In order to investigate the role of sRNA OxyS in the pathogenicity of Salmonella typhi-murium infection,the OxyS gene deletion strain ATCC25241 △OxyS and the back-complemented strain ATCC25241 △OxyS/OxyS of Salmonella typhimurium ATCC25241 were constructed by using λRed homologous recombination technique.We investigated the effect of OxyS deletion on the biological characteristics and pathogenicity of Salmonella typhimurium ATCC25241.The re-sults showed that the deletion of OxyS did not affect the growth rate,the ability of biofilm forma-tion,and the ability of adhesion,invasion and intracellular survival of Salmonella typhimurium,but significantly reduced the motility of Salmonella typhimurium as well as its ability to survive in alkaline and oxidative environments.The results of mouse infection test showed that OxyS dele-tion caused a significant decrease in the virulence of Salmonella typhimurium in mice,and toxicity is reduced obviously.The qPCR results also showed that OxyS deletion could lead to changes in the transcript levels of a number of virulence-related genes of Salmonella typhimurium such as pipB,orf245,csgA,invH,tatA,sipA,sipB,and so on.The above results indicate that OxyS gene affects the biological characteristics and pathogenicity of Salmonella typhimurium and is an important virulence regulator of Salmonella typhimurium.

In order to establish a serological method for the detection of bovine respiratory syncytial virus,the prokaryotic expression of four proteins of BRSV,G,F,P,and M was carried out,and the most suitable coating antigen was screened to establish an indirect ELISA detection method.The results showed that the four recombinant proteins of BRSV,rG,rF,rP and rM were successfully expressed.The results of checkerboard screening showed that the P/N value of rG protein was the largest,which was determined to be the best coating antigen established by indirect ELISA meth-od.The optimal reaction conditions for indirect ELISA were as follows:the mass concentration of rG protein coating was 1 mg/L,37℃ for 2 h;3％BSA 37℃ block for 1 h;Serum was diluted 1∶50 and incubated at 37℃ for 1h;Secondary antibody 1∶5 000 dilution,37℃ for 30min;The color development conditions of the substrate were 37℃ for 15 min;Thirty negative sera were selected,and the cut-off value was determined to be 0.63 by the established indirect ELISA method.The re-sults of the specificity test showed that the indirect ELISA method established in this test only recognized BRSV-positive serum,and did not react with IBRV,BCoV,and BPIV3-positive serum.The results of repeatability test showed that the method had good repeatability,and the coefficient of variation within and between batches was less than 10％.The results of the sensitivity test showed that the BRSV-positive serum was still positive when diluted to 1∶8 192.The indirect ELISA method established in this experiment was used to detect 100 clinical serum samples at the same time,and the total coincidence rate of the two reached 90.48％,the positive coincidence rate was 93.42％,and the negative coincidence rate was 82.75％.The indirect ELISA established in this test can be used for the detection of bovine respiratory syncytial virus in clinical practice.

In order to establish a serological method for the detection of bovine respiratory syncytial virus,the prokaryotic expression of four proteins of BRSV,G,F,P,and M was carried out,and the most suitable coating antigen was screened to establish an indirect ELISA detection method.The results showed that the four recombinant proteins of BRSV,rG,rF,rP and rM were successfully expressed.The results of checkerboard screening showed that the P/N value of rG protein was the largest,which was determined to be the best coating antigen established by indirect ELISA meth-od.The optimal reaction conditions for indirect ELISA were as follows:the mass concentration of rG protein coating was 1 mg/L,37℃ for 2 h;3％BSA 37℃ block for 1 h;Serum was diluted 1∶50 and incubated at 37℃ for 1h;Secondary antibody 1∶5 000 dilution,37℃ for 30min;The color development conditions of the substrate were 37℃ for 15 min;Thirty negative sera were selected,and the cut-off value was determined to be 0.63 by the established indirect ELISA method.The re-sults of the specificity test showed that the indirect ELISA method established in this test only recognized BRSV-positive serum,and did not react with IBRV,BCoV,and BPIV3-positive serum.The results of repeatability test showed that the method had good repeatability,and the coefficient of variation within and between batches was less than 10％.The results of the sensitivity test showed that the BRSV-positive serum was still positive when diluted to 1∶8 192.The indirect ELISA method established in this experiment was used to detect 100 clinical serum samples at the same time,and the total coincidence rate of the two reached 90.48％,the positive coincidence rate was 93.42％,and the negative coincidence rate was 82.75％.The indirect ELISA established in this test can be used for the detection of bovine respiratory syncytial virus in clinical practice.

