| In recent years,porcine Pasteurella multocida has been widely used in our country,and has become one of the main pathogenic bacteria.In this study,57 strains of Pasteurella multocida were studied by the method of capsular typing,genotyping and virulence test,and the immune protection test was carried out on 1 strains of attenuated strains,The main results were as follows:1.Fifty-seven strains of Pasteurella multocida were stored in the laboratory(Carter typing),genotyping(Harper classification).Carter typing of 32 strains of capsule type D,accounting for 56.14%;25 cases of capsular A,accounting for43.86%;not detected B,E and F.Harper classification was identified in 42 strains of L6,accounting for 73.68%;L3 type 13,accounting for 22.80%;there are 1 L1 type,L5 type 1;no detection of L2,L4,L7 and L8 type.This indicates that Pasteurella multocida is mainly Carter type A and type D in Chinese.The Harper genotype is mainly L6 and L3,and there are a few L1 and L5.The relationship between Carter typing and Harper classification was that all 32 Carter D types were Harper L6 and 25 strains of Carter A,including Harper L3 type 13,L6 type 10,L1 type 1 and L5 type 1strain.2.The virulence test showed that 25 strains of Carter type A had strong virulence,and LD50 was between 17 and 2.1 × 105 CFU.The most potent was PM-5,and the LD50 was not more than 9 CFU.32 strains of Carter D strains of virulence is generally weak,the LD50 between 2.0 × 104 ~ 4.8 × 107 CFU,which is the most virulent PM-15,the LD50 of 2.0×10~4CFU.According to Harper genotyping virulence comparison,Carter Type A Harper L6>Carter Type A Harper L3 Type>Carter Type D Harper L6 Type.Two strains of attenuated PM-18 and PM-37 were found in the strain of type 5(Harper L6)with LD50>4.8×10~7 CFU and 5.3×10~4 CFU,respectively.At the same time,1strains of type D(Harper type L6)toxigenic Pasteurella multocida strain TPM9 were found,and the LD50 was more than 2.6×106 CFU.Whether these 3 strains can be used as natural attenuated vaccine strains should be further studied.3.This study evaluated the safety of PM-18 attenuated strain as a natural attenuated vaccine strain.The results of the mouse safety test showed that the mice in the high dose vaccination group(9.6×10~7CFU)appeared temporary depression,loss of appetite and other phenomena,but returned to normal within 24 hours.Low dose group(9.6×10~5CFU)had no obvious clinical symptoms and pathological changes.The results of a single dose inoculation test showed that there were no obvious clinical symptoms and pathological changes after the large dose of intramuscular injection of piglets(6.2×10~9CFU/ head).The results of single dose repeated inoculation test showed that there were no obvious clinical symptoms and pathological changes after 2 high dose intramuscular injection of piglets(1.2×1010 CFU/head).4.22 to 25 day old piglets were inoculated with PM-18 attenuated strain for 2times(21 days interval,4.4×10~9 CFU/head/time),14 days after the second immunization with high dose and low dose D-type virulent strain PM-15 bacteria for abdominal challenge,the results show that PM-18 one of the piglets in the immunized group showed typical symptoms and died,the protection rate was 4/5;All the piglets in the blank control group had serious symptoms and all died.The results of ELISA antibody test showed that the serum antibody level(OD630nm)in the PM-18 immunized piglets was significantly higher than that in the control group(P <0.01)after the second immunization(35d).This indicates that PM-18 attenuated strains have the potential to be further developed as a natural attenuated vaccine. |
PDF Full Text Request