| ObjectiveThe objective of this essay is to clarify the distribution characteristics and pathogenicity of main serotypes and virulence factors of Streptococcus suis epidemic strains in Liaoning Province,exploring and analyzing the differences and correlations among virulence factors,pathogenic characteristics and pathological types of different serotypes.On the one hand,it provides a theoretical basis for exploring the pathogenic mechanism of Streptococcus suis.On the other hand,it provides a basis for establishing corresponding diagnostic methods,developing new drugs and vaccines,and formulating corresponding prevention and control measures.MethodsCharacteristics of prevalence and types of pathological changes are statistically analyzed from the samples which collected from the SS suspected case,such as lung,liver,spleen,brain and joint fluid,which came from 17 large-scale pig farms in Liaoning Province.The collected samples were preliminarily identified by isolation and purification culture,morphological characteristics observation,biochemical experiments and other bacteriological methods.According to the conserved genes and serotype specific genes of Streptococcus suis,the serotype of streptococcus suis isolated from Liaoning was identified.Statistical analysis was conducted on pathological types and serotypes of confirmed samples of Streptococcus suis cases,to analyze the correlation between different pathological types and serotypes,so as to determine the dominant serotypes of different pathological types of Streptococcus suis.The main virulence factors of SS of different serotypes are detected by using the virulence factor specific genes,and distribution and differentiation of the main virulence factors of different serotypes of Streptococcus suis are compared and analyzed.Through using mouse challenge test and pathology technique,the pathogenicity of different serotypes of streptococcus suis is observed,comparing and analyzing the differences from different serotypes of Pathogenicity.Results1.The main disease type,serum type and their changing trend of Streptococcus suis in Liaoning Province were identified.The main serotypes of Streptococcus suis strains in Liaoning Province were 1,2 and 7,which were different from other areas.In addition,there are some differences from popular serotypes in different periods.For example,in 2015,the detected serotypes were 1,2 and 7;in 2016,the detected serotypes were 2 and 7;in 2017,the detected serotypes were 1,2 and 7.Since 2017,the incidence and mortality of Streptococcus suis in Liaoning Province have been significantly reduced,which may be related to the change of serum type.2.The serotypes of Streptococcus suis isolated from different pathological types are statistically analyzed,and the results show that the acute septic blood type and arthritis type are SS2,the meningitis type are mainly SS1,and the suppurative lymphadenitis(lymph node abscess)type and other mild infections are mainly SS7.This indicates that the dominant serotypes of acute septic blood type,arthritis type,meningitis type and suppurative lymphadenitis Streptococcus suis are SS2,SS1 and SS7,respectively.3.The detection and analysis results of different serotypes of virulence factors show that most of SS2 possess 5-6 virulence factors,while SS1,SS7 and serotype negative Streptococcus suis only possess partial virulence factors.That once again proves that the virulence of SS2 is far larger than that of other serotypes,which is related to its virulence factor distribution.Also,it illustrates that the phenotype of SS2 virulence factor in Liaoning Province is different from that in other regions.The main virulence factor between SS2 and other serotypes is epf,which indicates that epf is an important virulence factor of Streptococcus suis.This result further supports the conclusion which other studies have proved that epf is an important virulence factor of Streptococcus suis and it can be used as an indicator of virulence of strains.4.Three strains of SS serotypes(1,2,7)prevalent in Liaoning province were tested for the pathogenicity of intraperitoneal and intracerebral inoculation in mice.The outcome shows that SS2 lead to the death of all mice,with the performance of acute and severe sepsis and meningitis.SS1 and SS7 cause the death of part of mice,with each organ damaged and lighter meningitis reaction,but as for mortality rate,SS1,with serious lesion severity,is higher than that of SS7,which means the pathogenicity of SS2 is the strongest,followed by that of SS1,then SS7 is the lightest one.Different serotypes have different damaging effects on organ,and SS2 shows more significant effects on organ damage than that of SS1 and SS7.SS1 shows significantly damage on brain tissue,while SS7 on liver and spleen.Experimental results of intracerebral inoculation show that the response degree of meningitis is significantly higher than that of intraperitoneal inoculation.Conclusions1.The main serotypes of Streptococcus suis strains in Liaoning Province are 1,2 and 7,which are different from that of other areas.SS2 has 5-6 virulence factors,while SS1,SS7 and serotype negative Streptococcus suis have only partial virulence factors,which proves that the distribution of virulence factors of different serotypes of Streptococcus suis is quite different.2.The dominant serotypes of Streptococcus suis in different pathological types are different.The dominant serotypes of streptococcus suis in acute sepsis type,arthritis type,meningitis type and suppurative lymphadenitis type were SS2,SS1 and SS7,respectively.3.The pathogenicity of SS2 is the strongest,followed by SS1,and SS7 was the lightest,which confirms that the pathogenicity of different serotypes of streptococcus suis is significantly different.Different serotypes have selective differences in the damage of infected animal organs,which indicates that Streptococcus suis serotype is associated with multiple pathological types of clinical manifestations. |
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