Minimum Core Genome Sequence Typing of Brucella From China

The Gram-negative bacterial genus Brucella includes six classic species based on host specificity,pathogenicity and phenotypic differences.Four more Brucella species were identified in 2007.Although many Brucella genomes have been sequenced,genome sequences and analysis of Brucella strains isolated in China are still scarce.An efficient genome-based Brucella typing method is also needed.In this study,we used the minimum core genome(MCG)typing method to identify and type Brucella strains.Twenty Brucella isolates fromChinawere newly sequenced.The genome sequences of 55 representative Brucella strainswere downloaded.Among the 75 genomes,1089 genes and 52,030 single nucleotide polymorphisms(SNPs)shared by all isolates were considered as the MCG genes and MCG SNPs.Using these 52,030 MCG SNPs,Brucella was divided into six MCG groups.In addition,average nucleotide identity(ANI)values and the distributions of 184 virulence genes were all computed.The proportions of virulence genes were 90.96%,93.56%,95.89%,86.04%,85.78%and 91.87%for MCG groups 1 to 6,respectively.The intragroup ANI values were higher than the intergroup values,further confirming the validity of the MCG taxonomy classification.Brucella melitensis and Brucella abortus,the two main Brucella species pathogenic to humans,were well separated from other species.With the development and cost reduction of next-generation sequencing,theMCG typing method can be used for rapid identification of Brucella,which can contribute to the rapid diagnosis of brucellosis and ensure timely and effective treatment.