In order to establish a serological method for the detection of bovine parainfluenza virus type 3(BPIV3),the prokaryotic expression and purification of BPIV3 HN,NP,F,and P proteins were carried out,and the optimal protein-coated antigen was screened,and an indirect ELISA de-tection method was established.The results showed that the four recombinant proteins of BPIV3,rHN,rNP,rF,and rP were expressed,and the checkerboard titration results showed that rHN pro-tein had the highest P/N value as the coating protein,so it was used for the subsequent method es-tablishment.The optimal reaction conditions for indirect ELISA were found to be:the mass con-centration of the antigen coating was 0.5 mg/L,37 ℃ 1.5 h,5％skim milk,overnight blocking at 4 ℃,serum dilution at 1∶50,incubation at 37 ℃ 1 h,secondary antibody dilution at 1∶10 000 and incubation at 37℃ 0.5 h,substrate reaction conditions were 37℃ for 12 min.The results of speci-ficity experiments showed that the established method could specifically identify BPIV3 antibody-positive serum with a sensitivity of 1∶800,and the coefficient of variation in the detection of intra-and inter-assay repeatability was less than 10％,and the overall coincidence rate of the same batch of samples detected with the SVANOVIR kit was 92.22％.This method was used to detect 192 se-rum samples in Hebei Province,and the positive rate of BPIV3 antibody in serum was 66.15％.The indirect ELISA detection method of BP1V3 antibody constructed in this study is suitable for large-scale clinical serological investigations,and provides valuable data support for the research and de-velopment of BPIV3 antigen and antibody detection kits in China.

In order to establish a serological method for the detection of bovine parainfluenza virus type 3(BPIV3),the prokaryotic expression and purification of BPIV3 HN,NP,F,and P proteins were carried out,and the optimal protein-coated antigen was screened,and an indirect ELISA de-tection method was established.The results showed that the four recombinant proteins of BPIV3,rHN,rNP,rF,and rP were expressed,and the checkerboard titration results showed that rHN pro-tein had the highest P/N value as the coating protein,so it was used for the subsequent method es-tablishment.The optimal reaction conditions for indirect ELISA were found to be:the mass con-centration of the antigen coating was 0.5 mg/L,37 ℃ 1.5 h,5％skim milk,overnight blocking at 4 ℃,serum dilution at 1∶50,incubation at 37 ℃ 1 h,secondary antibody dilution at 1∶10 000 and incubation at 37℃ 0.5 h,substrate reaction conditions were 37℃ for 12 min.The results of speci-ficity experiments showed that the established method could specifically identify BPIV3 antibody-positive serum with a sensitivity of 1∶800,and the coefficient of variation in the detection of intra-and inter-assay repeatability was less than 10％,and the overall coincidence rate of the same batch of samples detected with the SVANOVIR kit was 92.22％.This method was used to detect 192 se-rum samples in Hebei Province,and the positive rate of BPIV3 antibody in serum was 66.15％.The indirect ELISA detection method of BP1V3 antibody constructed in this study is suitable for large-scale clinical serological investigations,and provides valuable data support for the research and de-velopment of BPIV3 antigen and antibody detection kits in China.

In order to investigate the role of sRNA OxyS in the pathogenicity of Salmonella typhi-murium infection,the OxyS gene deletion strain ATCC25241 △OxyS and the back-complemented strain ATCC25241 △OxyS/OxyS of Salmonella typhimurium ATCC25241 were constructed by using λRed homologous recombination technique.We investigated the effect of OxyS deletion on the biological characteristics and pathogenicity of Salmonella typhimurium ATCC25241.The re-sults showed that the deletion of OxyS did not affect the growth rate,the ability of biofilm forma-tion,and the ability of adhesion,invasion and intracellular survival of Salmonella typhimurium,but significantly reduced the motility of Salmonella typhimurium as well as its ability to survive in alkaline and oxidative environments.The results of mouse infection test showed that OxyS dele-tion caused a significant decrease in the virulence of Salmonella typhimurium in mice,and toxicity is reduced obviously.The qPCR results also showed that OxyS deletion could lead to changes in the transcript levels of a number of virulence-related genes of Salmonella typhimurium such as pipB,orf245,csgA,invH,tatA,sipA,sipB,and so on.The above results indicate that OxyS gene affects the biological characteristics and pathogenicity of Salmonella typhimurium and is an important virulence regulator of Salmonella typhimurium.

