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.

Effects of Vaccination with the C-Strain Vaccine on Immune Cells and Cytokines of Pigs Against Classical Swine Fever Virus.

The attenuated C-strain vaccine against classical swine fever virus (CSFV) is one of the safest and most effective attenuated vaccines. However, little is known of the host immune response after vaccination with the C-strain vaccine. Blood samples from vaccinated pigs were collected to evaluate the number of immune cells, the level of specific CSFV antibody, and related cytokines induced by the vaccination of C-strain vaccine. The C-strain nucleic acid was gradually removed and specific antibody to vaccine kept increasing; the amount of the lymphocyte, Tc cell, and Th cell increased; some inflammatory cytokines such as interleukin (IL)-1 and tumor necrosis factor-α mainly showed downregulated trends, but IL-6 and IL-8 were upregulated greatly; IL-2, IL-4, IL-5, IL-12p40, IL-13, interferon (IFN)-I, and Toll-like receptors (TLRs) kept high expression level after 28 days postvaccination (dpv); IFN-γ was upregulated slightly at 5 and 9 dpv, respectively. These results suggest that the C-strain vaccine induces a Th2 cell response to produce the specific antibody. The vaccine virus replicates at very low level. C-strain vaccine burden has close relationship with the expression of TLRs. The overexpression of TLRs initiates the innate immune system to clear up the vaccine. Meanwhile, ILs expressed by immune system induce the differentiation of B cells and produce specific antibody.

Dynamic distribution and tissue tropism of classical swine fever virus in experimentally infected pigs.

BACKGROUND: Classical swine fever (CSF), caused by the Classical swine fever virus (CSFV), is an Office International des Epizooties (OIE) notifiable disease. However, we are far from fully understand the distribution, tissue tropism, pathogenesis, replication and excretion of CSFV in pigs. In this report, we investigated the dynamic distribution and tissue tropism of the virus in internal organs of the experimentally infected pigs using real-time RT-PCR and immunohistochemistry (IHC). RESULTS: A relative quantification real-time PCR was established and used to detect the virus load in internal organs of the experimentally infected pigs. The study revealed that the virus was detected in all 21 of the internal organs and blood collected from pigs at day 1 to day 8 post infections, and had an increasing virus load from day 1 to day 8 post infections. However, there was irregular distribution virus load in most internal organs over the first 2 days post infection. Blood, lymphoid tissue, pancreas and ileum usually contain the highest viral loads, while heart, duodenum and brain show relatively low viral loads. CONCLUSIONS: All the data suggest that CSFV had an increasing virus load from day 1 to day 8 post infections in experimentally infected pigs detected by real-time RT-PCR, which was in consistent with the result of the IHC staining. The data also show that CSFV was likely to reproduce in blood, lymphoid tissue, pancreas and the ileum, while unlikely to replicate in the heart, duodenum and brain. The results provide a foundation for further clarification of the pathogenic mechanism of CSFV in internal organs, and indicate that blood, lymphoid tissue, pancreas and ileum may be preferred sites of acute infection.

A novel RT-LAMP assay for rapid and simple detection of classical swine fever virus.

A simple and rapid assay for the detection of Classical swine fever virus (CSFV) was established using reverse transcription loop-mediated isothermal amplification (RT-LAMP). This study describes the amplification of the genomic RNA of CSFV under isothermal conditions (63 °C) within one hour, using a set of six primers (two outer primers, two inner primers and two loop primers). This RT-LAMP assay showed 100-fold higher sensitivity than the standard RT-PCR method and identified eighteen additional positive cases that were negative when tested by RT-PCR. This RT-LAMP was able to detect all the 13 strains of CSFV but not the BVDV. PRRSV. SIV. PRV-PCV, thus showed a good specificity. Products amplified by RT-LAMP can be visualized by agarose gel electrophoresis and in addition, either as a white precipitate at the bottom of the tube after a pulse spin or as a color change when dyed with SYBR Green I which are visible to the naked eye. Because RT-LAMP is low-cost and produces rapid results, it has the potential to be an excellent tool for CSFV surveillance in the field, especially in developing countries.

