| Streptococcus suis (S.suis) is an emerging zoonotic pathogen causing severe infections in pigs. According to the diversity in capsular polysaccharides (CPs) of S.suis, 29 serotypes of S.suis have been identified. In additon, some S.suis strains do not agglutinate with any of the typing antisera directed against the existing serotypes and are identified as non-typable isolates.1. IDENTIFICATION OF A NOVEL SEROTYPE STREPTOCOCCUS SUIS CAUSED MENINGIITIS IN PIGLETSFrom March to May 2013, pandemic meningitis was spread in multiplex large-scale pig farms in Jiangsu province. Susceptible population of this epidemic is the 30-day-old piglets, with a total morbidity of 35%. The fatality of infected piglets could reach 90%. The infected piglets showed obvious neurologic symptoms including tetraplegia, circle-walking and single side neck-crooking. No obvious pathological changes were found by autopsy except the severe piamatral congestion. The strain CZ130302 was identified as the S. suis, but non-typable under the analysis of the characters of the strain, developments of the PCR assays for 16S rRNA and gdh. The capsule was observed by TEM. Serotype identification of Multiplex PCR was operated as previous description, no positive result was observed in all 33 serotypes. On the other hand, agglutination test of isolate CZ130302 showed negative reactions with the serums of all 33 serotypes. In complementary agglutination tests, the serum of CZ130302 also demonstrated the no matched with the all reference strains. The LD50 values for strains CZ 130302 was 2×106 CFU/mouse. In groups challenged with 5×105 CFU/mouse (CZ130302), more than 60% (8/10) of the mice displayed neurological symptoms, and many survivors had sequelae, containing tetraplegia, paraplegia, neck-crooking, circling, etc. The results of pathological sections demonstrated the obvious Cells cuffing, neuronophagia, liquefaction of neuron and shrinkage of neuron. The fatality rate of CZ130302 was 8/10, more than the virulent serotype 2 S.suis P1/7(1/10) or HA9801(2/10). The bEnd.3 cells adhesion for strains P1/7 and CZ130302 was very closed (P<0.01), the HEp-2 cells adhesion for strain CZ130302 was significantly lower than strain P1/7 (P< 0.01), and not significantly different from strain HA9801. PCR assays showed the serotype 35 encoded 6 common virulence genes, including gdh, orf2, dltA, pgdA, srtA and SspA, was completely different from traditional virulent strains of S. suis (mrp+/epf+/sly+).2. GENETIC ANALYSIS OF THE CAPSULAR POLYSACCHARIDES SYNTHESIS IN THE NOVEL TYPE STRAINThe diversity of virlence is associated with the difference of the serotypes in S.suis. At present, the typing system of S.suis are identified on the basis of the antigenicity of their capsular polysaccharides (CPs). Genetic analysis of whole cps genes clusters of all serotypes was performed in this study. The result of comparative genomics showed that the cps gene cluster of CZ130302, which has never been found, was an unfamiliar one. Especially, the cpn60, recN, sodA and wzy, wzx, acetyltransferase genes of strain CZ130302 are phylogenetically distinct from other 33 serotypes strains, including the 32,34 serotypes and 20,22,26,33serotypes.The DNA sequence was deposited in GenBank under accession number KJ669337. Most of the capsular polysaccharides synthesis (CPS) genes are oriented in the same direction. The genes involved in the regulation and processing of capsular polysaccharides (CP), cps A, cpsB, cpsC, and cpsD (designated wzg, wzd, wze, and wzh, respectively, in the bacterial polysaccharide gene database, located on the 5’-side of the clusters.23 homology groups (HGs) were commented and the 4 HGs were unknown. The cps gene cluster of CZ130302 also contain genes encoding putative flippase(wzx) and polymerase (wzy), acetyltransferase (Chz-J), glycosyltransferase as well as various sets of glycosyltransferase genes, including an initial sugar transferase gene.The housekeeping genes Chz-M and Chz-O were performed as detecing the new serotype S.suis in the Mulitiplex PCR assays. The reference serotype strains was proofed and the Chz-M primers were negtive with all the strains.64 non-typable S.suis isolates from the storage of our lab were detected by above PCR and serology typing method. A total of 3 isolates (HN136, AH681 and CZ110902) separated from diseased pigs belonged to the novel serotype. The strain AH861 was an acapsular strain under TEM. The LD50 value for CZ110902 were 2.433 ×106 CFU/mouse.All 4 isolates were characterized using MLST. Two isolates of serotype 35 were classified as ST 383, and showed strong pathogenicity in swine and mouse model. Avirulent strain AH681 was classified as ST 475. The MLST data of another avirulent strain, HN136, which was regarded as a non-typable strain before, was submitted previous to our study and classified as ST 264. None of these three STs could be grouped in any clonal complexes (CC) according to eBURST analysis... |
PDF Full Text Request