Whole-genome sequencing of rough <i>Brucella melitensis</i> in China provides insights into its genetic features

<i>Brucella</i> spp. can cause the zoonosis brucellosis, which affects public health and safety and even economic development. <i>B. melitensis</i> has a smooth phenotype, while 28 <i>B. melitensis</i> isolates had a rough phenotype in 2018. In this study, rough phenotype detection and whole genome sequencing methods were used to analyze the genetic features of rough <i>B. melitensis</i>. A drug susceptibility test was also performed. The results showed that the rough <i>B. melitensis</i> strains originated from strains isolated in China rather than from foreign strains. Furthermore, an MS tree showed that 9 complexes to be epidemic in China. For the rough <i>B. melitensis</i> strains, expression of the metabolic function genes varied in the earlier stages of evolution compared to the cellular process and signalling function genes. Expression of some transcriptional regulatory factors also varied in the later stages of evolution, and compared to MFS transporter genes, ABC transporter genes varied in the earlier stages. Moreover, as there was no significant difference in rifampicin, doxycycline and streptomycin susceptibility between the smooth and rough <i>B. melitensis</i> strains, treatment of brucellosis was not affected by strain type. This study provided important information for understanding the genetics and evolution of rough <i>B. melitensis</i> in China.

布鲁氏菌属（Brucella）可引发人畜共患病布鲁氏菌病，该疾病不仅威胁公共卫生安全，更会对经济发展造成不利影响。羊种布鲁氏菌（B. melitensis）通常表现为光滑表型，但2018年的研究中发现28株羊种布鲁氏菌分离株呈现粗糙表型。本研究采用粗糙表型检测与全基因组测序技术，分析了粗糙表型羊种布鲁氏菌的遗传特征，并开展了药物敏感性试验。结果表明，本次研究中的粗糙表型羊种布鲁氏菌菌株均分离自国内菌株，而非境外来源菌株。MS系统发育树（MS tree）分析显示，国内存在9个流行序列复合体。相较于细胞过程与信号功能基因，粗糙表型羊种布鲁氏菌的代谢功能基因在进化早期的表达模式存在显著差异；部分转录调控因子的表达模式在进化后期出现分化，且ATP结合盒转运蛋白（ABC transporter）基因的表达变化早于主要易化因子超家族转运蛋白（MFS transporter）基因。此外，光滑表型与粗糙表型羊种布鲁氏菌菌株对利福平、多西环素及链霉素的敏感性无显著差异，提示菌株表型不会影响布鲁氏菌病的临床治疗。本研究为解析国内粗糙表型羊种布鲁氏菌的遗传特性与进化机制提供了重要参考依据。