)samples. The prevalence ratio of S. suis appeared no significant diversity (p＞0.05)between different areas, was 35%～70%, except west of Guangdong province. In thisareas, the prevalence ratio of S. suis (18.3%) was more lower (p＜0.01) than others. 53 S. suis was isolated from all palatine t, onsils, 25 (6.23%) belong to serotype 2 (orserotype 1/2). 3 (0.75%) belong to serotype 9, 1 (0.25%) belong to serotype 7. 24(5.99%) belong to other serotypes, respectively. 286 samples matched in both PCRtest and bacterial examination S. suis. 108 samples positive in PCR but negative inbacterial examination and 7 samples dissimilar the other way around. This led to anagreement of 71.32% between both tests. The apparent prevalence indicated by PCRwas 25% higher than by in bacterial examination. These results showed that serotype1. 1/2, 2. 7, 9 and 14 coinfected in pig population in south china, and serotype 2 (orserotype1/2) was the dominant serotype.2. Genetype of Streptococcus suis isolated from palatine tonsils ofslaughter pigsTo investigate the distribution of virulence genes of 29 Streptococcus suis (SS)isolated from tonsils, 7 virulence genes were selected to be detected by PCR assay,namely the glutamate dehydrogenase gene (gdh), the suilysin gene (sly), theextracellular factor gene (ef), the muramidase-released protein gene (mrp), thefibronectin-binding protein gene (fpbs), the glyceraldehyde-3-phosphatedehydrogenase (gadph) gene and the virulence-associated sequence orf2. 25 serotype2 isolates presented 7 genetypes. 10 isolates (40%) carried all 7 virulence genes; 7isolates (28%) lost sly and ef; 4 isolates (16%) lost sly; one isolate lost orf2; oneisolate lost sly, ef and orf2; one isolate lost sly, ef and carried a large mrp gene; oneisolate lost sly, ef, mrp, fbps and orf2 five genes. 1 serotype 7 isolate lost ef and mrp. 3serotype 9 isolates lost sly, ef and mrp. The results showed the distribution of virulentgenes of streptococcus suis in China was complicated, and the prevalent strainsof S.suis serotype 2 was stains which have all 7 virulence genes.3 Characters of streptococcus suis serotype 2 and serotype 9 isolatedfrom dead pigsTwo pathogenic bacteria were isolated from 9 dead pigs in Guangdong provincebetween summer and autumn in 2005. The morphological and cultural charactersindicated that the isolates belonged to genus Streptococcus. The biochemistrycharacters of isolates was similar, and they couldn't be agglutinated by the Lancefieldgroup A～G latex diagnostic kit. Two isolates were identified by serotype-specificPCR, one of the isolates was streptococcus suis serotype 2 and another wasstreptococcus suis serotype 9. Moreover, genetype sly+ ef+ mrp+ was detected in isolateof serotype 2, but its virulence was low and infected mouse 6～15d post inoculated. Genetype sly- ef mrp- was detected in isolate of serotype 9, but it was high virulence tomouse, and its LD50 was 1.70×106CFU. It demonstrated that not only streptococcussuis serotype 2 but also streptococcus suis serotype 9 could cause pigs'streptococcusis in Guangdong province.4. Evaluating the virulence of different genetype Streptococccus suistype 2 isolates by Tibet mini-pig model3 Streptococccus suis capsular type 2 strains were selected to infect Tibet mini-pigs,in order to evaluate an experimental model with Tibet mini-pigs. 12 piglets wereallotted in 4 separated groups. Group A consisted of negative control animals whichreceived broth medium. Groups B. C, and D were intravenously challenged with 2mL of S. suis strains GZ06-122B, SH06-21D and HA9801, respectively. The strainGZ06-122B and SH06-21D was isolated from tonsils of slaughter pigs in south ofchina, and genetype were sly-/mrp-/ef- and sly+/mrp+/ef+. The strain HA9801 wasisolated from dead pig in Jiangsu. Pigs inoculated with strain GZ06-122B did notpresent clinical signs of a S. suis infection. Contamination in organs and bacterialblood circulation were rare and lesions were almost non-existent. Infection of pigswith S. suis strain SH06-21D (group C) and HA9801 (group D) caused severe clinicalproblems, animals infected with S. suis HA9801 were the most affected. Pigspresented with clinical signs such as high body temperature, lameness, nervoussymptoms, and even mortality. One week after inoculation, 1 pig died in group C and2 pigs died in group D. It can be concluded that S. suis strain HA9801 is most virulent,followed by SH06-21D and GZ06-122B. The results demonstrated that anexperimental model with Tibet mini-pigs can be used for discriminating the virulenceof different S. suis type 2 strains.
|
PDF Full Text Request