Background: Brucellosis is a widespread disease that affects animals and humans. The live attenuated Brucella abortus A19 strain is used for vaccination against brucellosis in China. In addition, the main mechanisms supporting the residual toxicity of A19 have not been elucidated. Here, we performed a comprehensive comparative analysis of the genome-wide sequence of A19 against the whole genome sequences of the published virulent reference strain 9-941. The primary objective of this study was to identify candidate virulence genes by systematically comparing the genomic sequences between the two genomes. Results: This analysis revealed two deletion regions in the A19 genome, in which all included large fragments of 63 bp, and one of their gene function is related to ABC transporter permease protein. In addition, we have identified minor mutations in important virulence-related genes that can be used to determine the underlying mechanisms of virulence attenuation. The function of its virulence gene covers LysR family transcriptional regulator, outer membrane, MFS transporter and oxidoreductase etc. At the same time, a PCR differential diagnosis method was constructed, which can distinguish A19, S19 and most other commonly used Brucella viruent strains and vaccine strains. Conclusion: The data may help to provide resources for further detailed analysis of mechanisms for other Brucella vaccines. It laid the foundation for further distinguishing between vaccine immunity and virulent strains infection.

Background: The hindgut epithelial barrier plays an important role in maintaining absorption and immune homeosrasis in ruminants. However, there is little information available on changes of colon epithelial barrier structure and function following grain-induced subacute ruminal acidosis (SARA). The objective of this study was to investigate the effects of SARA on colon epithelial morphological structure, permeability and gene expression involved in epithelial barrier function using dairy goats as a ruminant model. Methods: Twelve mid-lactating Sannan dairy goats (62.13 ± 4.76 kg) were randomly divided into either control (n = 6) or SARA treatment (n = 6). Control goats were fed a mixed diet (non-fiber carbohydrates/neutral detergent fiber (NFC/NDF) =1.15) for 60 days, SARA induction goats were given 4 mixed diets with NFC to NDF ratios of 1.15, 1.49, 2.12 and 2.66 to induce development of SARA. The duration of each diet was 15 d including 12 d for adaption and 3 d for sampling. Continuous ruminal pH recordings were utilized to diagnose the severity of SARA. Additionally, Plasma and colonic tissue were collected to evaluate the epithelial tissue morphological structure, permeability and expression of tight junction (TJ) protein using histological techniques, Ussing chamber, real-time PCR and western blotting. Results: Profound disruption in the colonic epithelium was mainly manifested as the electron density of TJ decreased, intercellular space widened and mitochondria swelled in SARA dairy goats. Epithelial Isc, Gt and the mucosal-to-serosal flux of FD4 ( P < 0.05) were increased, PD was decreased in SARA dairy goats compared with the control. SARA increased the plasma LPS ( P < 0.001), D-lactic acid contents ( P = 0.025) and DAO activity ( P = 0.003). Increased gene and protein expression of claudin-1 and occludin ( P < 0.05) were observed in colonic epithelium of SARA goats. Conclusion: Overall, the data of present study demonstrate that SARA can impair the barrier function of the colonic epithelium in dairy goats, which is associated with severe epithelial structural damage and increased permeability and changes in the expression of TJ proteins.