Bacteriological and molecular typing of Clostridium perfringens strains isolated in retail beef in Beijing, China.

Clostridium perfringens is an important zoonotic pathogen. This study was designed to explore the prevalence and toxin types of C. perfringens in retail beef collected from Beijing, China. Among 221 beef samples collected, 53 samples were positive for C. perfringens, resulting in the average prevalence as 23.98%. By toxin gene-based typing, the most C. perfringens strains belong to type A (96.23%, 51/53), only 2 strains were identified as type D. By a multi-locus sequence typing (MLST)-based analysis, a total of 36 sequence types (STs) were detected, and the most STs (n=30) represented just a single strain. These finding suggested that the prevalence of C. perfringens in retail beef in Beijing was considerably high and these bacteria displayed extreme diversity in genetics.

Brucellosis in China: history, progress and challenge.

Brucellosis is a neglected zoonosis. It causes acute febrile illness and a potentially debilitating chronic infection in humans, and livestock infection has substantial socioeconomic impact. Over the past two decades, improvements have been made to better understand the various aspects of human and animal brucellosis. Meanwhile, especially in the developing world, immense challenges that remain in controlling and eradicating brucellosis are novel diagnostics tools and efficacious vaccines. Here, we will focus on the remarkable issues on epidemiological survey, as well as the priority and challenge of brucellosis in China. Brucellosis will be controlled with meaningful collaboration between local and public partnerships effectively applying a One Health framework.

[Construction and characterization of a brucella suis S2 strain with a chloramphenicol resistance marker].

Vaccination has not been used widely because of the interference in the discrimination between infected and vaccinated animals in immune-screening procedures. In the present study, chloramphenicol resistance gene (Cm(r)) was cloned into the genomic DNA of brucella suis S2 strain by homologous recombination with knocking out the WbkC gene, and obtained the recombinant rS2-WbkC. Further study confirmed that rS2-WbkC was conversed into rough-phenotype form smooth-phenotype. The recombinant keeps the ability to chloramphenicol resistance after 25 passages in tryptic soy agar (TSA). Mice tests showed rS2-WbkC offered similar protection to S2 strain, but more safe than S2. Serum collected form rS2-WbkC immunized mice could be easily distinguished from antiserum produced by smooth-phenotype brucella abortus. In view of these result, rS2-WbkC is a promising candidate for vaccine strain.

[The application and research advances of Brucella vaccines].

Brucellosis is a crucial zoonosis caused by Brucella, which has some traits of wide hosts, great infectivity and difficulty in cure. Brucellosis caused great losses to farming and people's health. Vaccination is the main measure used to control Brucellosis, and some attenuated Brucella strains were often used as vaccines. To find more effective vaccines, Scientists are now constructing recombinant strains, DNA vaccines and subunit vaccines, as well as inducing new attenuated strains from isolations. The present applications of B. abortus strain 19 (S19) , B. melitensis Rev. 1 (Rev. 1), B. suis strain 2 (S2), B. abortus strain 45/20 (45/20) and rough strain B. abortus 51 (RB51) were discussed. And some recent research work on Brucella vaccines, such as Brucella recombinant vaccines, DNA vaccines and so on, were reviewed in this paper.

[Study on the characterization of the bi-directional promoter between pp38 gene and 1.8kb mRNA transcripts of Marek's disease viruses].

The bi-directional promoter between pp38 gene and 1.8kb mRNA transcripts of Marek's disease viruses (MDV) was divided into two single-direction promoters from the replication of MDV genomic DNA. The pp38 gene was cloned into pUC18 vector for plasmid pUC-pp38. Then the complete bi-directional promoter was cloned into pUC-pp38 in two directions to form plasmids pPro(f)pp38 and pPro(r)pp38, and the divided two single directional promoters were cloned in pUC-pp38 for plasmids pdPro(f)pp38 and pdPro(r)pp38. 24 to 48 hours after transfection to chicken embryo fibroblast (CEF) cells, the expression of pp38 could be detected in above 4 samples with Indirect Immuno-fluorescent Assay (IFA). In order to analysis the activity of the promoter quantificationally, CAT was used as the report gene. The complete or divided promoters were cloned into pCAT-Basic vector for plasmids pPro(f)CAT, pPro(r)CAT, pdPro(f)CAT and pdPro(r)CAT. The activity of CAT was measured from the lysed CEF cells, when they were transfected for 48 hours by the above four plasmids, respectively. The results showed the activity of the divided promoters reduce on both directions, especially for the direction of 1.8kb mRNA transcript, nearly down to 1/41.

[PCR detection of PCV-2 and PRRSV in porcine pleuropneumonia samples].

PCV-2 (Porcine circovirus type-2, PCV-2) and PRRSV (Porcine reproductive and respiratory syndrome virus, PRRSV) were detected by PCR from 253 porcine pleuropneumonia samples and 125 clinically healthy lung samples were collected from different districts of Shandong province. The results showed that 171 samples for PCV-2 and 101 samples for PRRSV were positive. The positive ratio were 67.5% and 40%, respectively. The co-infection number of PCV-2 and PRRSV was 68 in 253 samples, the positive ratio was 26.8%. While in the clinically healthy samples, only 21 samples for PCV-2 and 12 samples for PRRSV were detected positive, the positive ratio were 16.8% and 9.6%, respectively, no co-infection samples were found. Statistical result showed significant difference between positive ratio for PCV-2 and PRRSV in porcine pleuropneumonia samples and that of in clinically healthy samples. The above results demonstrated that there maybe some relationship between the infection of porcine pleuropneumonia and PCV-2 and PRRSV in pigs.

[Construction of infectious clone of subgroup J avian leukosis virus strain NX0101 and its pathogenicity].

By using PCR, 3 fragments of provirus cDNA of avian leukosis virus (ALV-J) strain NXO101 were amplified from the genomic DNA of ALV-J infected cells,and then combined in the right direction and sequences into recombinant plasmid pALV-J-NX, containing the whole genome of NX0101. After transfection of chicken embryo fibroblast (CEF) cells with plasmid pALV-J-NX DNA, the rescued virus was identified in CEF by indirect fluorescence antibody test with ALV-J specific monoclonal antibody JE9. The rescued virus could replicate in CEF at a titer of 10(5.6)/mL. The chicken experiment demonstrated that the rescued virus was still able to induce tumors in commercial meat-type broilers.