| Aeromonas veronii is an important pathogen that can infect fish and many kinds of mammals, including human beings. It has been listed as one of quarantine items on food safety by some countries, because of the increasing harm. But the research about Aeromonas veronii is relatively less. To provide theoretical guidance for the identification of Aeromonas veronii, some biological characteristics were studied by using Aeromonas veronii JLL-1 strain isolated from one carp infected with disease as experimental materials in this sudy. Considering the advantages of inactivated vaccine, such as simple preparation and good immune effect, the inactivated vaccine of JLL-1 strain was prepared and its vaccine effects were observed.Firstly, some biological characteristics of JLL-1 strain were studied. The results showed that JLL-1 strain was a Gram-negative and short rod bacterium. The second growth phenomenon of JLL-1 was observed in liquid LB medium and it could grow well in a variety of media,such as EMB medium, BS medium and SS medium. JLL-1 strain had high tolerance to the temperature(25 ℃- 42 ℃), pH( 6-10) and concentration of NaCl( 0%- 4%).The results of drug sensitivity test indicated that JLL-1 was sensitive to 16 kinds of detection drugs, accounting for 69.57%(16/23),medium drugs and resistance drugs accounted for 17.39%(4/23)and13.04%(3/23) of the detection drugs, respectively. The median lethal dose(LD 50) of JLL-1 strain was 3.98×104CFU / mL and the symptoms of infected fish showed hemorrhage in fin and gill, hyperemia in intestine and acute death.The experimental group and control group(PBS) were randomly selected 10 fish used to collect blood at 0, 1, 2, 3 and 4weeks after being vaccinated.And part of them were used for testing phagocytic activity of leucocytes and the rest part of blood were prepared for serum used to examine various immune parameters.The results suggested that inactivated vaccine of JLL-1 strain could effectively enhance immunity of koi.The activity of acidic phosphatase(ACP) rose significantly at 1st week after immunization, reached the peak value on 2nd week(182.004U/L) and decreased after two weeks, but it was still higher than those in the control group.The activity of alkaline phosphatase(AKP) firstly decreased and then rose, but still lower than preimmunization.The SOD levels markedly increased, then reached the peak value(224U / mL) on 2nd week after immunization and decreased after two weeks, but still higher than control group.There was a positive correlation between phagocytic index(PI) and phagocytic percentage(PP).PI ascended consistently and reached maximum(2.9) on 3rd week and phagocytic percentage PP alsom reached maximum(36.67%) in the same week. Bactericidal activity of serum was kept at high level form 1st to 4th week after immunization, and the bacterial survival index was 59.42, 36.57, 8.23 and 46.49 respectively.The antibody titer of the experimental group rose consistently, reached to the maximum value(1: 1280) on the 3trd week, and decreased after three weeks, but control group was still 1:40. The challenge test was performed at four weeks post-immunization, and the results showed that the relative immune protection rate was 88%. |
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