| In recent years,Streptococcus suis is a prevalent pathogen in our country,and has become one of the main pathogens which seriously harm the development of swine industry.In this study,the pathogen epidemiology virulence characteristics and biological characteristics of Streptococcus suis were systematically studied:1.Through separation and identification of Streptococcus suis(2014.09 ~2015.12)and statistical analysis combined with previous investigation(2011.01~2014.08),in recent years,772 Streptococcus isolates were cultured from 2521 lung samples collected from diseased pigs.During the 5-year period,the average isolation rate was 30.6%,making Streptococcus the most frequently isolated pathogenic bacterium from those lung samples.The results revealed that S.suis with 43.5% of the Streptococci isolates,had replaced Streptococcus equi subsp.zooepidemicus as the predominant agent.Among the strains investigated,serotype 2(53.3%)was most prevalent,followed by serotypes 7(10.4%),9(10.4%)and 1(1.5%).The results showed that in Henan and its neighboring provinces,streptococcus was the highest bacterial pathogen with the highest isolation rate,Streptococcus suis still plays an important role(43.5%),in Streptococcus suis serotype 2 was dominant(53.3%).2.The isolation rates in different years and months ranged from 23.5% to 45.5% and 25.9 to 41.9%,respectively.There were significant influences of sampling year and month on bacterial isolation(P<0.05).Streptococcus was isolated alone in 35.5% of the cases(274/772 isolates),and together with at least one or more other bacterial pathogens in 64.5% of the cases.Haemophilus parasuis(47.4%;236/498),Escherichia coli(35.3%;176/498),and Pasteurella multocida(20.9%;104/498)were isolated most frequently in association with Streptococcus,followed by Bordetella bronchiseptica(15.3%;76/498),and Staphylococcus aureus(6.2%;31/498),Salmonella enterica(6.1%;30/498)and Actinobacillus pleuropneumoniae(1.0%;5/498).The results showed that the occurrence of Streptococcus suis was seasonal,and the co infection with other pathogens was very serious.3.Isolation and identification of 49 strains of Streptococcus suis,including 26 strains of type 2,14 strains of type 7,and 9 strains of type 9,and the previous isolation and identification of 2 strains of group C Streptococcus equi subsp.zooepidemicus virulent.The results of mouse toxicity tests showed that group C strains showed the highest toxicity,followed by Streptococcus suis type 7,type 2 and type 9 strains.There were 3 strains of type 2?3 strains of type 7?3 strains of type 9 and 2 strains of group C were choosed from the most virulent(11 strains).Further toxicity test on pigs showed that 3 strains of type 2 and 2 strains of group C have typical clinical symptoms and pathological changes,1 strains of type 9 have typical clinical symptoms and pathological changes,3 strains of type 7 have not occur typical clinical symptoms and pathological changes.This shows that in our country the group C and type 2 have strong virulence,followed by type 7 and type 9.In addition,the virulence test results of mice were not completely consistent with pigs.4.M1 of group C and SS2-2 of type 2 were used as the representative strains to carry out the culture media screening test.Growth rate culture results shows that in different serotype strains in Tryptic soy agar howed that M1 of group C is greater than rate of SS2-2 of type 2 from five different solid medium,M1 of group C and SS2-2 of type 2 in Tryptic soy broth have a high level of viable bacteria from five different liquid medium.Further test in tryptic soy agar with 11 strains above howed that group C is greater than rate of type 2,type 7 and type 9,but type 2,type 7 and type 9 was no significant difference.Culture results in Tryptic soy broth howed that the highest colony-forming units for type 2,type 7,type 9 and group C strains are 6.4×108~1.0× 109CFU/ml which could be fermented in high density.There are different fermentation patterns between the group C and other stains isolates for 21 different carbohydrates,and even in the sameserogroup Streptococcus strains the difference exists.Susceptibility testing results show that all the strains Streptococcus strong poison strain is highly sensitive to?-lactam antibiotic.These tests screened out the best medium for pig streptococcus culture,at the same time,the biochemical characteristics,growth characteristics and drug sensitivity of 11 strains were compared,lay the foundation for the development of inactivated vaccine. |
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