| At present,traditional decontamination method is still the main measure to control pullorum disease.With the abuse of antibiotics,bacterial drug resistance is increase seriously.Vaccine immunization becomes one of the best auxiliary methods for pullorum disease decontamination.But so far,our country has not yet developed a available vaccine for pullorum disease,therefore,to find effective substitutes is urgent.Salmonella Enteritidis live vaccine,as the only approved Salmonella vaccine for chickens in China,is widely used in the prevention and control of Salmonella Enteritidis.Previous studies have shown that the live Salmonella Enteritidis vaccine has a good cross protection effect against Salmonella Pullorum infection in adult chickens after three immunizations at 1 day,6 weeks,and 16 weeks.However,Considering that Salmonella Pullorum mainly affects chicks aged 2~3 weeks,and there is no research indicated the cross peotection effect of Salmonella Pullorum at an early stage,therefore,the purpose of this study is to explore chicks immunized with Salmonella Enteritidis live vaccine at 1-day old whether it could resist the early infection of highly pathogenic Salmonella Pullorum.Before evaluating the effectiveness of the vaccine against early infection by Salmonella pullorum,this study intended to explore the interference of external environment on vaccine strains during vaccination.In this study,the Salmonella Enteritidis live vaccine was treated at 25-40 ℃,0.5-4h,then the temperature stability was evaluated by statistical vaccine survival rate,the results showed that compared to the concentration of the original solution,there was no significant difference for the concentrations of Salmonella Enteritidis live vaccine after treatment at 25 ℃-40 ℃ for 1 to 4 hours.In addition,choose several commonly used disinfectants,such as sodium hypochlorite,quinyl ammonium bromide,sodium dichloroisocyanurate,potassium monopersulfate,potassium monopersulfate,compound phenol.Minimum inhibitory concentration(MIC)and Minimum bactericidal concentration(MBC)were counted to evaluate the abilty of disinfectant tolerance.The results show that sodium hypochlorite,decyl ammonium bromide solution,potassium persulfate,sodium dichloroisocyanurate,hydrogen peroxide,and composite phenol had significant inhibitory effects on the vaccine strain at 1000mg/L,125mg/L,312.5mg/L,1875mg/L,2.35mg/L,and 820mg/L.The vaccine strain was inactivated at 12500 mg/L,125 mg/L,625 mg/L,15000 mg/L,4.68 mg/L,and 3280 mg/L.In order to evaluate the efficacy of Salmonella Enteritidis live vaccine against early Salmonella Pullorum infection,this study selected Salmonella Pullorum 20JS04 as an infectious strain,the previous research results of this strain showed that it caused more negative effects on chicenks than pullorum type.120 SPF chicks were divided into 4 groups according to their weight,30 per group.Including blank control group(CON),vaccine immune+Salmonella pullorum infection group(Avi Pro+SP),Salmonella pullorum infection group(SP),and vaccine immune control group(Avi Pro).At the age of 1 day,Vio Pro group and Vio Pro+SP group were administered Salmonella Enteritidis live vaccine 1~5 × 108CFU/feather by gavage,the CON and SP group were treated with sterile deionized water in the same manner.After 7 days,SP group and Vio Pro+SP group were orally administered Salmonella pullorum 5.5×108CFU/feather,the CON and Avi Pro group were treated with sterile PBS in the same manner.Record the weight of chickens in each group before infection and 1 week after infection,and count the mortality of chickens after infection.360 cloacal swabs and 72 environmental samples were collected for the isolation and identification.358 cloacal swabs were collect for isolation and identification of Salmonella pullorum.At the same time,120 serum samples were collected three times before infection and after 3 and 7 days of infection,detection of antibody changes in chicken serum using slide agglutination method.After 7 days of infection,randomly execute 6 chickens in each group,and their livers,spleens,hearts and bursa of Fabricius were taken for organ index determination,organ bacterial load determination and organ histopathological observation.Death results displayed,One chicken died in the Salmonella Pullorum infection group in three days after infection,and Salmonella Pullorum was found in its liver,heart,and spleen of dead chicken,while no deaths in other groups.The results of chicken dissection showed that visual pathological changes of heart swollen in the Salmonella Pullorum infection group.The pathological tissue section results showed thatAviPro+SP group showed a small amount of lymphocyte infiltration in the liver and heart,SP group showed more liver necrosis and a small amount of lymphocyte infiltration in the liver,and collagen fibers are mildly proliferated,accompanied by a little lymphocytes infiltration in the heart.Among cloacal swabs,the vaccine strain has the highest recovery rate within a week,with a detection rate of 52/60,subsequently,the overall trend showed a downward trend.Among environmental samples,the vaccine strain has the highest detection rate after 2 days of immunization,with a detection rate of 8/12,all strains were re-isolated in water tanks and feed tanks.After artificial infection,no Salmonella Pullorum was re-isolated from 358 cloacal swabs,and 120 serum samples were negative.Weight statistics display,the difference in relative daily weight gain between groups was not significant(P>0.05).The results of organ index showed that compared with the CON group,the heart index of the Avi Pro+SP group increased by 11.25%,with a significant difference(P<0.05).The heart index of the SP group increased by 16.57%,with a significant difference(P<0.01).The heart index of the SP group increased by 4.7%,with a significant difference(P<0.05)compared to the Avi Pro+SP group;The statistical results of the colonization of Salmonella pullorum in various organs showed that compared with the SP group,the colonization of the liver,spleen,and heart in the Avi Pro+SP group decreased by 5.8%,0.56%,and 4.5%,respectively,with no significant difference(P>0.05).The above results indicated that the Salmonella Enteritidis live vaccine had good temperature stability.Hydrogen peroxide,decamethylammonium bromide solution,and composite phenol disinfectant had significant inhibitory and bactericidal effects on the growth of vaccine strains.This study confirmed that immunization once of 1-day-old chickens with Salmonella Enteritidis live vaccine had a certain cross protective effect on early infection with highly pathogenic Salmonella Pullorum. |
