In order to clarify the pathogen which caused the neurological symptoms in fattening pigs from a pig farm of Tianjin as well as its characteristics and genetic characteristics,in this study,8 brain tissue samples of diseased pigs were inoculated for bacterial isolation.After morphological observation,PCR amplification of gdh gene and cps2J gene and sequence analysis were performed on the isolated strains.Finally,the isolated strain of all 8 samples was identified as the same SS2,named TJS75.The pathogenic characteristics of the SS2 isolates were analyzed using various methods,including growth curve determination,hemolytic test,adhesion and invasion experiments,and animal pathogenicity experiments.The results showed that the TJS75 strain could reach the logarithmic growth phase after TSB culture for 6 to 15 hours of in vitro cultivation and had a disintegrating effect on sheep red blood cells(RBC),and could adhere to and invade PK-15 cells(the adhesion rate and invasion rate were 5.16%and 7.90%,respectively).The pathogenicity test results showed that each group of BALB/c mice inoculated with TJS75 exhibited varying degrees of clinical symptoms such as delayed movement,shortness of breath,lethargy and nerves.Moreover,the LD 50 of TJS75 strain on BALB/c mice was 2.15×107cfu/mL.Using high-throughput sequencing,analysis and virulence gene prediction to determine the genetic characteristics of strains.The results showed that the total genome length of TJS75 strain was 2 368 195bp,with a GC content of 40.88%and containing 2 229 coding genes.A total of 1822 1830,and 1077 genes were annotated in the GO,COG and KEGG databases.The 16S rRNA gene sequence of TJS75 strain was highly related to the highly virulent SS strains 98HAH33 and 05ZYH33,which were isolated in China.The predicted results of virulence genes showed that TJS75 strain contained 499 virulence related genes(encoding 173 virulence related factors).According to its functional classification,the functions of these virulence related factors included adhesion and invasion,hemolysis,promoting iron transport,participating in the synthesis of autolytic enzymes,degrading collagenase,and participating in sialic acid synthesis.This study would provide a scientific basis for further research on the pathogenic mechanism of SS serotype 2 strain TJS75.
Streptococcus suis type 2isolation and identificationpathogenicitygenetic characteristics
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