Prokaryotic Expression of Gene Encoding Glutamate Dehydrogenase of Streptococcus suis Serotype 2 and Preparation of Polyclonal Antibodies against Its Expressed Products

[ Objective] To obtain detection antigen for diagnosis of Streptococcus suis infection. [ Method] The complete ORF of glutamate dehy- drogenase （GDH） gene was amplified from the genomic DNA of Streptococcus suis serotype 2 strain SC22 isolated in Sichuan Province by poly- merase chain reaction （PCR）. The resulting product was cloned into the prokaryotic expression vector pET-30a, which was then transformed into E. coil BL21 （DE3）. The identified positive transformants were screened for expression induced by IPTG. The expression products were subjected to SDS-PAGE and the recombinant protein was purified by nickel ion-agarose affinity chromatography. New Zealand rabbits were immunized with the purified recombinant GDH protein to prepare polyclonal antibodies. Titers of the anti-serum were determined by indirect ELISA and Western blot assay. [ Result] The recombinant GDH protein was effectively expressed in the host bacteria, and highly pure recombinant protein was obtained by nickel ion-agarose affinity chromatography. High-titer anti-serum against the recombinant protein was obtained. As evidenced by western blot as- say, the sera could react specifically with the lysates of all detected Streptococcus suis strains. In addition, the recombinant GDH protein could re- act specifically with serum samples collected from five pigs experimentally infected by strain SC22. [ Conclusion] The expressed GDH fusion protein has some common epitopes of natural GDH and can be used as detection antigen to develop ELISA and other diagnostic methods.

Isolation and Identification of Serotype O101 Bovine Pathogenic Escherichia coli with Multidrug Resistance

[Objective]The paper was to isolate and identify a multidrug-resistance bovine pathogenic Escherichia coli. [Method]The dead cases of calf diarrhea were collected from a large-scale beef cattle farm,and the isolated pathogen was conducted molecular identification,serological identification,drug sensitivity test,and mice pathogenicity test,respectively. Targeted therapy was undertaken thereafter to herds. [Result] One strain of bovine pathogenic E. coli,serotype O101 with strong multidrug resistance and high pathogenicity to mice,was successfully isolated. It was used to develop sensitive drug for timely treating follow-up diarrhea calves,and successfully controlled calf diarrhea in the farm. [Conclusion]The results provide a basis for effective prevention and control of bovine colibacillosis.

Detection of Patulin in Dairy Products by ELISA

The content of patulin in dairy products was detected by rapid ELISA assay. The pretreatment of samples was simple, with wide range of application. The standard product showed good linear relationship with the range of 0-5.4 μg/kg, and the linear relationship reached 0.999 3, with high sensitivity. It took shorter time, with a total time-consumption of 1 h. Moreover, it had good repeatability for analytical requirements.

Prokaryotic Expression and Immunogenicity of Dominant Epitope Region of Goose Parvovirus Structural Protein VP3

[Objective] The paper was to develop a subunit vaccine candidate for prevention and control of goose parvovirus infection. [Method]Based on the prokaryotic expression system, the antigenic epitopes and locations of the structural protein VP3 were predicted by software analysis,and the region displaying a large portion of antigenic epitopes was amplified by PCR. The target VP3 DNA fragment was inserted into pET-30 a-VP3 vector, was transformed into Escherichia coli BL21 competent cells for protein expression and animal test. The SPF chickens were immunized with the recombinant protein and the antisera were collected for neutralization test by using a goose embryo fibroblast. [Result] The recombinant plasmid was constructed, and the target region of VP3 protein was expressed efficiently in a soluble form. The neutralizing titers of antisera could reach up to-2.608. [Conclusion] The target region displaying a large portion of antigenic epitopes of the structural protein VP3 could be expressed efficiently in soluble form, and the expressed protein could induce neutralizing antibodies in SFP chicken.