Origin tracking of Brucella strain B. melitensis bv.3 ARQ-070 using biochemical and genomic studies.

Objective: To conduct an origin tracking and genomic study of the Brucella strain B. melitensis bv.3 ARQ-070, with the aim of addressing the challenges posed by the highly conserved genome of Brucella to conventional typing methods and to gain an understanding of the geographic distribution and interspecies transmission of this pathogen in China.

Methods: Differentiation and genotyping were established via biochemical profiles and polymerase chain reaction (AMOS-PCR). Illumina MiSeq® was applied to sequence the Brucella isolates. Using multilocus sequence typing (MLST) multilocus sequence typing and Fisher's exact test was used for the KEGG enrichment analysis of differential genes. Differential gene protein PPI network analysis was conducted using the STRING database and visualisation was performed using.

Results: According to the final identification results of an A/M serum agglutination test. ARQ-070 was identified as the No. 3 white spirulina biological variety, and mM was identified as the No. 1 white Spirulina biological variety. The genetic information of this strain is very close to that of the M5 vaccine strain, suggesting possible vaccine-escape infection. In the comparative genomics analysis with B. melitensis bv.1 16 M, the main differences between the B. melitensis strains were found to be concentrated in the genes related to amino acid metabolism and environmental perception. A base mutation was found in the Brucella gene virB9, which is associated with the key virulence factor of the type IV secretion system (T4SS), but this mutation did not lead to changes in the protein's tertiary structure, and the strain did not lose its infectivity.

Conclusion: The study discovered a base mutation in the virB9 gene of Brucella, which is linked to T4SS but does not affect the protein's structure or the strain's infectivity. This mutation could influence public health approaches to detecting and preventing Brucella transmission. Future research aims to analyse a wider range of Brucella strains for a deeper understanding of their epidemiology.