[The changes of peripheral blood leucocytes subpopulation after challenge with CSFV virulent strain Shimen].

To investigate the effects of classical swine fever virus (CSFV) virulent strain Shimen (SM) infection on piglets peripheral blood leucocytes, the 60-days weanling piglets were infected with the shinen strain and the peripheral blood samples of the piglets were collected to analyze the kinetics of the CSEV nucleic acid, the peripheral blood leucocytes subpopulation and SLA molecule expression on the peripheral blood leukocytes. The results showed that the piglets rectal temperature increased 48 hours after intramuscular injection of CSFV SM strain, the CSFV nucleic acid was detected in the peripheral blood at 2DPI, the content of CSFV nucleic acid increased and up-regulated to a peak at 6DPI as 10 (4.84 +/- 0.98 times as 2DPI. The amount of WBC, LYM and PLT significantly decreased, where in the amount of WBC decreased to 65.87% at 1DPI and 50% at 2DPI respectively; the amount of LYM decreased to 70.68%, 47.88% and 23.29% at 1DPI, 2DPI, and 3DPI, respectively; the amount of PLT decreased day by day and to 34.59% at 6DPI; the amount of NK, gammadeltaT, Tc, Th, CD3+ CD4+ CD8+ and CD3- CD4- CD8- cells decreased after infection; 78.49% of NK cells decreased at 1DPI and then there was no significant change from 2DPI to 6DPI. The amount of gammadeltaT, Tc, CD4- CD8- CD3-,CD4+ CD8+ CD3+ cells decreased to 41.74%, 43.83%, 15.87%, and 32.96% at 3DPI, respectively, However, the amount of T helper cells decreased continually to 42.95% at 6DPI; the amount of SLA I positive lymphocytes decreased significantly and the amount of SLA I positive CD3 cells decreased to 23.07% and 15.38% at 1DPI and 2DPI respectively; the SLA I positive granulocytes increased continually from 92.20% at 1DPI to 98.30% at 3DPI; the amount of CD3 SLA II + cells in lymphocytes decreased from 1.38% at 1DPI to 0.22% at 2DPI, while the SLA II + granulocytes increased continually to a peak at 3DPI and 53.76% of granulocytes expressed the SLA II molecule, but the percentage of the granulocytes expressing SLA II molecules decreased to 12.54% and 4.06% at 4DPI and 5DPI respectively. The study indicated that the CSFV SM strain infection could escape the immune surveillance and cause immunosuppression through inhibiting the host's innate antiviral immunity and the SLA molecule expression to affect the antigen presentation.

[Distributions of pathogenic capsular types and in vitro antimicrobial susceptibility of different serotypes of Streptococcus suis isolated from clinically healthy sows from 10 provinces in China].

OBJECTIVE: To determine the distributions of major pathogenic capsular types and in vitro antimicrobial susceptibility of different serotypes of Streptococcus suis isolated from clinically healthy sows in China. METHODS: Tonsil specimens of clinically healthy sows from 10 different provinces in China were collected, a total of 421 S. suis were isolated. Capsular types of S. suis were decided using the sera agglutination reaction. Antimicrobial susceptibility testing was performed using a broth microdilution method and the differences between serotypes were decided statistically. RESULTS: The prevalent capsular types of S. suis isolated from clinically healthy sows were 9 (26.6%), 3 (23.5%) and 7 (15.7%) types, respectively. 7.4% of isolates were confirmed to be S. suis type 2. Overall, differences in antimicrobial susceptibility among serotypes of S. suis were found. By comparison, lower resistance was observed for S. suis type 2 from clinically healthy sows. CONCLUSION: The prevalence of pathogenic S. suis serotypes from clinically healthy sows again indicates S. suis is a conditional pathogenic bacterium. Differential prevention and treatment regimes should be considered according to antimicrobial susceptibility of different serotypes of S. suis.