Background With the rapid industrialization, cadmium has become a primary heavy metal pollutant in cultivated land soil in China, which seriously affects human health. Previous studies have found that cadmium exposure associates with cognitive dysfunction in individuals, but there is a lack of research on the mechanism of cadmium exposure associated cognitive impairment in offspring in early life which is more vulnerable to various toxins and crucial for development of the neuro. Objective To explore the potential mechanism of brain-derived neurotrophic factor/tyrosine kinase receptor B (BDNF-TrkB) signaling pathway in cognitive dysfunction in mice after cadmium exposure in early-life. Methods Twelve 8-week-old C57BL/6 pregnant mice were randomly divided into 2 groups, namely control group and cadmium exposure group, with 6 mice in each group. The exposure period was from pregnancy day 4.5 to lactation day 21 (E4.5-P21), during which distilled water or cadmium chloride solution (2.5 mg·kg⁻¹·d⁻¹) was given. After lactation, the offspring of the control group and the cadmium exposure group were given distilled water until 8 weeks of age. Then the toxicity effects of cadmium exposure on mice were evaluated by body weight and selected biochemical indicators. The cadmium content in brain was detected and the learning and memory ability was tested by Y maze and Morris water maze to evaluate cognitive function of offspring mice. Histopathological changes of the hippocampus were observed after Nissl staining and Golgi staining. The mRNA and protein expression levels of the BDNF-TrkB pathway and synapse were detected by real-time quantitative PCR (qPCR) and Western blot. Results Compared with the control group, no significant change was found in body weight, liver or kidney function in the cadmium exposure group (P> 0.05). However, compared with the control group, the cadmium content in brain was increased in the cadmium exposure group (P<0.001). The behavioral changes associated with cognitive dysfunction were positive in the cadmium exposure group (all P<0.05). The histopathological observation after Nissl staining showed abnormal tissue structure, decreased number of neurons and increased karyopyknosis in the cadmium exposure group (P<0.01).The spine density of Golgi staining was decreased in the cadmium exposure group (P<0.001). The BDNF-TrkB pathway-related mRNA and the synapse-related mRNA in the hippocampus were reduced in the cadmium exposure group (all P<0.05). The expression levels of BDNF-TrkB pathway-related proteins and synapse-related proteins in the hippocampus were also reduced in the cadmium exposure group (P<0.05). Conclusion Early-life cadmium exposure may induce synaptic dysplasia and lead to cognitive dysfunction by down-regulating the BDNF-TrkB signaling pathway in mice.

Bovine leukemia virus(BLV)mainly causes bovine B-cell malignant lymphoma,which causes immunosuppression and leads animals susceptible to other diseases.BLV has been detected all over the world except in Western Europe.Antibodies to BLV have been detected in humans,and reverse transcribed DNA of BLV were detected in breast tissue sections and lung tumors,which in-dicate that BLV is a potential zoonotic disease.At present,there are no effective treatment methods or commercial vaccines for BLV.An in-depth understanding of the development of BLV detection technology will help researchers choose suitable detection methods,avoid invalid detection results,and meet the requirements of disease prevention and control.In view of this,this paper reviews 19 detection technologies of BLV including cytology detection,nucleic acid detection,and serology de-tection.The advantages,disadvantages,and scope of application were also analyzed,which provide theoretical guidance for the prevention and control of bovine leukemia.

The eutR gene deletion mutant of Salmonella enteritidis was successfully constructed by homologous recombination.Through the study of its biochemical characteristics,motility,resist-ance to stress in vitro and survival ability in RAW 264.7 cells,it was found that the biochemical characteristics and motility of the eutR gene deletion mutant of Salmonella enteritidis had no sig-nificant change compared with the wild type of Salmonella enteritidis.The ability of eutR gene de-letion strain of Salmonella enteritidis to resist acid,alkali and oxidation was significantly reduced,while the ability to resist heat was not significantly changed;the survival ability of eutR gene dele-tion strain in RAW 264.7 cells was significantly reduced compared with the wild type.In order to further analyze the effect of eutR gene on the expression of virulence factors of Salmonella enterit-idis,the relative expression levels of invH,ssav,ssrA,xthA,orf245,sodC,lrp,mrr1 and hflk virulence genes of the deletion strain and the wild strain were detected by SYBR Green PCR.It was found that the expression of the virulence factors mentioned above in the eutR gene deletion strain of Salmonella enteritidis was significantly down-regulated compared with that in the wild-type strain.The LD50 of the eutR gene-deleted strain of Salmonella enteritidis was determined by ani-mal experiments,and the results showed that the LD50 of the eutR gene-deleted strain was higher than that of the wild-type strain,indicating that the eutR gene could affect the virulence of Salmonella.This study clarified the effect of eutR gene on the survival ability,some biological characteristics and virulence of Salmonella enteritidis in macrophages,and provided a new gene knockout target for the development of attenuated Salmonella enteritidis genetic engineering vac-cine.

Chicken coccidia specialize in growing and reproducing within the epithelial cells of the chicken intestinal mucosa,posing a threat to the health of the chicken flock.However,traditional chemical drugs are difficult to pass through the cell barrier and can easily lead to the emergence of drug-resistant strains and residual veterinary drugs,posing a huge challenge to the prevention and control of coccidiosis.Therefore,it is necessary to develop new strategies against coccidiosis.Nano-drugs have the advantages of good biocompatibility,easy modification,and high efficiency,impro-ving the penetration of cell membranes while reducing drug toxicity and side effects.They are ex-pected to be applied in the prevention and treatment of coccidiosis.This article introduces various nanomedicines for treating chicken coccidiosis,summarizes their advantages compared to tradition-al formulations,focuses on the application of nanomedicines in the treatment of chicken coccidio-sis,elucidates the existing problems of nanomedicine treatment for chicken coccidiosis,and looks forward to the challenges and future development directions in this field,in order to provide impor-tant references for the development of nanomedicines for treating chicken coccidiosis.